VEGETABLE ORGANOGRAPHY AND PHYSIOLOGY.

This division includes a consideration of the minute structure of the various parts of plants, of the changes which they undergo during their growth and development, of the forms which they assume, and of the functions which they perform. It is the foundation of the science, and without a thorough knowledge of it there can be no correct ideas in regard to classification.

CHAPTER I.

ELEMENTARY TISSUES OF PLANTS.

1.—GENERAL REMARKS ON MICROSCOPIC VEGETABLE STRUCTURE.

The study of the elementary tissues of plants is included under Vegetable Histology (τοις, web or tissue). These tissues are few and simple. They consist of organs to which the names of Cells and Vessels have been given. The former are minute bladders or vesicles (Fig. 1), varying in size and form, which, when united together, constitute Cellular tissue (Fig. 2); while the latter are closed tubes of an elongated form, frequently tapering to each end (Fig. 3), and, when combined, constituting Vascular tissue. The distinction between cells and vessels is founded on their comparative length. Occasionally, however, cells become lengthened, as in the case of some hairs, and the filamentous or thread-like tissue of Fungi, so as not to differ from vessels as regards length.

Such long cells are distinguished chiefly by the thinness and delicateness of their texture.

The primary form of the elementary organs of plants is a closed spherical or elongated vesicle or utricle, having its walls composed of a membrane, and containing a fluid. If it still remain closed after its development is completed, then it receives the name of Cell; but if a row of utricles arranged in lines become united in the course of development so as to form a tube with an uninterrupted cavity by absorption of the cross walls, then a Vessel is produced.

On making a transverse section of a succulent stalk, such as that of Rhubarb, or of a Cucumber or Melon, we perceive, by the aid of a glass, circumscribed angular meshes and rounded openings; and, in a longitudinal section of the same stalk, similar meshes are also seen with long tubes of various kinds. The angular spaces, as seen in Figure 4, are sections of cells, while the rounded openings are the sections of vessels. The membrane forming the walls of both cells and vessels is composed of a substance called Cellulose, in many respects resembling starch, but differing in giving a yellow in place of a blue colour, with iodine. The membrane has in general no visible pores or perforations, but fluid matters pass through it easily. Some plants, such as Sea-weeds, Mushrooms, and Lichens, consist of cellular tissue alone, and hence are called Cellular plants; while others, such as ordinary flowering plants, consist of cells and vessels combined, and receive the name of Vascular plants. In studying the minute structure of plants, it is necessary to call in the aid of the microscope. A simple microscope is the most useful instrument for a botanical student. By means of it the object is viewed directly through a lens or set of lenses, so arranged as to be capable of being adjusted by means of a screw to the exact focal distance, and of being moved over different parts of the object. In examining structures in the fields, Gairdner's portable microscope is the best. In the study of very minute tissues, and especially in physiological researches, the achromatic compound microscope is required, by means of which the object is not viewed directly, but an image of the object is formed by one lens, or set of lenses (the objective), and the picture thus produced is viewed as an original object through another lens or set of lenses (the ocular or eyepiece). By means of this instrument the observer is enabled to approach very close to the object, while the field of vision is greater than with the simple microscope.

II.—CELLS AND CELLULAR TISSUE.

1. Anatomy of Cells.

Cellular tissue (Fig. 2) is generally called Parenchyma (παρενχυμα, through, and ἐγκυμον, anything poured in—applied to tissue), and it also receives the names of Arcolar, Utricular, and Vesicular tissue. It exists more or less in all plants, and abounds in fleshy roots, stems, and leaves, and in succulent fruits. It constitutes the pith and outer bark of trees, and the central part of rushes. Chinese rice-paper consists of the central cellular tissue of Aralia papyrifera, cut into thin sheets, which show structure under the microscope. By cultivation, the turnip, carrot, cabbage, and other esculent vegetables, acquire much cellular tissue, and become tender and succulent. The bladders or cells of which the tissue is composed, vary in size. In a cubic inch of a leaf of the carnation, there are said to be upwards of three millions of cells. They are frequently seen \( \frac{1}{4} \)th, \( \frac{1}{8} \)th, and \( \frac{1}{32} \)th of an inch in diameter. In some of the cucumber tribe, and in the pith of aquatic plants, large cells, \( \frac{1}{2} \)th and \( \frac{1}{6} \)th of an inch in diameter, occur. Mohl says, that the general average diameter of cells is \( \frac{1}{5} \)th to \( \frac{1}{10} \)th of a line; that of the cellular spores of Fungi and of the yeast cells, is \( \frac{1}{10} \)th of a line; while in succulent plants, and in the pith of the Elder, it rises to \( \frac{1}{2} \)th of a line or more.

Cells are either surrounded by a simple thin membrane, or by thickened walls. The thickening of the walls of cells takes place by a deposit of woody matter on the inside, as seen in the microscopic structure of the hard shell of the Coco-nut and Piassaba fruit, in the stone of the peach and cherry, and in the seed of the Ivory and Date palms. Occasionally, rounded portions of the cell-wall are left uncovered by deposits, giving rise to the formation of Porous, or Dotted, or Pitted cells (Fig. 5); while, at other times, the thickening matter assumes the form of a ring or of a spiral coil, thus constituting Annular (Fig. 6) and Spiral cells (Fig. 7). In Vaucheria, Charophora, and other sea-weeds, peculiar reproductive cells called spores are met with, having thread-like filaments (Fig. 8) which exhibit a vibratile motion resembling that of the cilia of animal mucous membranes. In Equisetum or Horsetail, there are reproductive cells, surrounded by two filaments, with thickened clavate or club-shaped extremities (Fig. 9), which are remarkably hygroscopic, and exhibit movements when breathed upon.

When formed of cells composed of a homogeneous or uniform membrane, the tissue is called Membranous cellular tissue; when of spiral cells it is denominated Fibrous cellular tissue, or Irenenchyma (Ires, fibres). Elongated cells or tubes, with pointed extremities, when united together, form the tissue called Prosenchyma. The membranous walls of some elongated cells occasionally unroll in a spiral manner. Spiral cellular tissue exists in many Orchids; also in the cells of Sphagnum, the hairs of Cactaceae and the seed-coat of Cassurina, in the outer covering of the seed of Collomia linearis, and of the fruit of Salvia verbenaca, or wild Clary. The spiral cells in the last two mentioned cases, when placed in water under the microscope, exhibit interesting movements, owing to the solid spiral fibre rupturing the softened membrane of the cell, and expanding in all directions. The spongy elastic character of the outer cellular covering of the roots of tropical Orchids and Araceae, of the sepals of Illicium verticillatum, of the pericarp of Cachrys Morisoni and C. odontalgica, and of the ribs of the fruit of Æthusa Cynapium, is due to the presence of spiral cells. In the reproductive cells of Liverworts, spiral fibres called Elaters are found. Reticulated or netted cells, caused by fibres forming a sort of mesh or network, occur in the wing of the seed of Swietenia, in the pericarp of Picridium tincturatum, and P. vulgare, in the seed-coat of Cucurbita Pepo, in the parenchyma of the leaf of Sansevieria guineensis, and in isolated cells of the pith of Rubus odoratus, and of Erythrina corallodendron.

Cells differ in form according to the mode in which they are aggregated. They are frequently rounded or spherical, at other times they present angular or elongated forms, such as pentagonal or five-angled, hexagonal or six-angled, prismatic square, fusiform or spindle-like. When the cells are so placed as to touch each other on every side, the Parenchyma is called complete. This is seen in the dodecahedral or twelve-sided (Fig. 2), and prismatic Parenchyma of pith, and in the flat tabular Parenchyma of the outer corky bark of trees. When the individual cells touch each other only at certain points, the Parenchyma is incomplete. This occurs in the case of the spherical and elliptical cells (merenchyma, popov, to revolve) of succulent plants, such as the Cactus, and in the stellate or star-like cells (actinenchyma, dextra, a ray) of the Rush, Callitriche verna, and Bean (Fig 10). In incomplete Parenchyma spaces are left between the cells, which are either large circumscribed cavities called Lacunae, or continuous passages called Intercellular Canals. The spaces between the cells are filled either with fluids of different kinds, or with air. Occasionally the intercellular

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1 See figure and description in Balfour's Class-Book of Botany, p. 1072. 2 For the use and construction of the microscope, see article Microscope. See also Quckett on the Microscope. Balfour's Class-Book of Botany. Bennett's Lectures on Clinical Medicine. Schacht on the Microscope. Botany. substance assumes a thickened or corky consistence, and unites the cells firmly; and it appears to be sometimes prolonged over the surface of the plant in the form of a cuticular covering.

2. Physiology of Cells.

When we consider that cells are of universal occurrence in the Vegetable Kingdom, and that they constitute, in some instances, the entire structure of plants, we can easily understand their importance in a physiological point of view. They are capable of carrying on all the functions of plant-life. The life of an individual cell may represent that of the entire plant. In the case of a unicellular Alga, as Palmella (Fig. 11), we meet with a simple cell which absorbs nutriment from the atmosphere and the soil, and forms certain organizable matters, some of which are employed in building up its texture, while others are secreted or set apart for ulterior purposes in its economy. Those actions are frequently accompanied by an evident movement of fluids and granules. In the progress of time cellules are developed in the interior of the cell, which are discharged as independent cell-plants capable of performing all the function of the parent cell. In other instances, the original cell gives origin to the new cells, either by means of nuclei (Fig. 12), or by a constant process of division (Fig. 13), until at length a cellular plant is produced consisting of numerous cells variously arranged. In higher plants, cells undergo transformations fitting them for their special functions. Vital operations are carried on in all plants by means of cells, the constitution and functions of which vary according to the nature of the plants and the position in the scale of organization which they occupy. In the higher classes of plants, certain cells are concerned in the secretion of organizable products, which are elaborated by others into new tissues. The life of plants consists in the regular action of different kinds of cells, which are concerned in the formation of new organs and of new products. In cells there are observed the absorption and movements of fluids, the elaboration of these by exposure to air and light, and the formation of new cells.

In its early state a plant consists of one or more cells. These appear to be produced from a viscid substance of an albuminous nature, to which the names of Protoplasma, Cytoplasmata, and Vegetable Mucus have been given. This substance is first homogeneous, then granular; and according to some exhibits minute fibres. It is coagulated by alcohol, and coloured yellowish-brown by iodine. It is considered as the earliest stage of vegetable tissue, and as being endowed with a certain formative power. By Barry, the organizing matter is called Hyaline (glauc, glass), from its pellucid nature. Some say that in this protoplasm nuclei are developed which give origin to cells; others state that the nitrogenous matter becomes at once divided into cell-like cavities, each of which produces a covering of cellulose for itself. The formation of nuclei or cells in a protoplasmic matrix, without the influence of another cell previously existing, may be called extra-cellular.

When a cell has been produced, we can then trace some of the stages by which new cells are formed. This process is called cell-development or Cylogenesis (κύτος, a cell, and γένεσις, origin), and it has engaged the attention of many able physiologists. There appear to be four modes in which vegetable cells are multiplied, viz., by nuclei, by division, by gemmation, and by conjugation. New cells originate in the protoplasmic fluid contained in a parent cell by a process of intra-cellular formation. The new cells may either proceed from a nucleus, or, as Schleiden calls it, Cytoblast (βλαστός, a germ); or they may be formed at once in the protoplasm. In the former case, the nucleus becomes as it were the centre of vital action, and on one side of it a bladder-like vesicle arises (Fig. 14, b). This original vesicle is bounded by a protoplasmic membrane, which ultimately becomes covered with a deposit of cellulose. The protoplasmic membrane forms the inner lining (primordial utricle of Mohl) of the new cell, and to it all the subsequent vital actions of the cell are referred. The nucleus either remains in the cell-wall, or it is absorbed. The newly-formed cell contains a formative fluid in which nuclei are produced, which, in their turn, give origin to other cells. Besides a nucleus, there are seen occasionally in cells very minute bodies called nucleoli, which some consider as being concerned in forming the wall of the nucleus. The nuclear formation of cells has been fully illustrated by Schleiden in the case of the Embryo plant. According to Mohl the nucleus is in the centre of the cell, and is attached to its walls by filamentous processes of protoplasm, as seen in the hairs of Tradescantia. When no nucleus is present, the protoplasm at once forms cells. This is called non-nuclear or free cell-formation. In both instances the formation of new cells takes place in the interior of previously formed cells. In progress of increase, nucleated and non-nucleated cells cause absorption of the walls of the parent cell, which finally disappears. It sometimes happens that the nucleus itself divides into two by a contraction in the middle, and each of its parts gives origin to cells. In this way a rapid multiplication of cells takes place. In Figure 14, b, there is represented a parent or mother cell, containing two nucleated cells in its interior. These gradually increase, cause absorption of the walls of the parent cell, and become free. In Figure 14, a, a parent cell is shown enclosing five nucleated cells.

After a cell is formed, we often remark that its contents divide into two or four parts. This is accomplished by the folding inwards of the protoplasmic inner lining, the primordial utricle of Mohl. Each division forms for itself a covering of cellulose. These newly-formed cells increase, cause absorption of the walls of the parent or mother cell, and separate from it as distinct cellular formations capable of going through the same process of division. Sometimes a cell divides into two or more parts, each of which becomes a separate cell, without any destruction of the walls of the original one, as shown in Figure 15. This is accomplished by a similar folding of the inner lining, and a subsequent formation of cellulose in each division, but it differs from the previous method of division in the circumstance that the walls of the parent cell remain without being absorbed. These modes of cell-multiplication are called fissiparous, or merismatic (fissum, cleft, peporus, division).

Cells are also produced by a process of budding; in other words, by a continuous growth from various parts of pre- Botany.

Previously formed cells. A cellular protuberance or mammilla appears either at the apex or at the sides of these cells, which elongates and ultimately divides by a partition or septum into two, one of which is arrested in its development, and the other goes on elongating and dividing. In this way a continuous row of cells is produced, as in certain Algae and in the Yeast plant (Fig. 16), or a branching filament, as in some kinds of Confervae (Fig. 17), or moniliform Fungi (Fig. 18), or a flattened thallus composed of interlacing cells,

The fronds of a species of Lycopodium (L. squamatum or Selaginella convoluta), from Brazil, curl inwards in the dry season, so that the plant appears like a brown ball, and during the wet season they spread out so as to cover the soil. The plant called Rose of Jericho (Anastatica hierochuntina) shows a similar hygroscopicity in its pod; and some of the Cape species of Mesembryanthemum open their seed vessels when moisture is applied. The spores or germs of Horse-tails (Equisetum) are provided with cellular clavate filaments (Fig. 9), which contract and expand under the influence of moisture and dryness, and thus assist in placing the germ properly in the soil. These Equisetum spores are interesting objects under the microscope, and their movements are seen by breathing upon them. Hairs, which are composed of cells, also show hygroscopic properties.

Liquids pass through the walls of cells by a process of imbibition. Thin-walled cells take up fluids very rapidly. To the movement of fluids through membranes of different kinds Dutrochet has given the names of Endosmose (εσω, inwards, and ὀπος, impulsion), or inward movement, and Exosmose (ἐκω, outwards), or outward movement. These movements take place both in living and in dead tissue, and they are influenced by the nature of the fluids and of the membrane. The fluids on either side of the membrane must differ from each other in density, and they must have an affinity for the interposed membrane, and for each other. By the endosmotic process, a thin liquid passes in large quantity and with great force through a vegetable or animal membrane, in order to mix with a denser liquid, while the latter passes outwards in small quantity by a slower exosmotic movement. If a unicellular plant, as one of the cells of the Yeast plant, is placed in a dense liquid, the contents of the cell pass outwards rapidly, and the cell becomes more or less collapsed; if, on the other hand, it is put into a thin liquid, the reverse takes place, so that the cell is distended.

The cells of plants contain liquids of different densities, and hence these movements must be constantly taking place, so as to cause an interchange of their contents. The bursting of the seed-vessel of the Elaterium (Echaliun purgans), and of the Balsam (Impatients), is traced in part to the distension of cells by endosmose, which causes a curvation in the parts and an ultimate rupture. It must, however, be borne in mind, that endosmose is modified in the living plant by the vital actions going on in the cells, and that it is to these actions we must refer the continued movements of fluids through the cell-walls.

The endosmotic phenomena may be illustrated by means of a tube of glass, containing syrup or a saturated solution of salt, the end of which is covered by a membrane, such as a piece of bladder, and then placed in water. In this case the water will enter in such quantity into the interior of the tube, through the membrane, that the fluid will rise. With a membrane about 1-6 inch in diameter, a tube of about 1-12th of an inch, and syrup of density 1-083, the fluid rose, according to Dutrochet, more than an inch and a half in an hour and a half; when the syrup had a density of 1-145, the fluid rose nearly three inches; and when the density was 1-228, the rise was four inches. The force with which the movement takes place is very great. Dutrochet estimated that in the case of syrup of density 1-3, the force of endosmose was equal to the pressure of 4½ atmospheres.

In many cells there is observed a distinct motion of fluids and granules. Schleiden thinks that this takes place in all active formative cells at a certain stage of growth. Moll looks upon it as a universal phenomenon, and says that it is connected with the protoplasm, and not with the watery cell-sap. This intra-cellular movement or circulation is seen in many aquatic plants as well as in certain hairs. It has received the names of Rotation and Gyration. It is confined to individual cells, and its direction is more Botany.

In Characeae (Fig. 21) this spiral intra-cellular movement is observed easily under a moderate microscopic power. During the healthy state of the plant, a constant motion of fluid containing granules takes place, the current passing obliquely up one side, changing its direction at the extremity, and flowing down the other side. The stream takes a spiral course, and the ascending and descending currents are bounded by transparent spaces which appear to be caused by the adhesion of an internal membranous sac to the outer envelope. The space between the outer and inner wall is thus divided into two cavities, which communicate with each other at the ends of the cell. The fluid does not pass from one cell to another, and if one of the long cells is divided by a ligature, a separate movement is seen in each division. Rotation continues for some days in detached cells placed in water.

In the cells of Vallisneria spiralis (Fig. 22), an intracellular movement takes place, and is easily seen under the microscope by laying a portion of the leaf in water, and making a slanting section of the end of it, so as to render the object more transparent by transmitted light. If the movement is not visible, the leaf may be immersed for a short time in water of the temperature of 70° or 80°. The piece of the leaf should always be prepared for an hour before it is exhibited. In the cells there are numerous green chlorophyll grains, some starch granules, and an occasional large nucleus, which are carried with a mucilaginous fluid round the interior of the walls of each cell, as represented in Fig. 23. This movement is seen not only in the cells of the leaf, but also in those of the root, flower-stalk, spathe, and calyx. The movement takes different directions in different cells, but it seems to keep the same course in any given cell; for if stopped, it resumes the same direction. The motion continues for many days in a detached piece of the leaf when kept in water. The rapidity of the movement varies from half an inch to five inches per hour.

In Vallisneria the motion ceases entirely at about 45° Fahr., while in Chara it goes on at a lower temperature. A moderate heat quickens the circulation, but if above 150° the motion ceases. It is said to go on even in darkness, and the presence of green granules does not appear to be necessary, for it is seen in the transparent roots of Vallisneria. Prussic acid, solutions of opium, of acetate of lead, and of corrosive sublimate, alcohol, acids, and alkalies, cause cessation of the movements. Similar motions are seen in many other aquatics, more especially in the cells of Anacharis Alsinastrum, a plant which seems to have been introduced into Britain from America, and is now naturalized.

The cause of these intra-cellular motions is obscure. They appear to be connected with the nourishment of the cell and the process of cytotaxis. Some have attempted to account for them by physical causes, but the explanations given are very unsatisfactory. Certain authors have referred the phenomenon to endosmosis depending on different densities in the cell contents, while electrical agency has been called into requisition by others. Amici thinks that in Chara the rows of chlorophyll-granules which line the walls of the cells exercise a galvanic action upon the sap, and thus give rise to the motion. The action of the nucleus has also been thought to account for the phenomenon. It is not connected with the general circulation of the sap, but is a special movement in individual cells. As yet no good explanation has been brought forward, and all we can say is, that the movements are of a physico-vital nature.

Some cells connected with the lower tribes of plants move about in a liquid medium. Species of Oscillatoria have an undulating movement, and when placed in water in the field of the microscope, they seem to pass from one side to the other. Their elongated filamentous cells sometimes twist, and then project themselves forward by uncoiling. Oscillating movements are also seen in species of Pleurosigma and other Diatoms. In many Algae the cellular spores are surrounded by vibratile hairs called cilia (Fig. 8), which continue to move for some time in fluid after the spore (zoospore) has been discharged from the plant. The ciliary motions cease when the spore begins to sprout.

III.—VESSELS AND VASCULAR TISSUE.

1. Anatomy of Vessels.

The vessels of plants which collectively form vascular tissue or Angiochyma (ἀγγειον, a vessel) may be considered as differing from cells chiefly in their length. They are closed tubes tapering to each extremity. Their walls are composed of the chemical matter called cellulose in a membranous form, and they are thickened and altered in various ways by the formation of deposits in their interior.

Woody Tissue.—This is composed of thickened tubes or elongated cells, with conical extremities overlapping each other, as seen in Figure 24. The tubes are said to be fisiform or spindle-shaped, and the tissue has received the name of Pleurochyma, from a Greek word πλευρα, meaning a rib, on account of the support which it furnishes to the stems and leaves of plants. The woody portion of trees and shrubs, and of all the ordinary flowering plants, consists in part of this tissue. It exists also in the inner bark, and in the veins of the leaves. The materials used for ropes and cordage, linen, certain Indian muslins, mummy cloth, and mats, consist of the woody fibre of plants from which the more delicate tissues have been removed by maceration in water. Flax or lin is thus procured from the bark of Linum usitatissimum, hemp from Cannabis sativa, New Zealand flax from Phormium tenax, Pita flax from Agave americana, Sun-hemp from Hibiscus cannabinus, and bass or bast from the common Lime or Linden-tree. Fibres are also procured for manufacture from the Pine-apple plant (Ananas sativa), from Yucca gloriosa, from Boechneria nivea, which yields the Chinese grass fibre, from most of the plants belonging to the mallow and nettle tribes, and from some of the leguminous plants, such as Crotalaria juncea which supplies a kind of Bengal hemp. If the maceration of the fibre is carried to a great extent, a pulp is formed from which paper is manufactured. Pleurerenchyma does not occur in cellular plants, such as Lichens, Sen-weeds, and Mushrooms. The tissues of these plants speedily disappear under the action of water, and hence, perhaps, the reason of their rarity in a fossil state. In the very young state woody tubes are delicate, and it is only in proportion as they attain maturity that their walls acquire a thick consistence. This depends on the formation of layers of cellulose, which have received the name of ligneous matter. In the sap-wood of ordinary trees the woody tubes are thickened in their walls, but are pervious; while in the heart-wood they are rendered solid by the deposited matter, which is often variously coloured. Some of the fully-formed woody tubes, when cut across, exhibit distinct zones or circles of ligneous deposit. The diameter of the woody tubes varies from \( \frac{1}{3} \) th to \( \frac{1}{2} \) th of an inch.

**Punctated or Disc-bearing Woody Tissue.**—This kind of woody fibre or pleurerenchyma is seen in firs and other cone-bearing trees. It is sometimes called glandular woody tissue. When a section is made in the direction of the rays running from the centre to the circumference of the stem, the fibres exhibit under the microscope discs or large circular dots, which are saucer-like spaces or depressions on the walls of the tubes. They are seen in Fig. 25. When two woody tubes lie together face to face, the depressions or hollowed-out spaces on each of them are applied like two watch-glasses leaving lenticular cavities, which are sometimes filled with air. When viewed by transmitted light under the microscope, these appear like circular discs. The dot seen in the centre of the disc depends on a portion of the wall being thinner than the rest. In Fig. 26 this structure is seen in a magnified form. The walls of the fibres or tubes are marked \( p_f \), the internal cavity of the fibre \( c_f \), and the lenticular cavities \( e_l \) formed between the two contiguous fibres, \( r_m \) being one of the cellular rays proceeding from the centre to the circumference, interposed between the walls of two contiguous fibres. In the case of some fossil woods, pieces of silica like double-convex lenses have been removed from the cavities. The discs are in single, double, or triple rows (Figs. 27, 28). When there is more than one row, the individual discs in the rows are either at the same level, that is, opposite to each other (Fig. 27), as in the case of ordinary pines; or they are at different levels, that is, alternate with each other (Fig. 28), as in Araucaria. Sometimes spiral fibres are seen between the discs. Woody tissue with discs, but without the central dot, occurs in many plants, as in Drimys Winteri,* and Illicium floridanum.

**Dotted or Pitted Vascular Tissue.**—The vessels, or, as Pl. CXL they are often called, Ducts, forming this tissue, are usually continuous tubes of a larger size than the other vessels of plants (Fig. 3), and, presenting often broad or oblique extremities in place of pointed ones like other vessels. Their dotted or pitted appearance depends on the mode in which the encrusting matter or cellulose is formed inside. This matter in place of being deposited equally over the whole surface of the membrane, as in ordinary woody fibre, leaves rounded uncovered spots at various intervals; and these, when viewed by transmitted light, appear from their thinness to be perforations or holes. Hence the name Porous, which is often applied to these vessels. In old dotted ducts it is occasionally found that the thin membrane of the dots or pits has been absorbed, and actual perforations have taken place. Dotted vessels frequently exhibit contractions at intervals, giving rise to a jointed or bead-like appearance. In such cases, as in Figure 29, they are seen to be formed of dotted cells placed end to end, with the partitions between them obliterated, so as to form continuous cylindrical and sometimes branched tubes. Occasionally they seem to be formed, as in Rhubarb, by a filling up of the interspaces between fibres, until a small pit only remains; or, as in Alnus serrulata, by a number of lines arranged at first like those of a ladder, and then united by transverse ones forming a grating, the angles being finally filled up and rounded; or, as in Populus tremuloides, by a uniform deposit over the whole membrane. In the Elm and Lime the dotted ducts have sometimes spiral fibres ramifying between the dots. The membranous walls of dotted vessels occasionally unroll in a spiral manner. Dotted ducts are found in the wood of trees, and they constitute the large rounded openings which are seen in the transverse section of the stems of Oak, Poplar, Willow, &c. They also abound in the Bamboo (Fig. 4), and in other plants of rapid growth. The names of Bothrenchyma and Trachrenchyma, given to this tissue, are derived from Greek words βόης and τράχης, signifying a pit.

**Spiral vessels.**—These form the tissue called Trachenchyma (τράχης, rough) on account of its resemblance to the tracheae or air-tubes of animals. They are tubes tapering to each extremity, and having their membranous walls strengthened by the formation of elastic spiral fibres within (Fig. 30). They vary from \( \frac{1}{3} \) th to \( \frac{1}{2} \) th of an inch in diameter. When lying together the vessels overlap each other at their extremities, and occasionally, by the absorption of the membrane, perforations of their walls take place, so as to establish a communication between two contiguous tubes. The fibres are usually rounded and simple; but sometimes two or more are combined so as to form a flat band. These flat ribands, consisting of fibres which vary in number from 2 to 25, or more, are met with frequently in the stems of Bananas and Plantains, and in the shoots of Asparagus. The spirals in such cases are called compound, and the vessels Pleiotracheae (πλείων, more). The spiral fibres have such tenacity, that when the vessels are ruptured they can be pulled out and separated from the inside of the membrane. This capability of being unrolled characterizes the fibre of true spiral vessels. On breaking the young shoots or leaf-stalks of the Geranium, Strawberry, and Rose, or the leaves of the Hyacinth, Amaryllis, and Banana, and pulling the parts gently asunder, the fibres can be easily seen in the form of a fine cobweb. When the aerial stems of the Banana and Plantain are cut across, the spiral fibres may be pulled out in large quantity so as to be used for tinder.

The coils or volutions of the fibre are said to be in general left-handed, that is, turning to the left of a person supposed to be in the axis. In the garden lettuce vessels are met with, some having the fibre turning to the left, others to the right. In the scarlet bean the coils of the fibres are left-handed, while the plant itself turns to the right in twining. Spiral vessels are abundant in young plants and shoots, while in the hard stems of trees and shrubs they chiefly surround the pith.

Modifications of Spiral Vessels.—The spiral vessel is the type of what is called the Fibro-vascular tissue, or that tissue which is composed of vessels having membranous walls strengthened by fibres of some sort. In their perfect condition the vessels have a complete spiral or cork-screw-like coil inside, which is elastic, and can be unrolled. In different plants, however, and in different parts of the same plant, the spiral vessel undergoes certain modifications and changes. Sometimes, as in ferns, the spiral fibres become united to the membrane so that it cannot be unravelled. This constitutes what is called the Closed spiral. At other times the fibre is broken up into rings, reticulations, bars, or dots. These changes take place in the progress of growth, (Fig. 31) and their various stages may be traced in the vessels of such plants as the garden balsam or melon.

Annular (annulus, a ring) vessels are those in which the fibre is in the form of rings (Fig. 32). These rings in Mammillaria quadrispina, and in some other plants of the Cactus tribe, are very deep, and leave only a small hole in the centre of the vessel. Annular vessels are from $\frac{1}{4}$th to $\frac{1}{8}$th of an inch in diameter. Reticulated (reticulum, a net) vessels (Fig. 33) have interlacing fibres on the membrane, while in Scalariform (scala, a ladder) vessels (Fig. 34) the fibre is so broken up as to appear in the form of bars or lines like the steps of a ladder, whence their name. The entire walls of some scalariform vessels are capable of being unrolled in a spiral manner. In Ferns we meet with scalariform vessels which assume a prismatic form. In place of lines, the fibre is in some instances so broken up as to appear in the form of dots or opaque points. The appearance of bars, dots, and reticulations, may sometimes be traced not to a thickening of the membrane by means of fibres, but to an actual thinning of the membrane, such as has been already noticed in the case of dotted ducts.

Laticiferous Vessels.—These vessels (Fig. 35) consist of long branching tubes or passages, having a diameter of about $\frac{1}{4}$th of an inch, forming, by their union, an anastomosis or net-work, like the veins of animals. They receive their name from containing a fluid called Latex, of a granular nature, often milky or coloured, and well seen in the India Rubber and Gutta Percha plants, the Mudar plant, the Cow-tree, Spurges, Dandelion, Lettuce, Chicory, and Celadine. It frequently contains a large quantity of caoutchouc. The Latex exhibits movements which have given origin to the name Cineschyma (ciner, to move), applied to Laticiferous vessels by some authors. When fully formed, the vessels of latex exhibit in their course contractions and dilatations of an irregular kind. They are considered by some as composed of cells placed end to end, with their partitions more or less completely absorbed; while others look upon them as inter-cellular canals lined with a special membrane. These vessels are found especially in the bark and leaves of plants. The milky sap of Euphorbia phosphorea, according to Martius, is luminous.

2. Physiology of Vessels.

We have seen that the plant, in its earliest stage of development, consists entirely of cells. It is from them, accordingly, that the other structures are formed. Some cells become elongated, so as to form fusiform tubes, the walls of which are thickened and strengthened by deposits of different kinds, and thus give rise to woody tubes, dotted vessels, and fibro-vascular tissue. In connection with these vessels are observed nucleated cambium cells, which appear to be concerned in their development. Barry maintains that in every instance in which fibres are present in tissues, he has noticed filaments of a similar nature in the earliest state. Agardh has recently stated that fibres are the origin of the tissues, and that the cell-walls are made up of bundles of solid fibres interwoven together. The tubes forming the wood (Fig. 24) are pervious to fluids in their young state, but their walls soon become thickened by deposits of lignin, and in the heartwood of trees their cavities are obliterated. This filling up of the tube takes place often in a concentric manner, and when it is completed the active life of the cell or tube may be considered as having terminated. The dotted or porous vessels (Fig. 3) constituting bothrenchyma, do not exist in all vascular plants. Thus they do not usually exist in Conifers. These vessels appear to be employed in the rapid transmission of fluids, and they are so constructed as to unite the utmost possible strength with the greatest lightness.

The functions of the fibro-vascular tissue (Figs. 30–34) have been long a subject of dispute. Early authors, such as Grew and Malpighi, considered them as tubes for the transmission of air, probably from their resemblance to air-tubes of animals. Hales mentions that air-bubbles arose from the vessels of the Vine when cut, and Bischoff, in his Dissertation on the Functions of the Spiral Vessels, says that he distinctly observed air to come from the spirals of Cucurbita Pepo when the stem was cut across with a very sharp knife, as well as when the vascular bundles were placed under water and gently pressed. During the day the air was found to contain 27.9 to 29.8 per cent. of oxygen. When the cut stem was inserted in coloured solutions, he found that the fluid in these circumstances entered the spiral vessels as well as the other tissues. The recent experiments of Hoffmann confirm in a great measure these observations. He found that in Monocotyledons and Ferns, spiral vessels, and those allied to them, such as annular and scalariform vessels, usually contained air in their normal condition; but if there was a rapid and copious entrance of sap, then the fibro-vascular tissue took up liquids as well as air. When the roots were cut across and immersed in water, then the liquid passed into all the tissues, including the spirals. From all the observations made, it would appear that spiral vessels and their allies are receptacles for gaseous matter formed in the course of the movement of the sap.

Laticiferous vessels (Fig. 35) are distinguished from others by their branching and anastomosis. Most authors believe that they contain the elaborated sap which has been exposed to the influence of air and light. The fluid contained in these Botany, vessels is sometimes clear and transparent; at other times opaque, from the presence of granules of resin, caoutchouc, and other matters. In plants with milky and coloured latex, as the India Rubber plant (Urostigma elasticum), the Gutta Percha tree, Dandelion, Euphorbia, and Celanidine, when examined under the microscope, evident movements have been perceived in the laticiferous vessels. In making this examination, it is necessary to fix upon a more or less transparent organ, and to examine it while still attached to the plant, so as to avoid all sources of fallacy. In the calyx of Celanidine (Chelidonium majus) the orange-coloured fluid contained in the laticiferous vessels can be distinctly seen moving with great rapidity, so as to resemble in many respects the appearance presented by the circulation in the web of a frog's foot. In the stipule of the India Rubber plant, a similar motion, but usually slower and less apparent, may be detected without injuring the plant. These movements were noticed by Schultz, and were called by him vital. Mohl and others have recently attempted to show that the movements are merely caused by injury done to the tissues in submitting them to microscopic examination. But this will not account for those cases where the motion of the latex was seen in an organ without detaching it from the plant. Moreover, it is by no means difficult to distinguish between the continuous rhythmical motion in these vessels and that caused by pressure or by injury. When the stipule of Ficus, still attached to the plant, is laid gently on a glass plate under the microscope, we may, by applying artificial pressure, show that the oscillation thus caused is different from the circulation in the vessels. The movement in the laticiferous vessels has received the name of Cycloitis (κύκλωσις, motion in a circle). It seems to take place in all directions, the currents, as shown in Fig. 36, running in contrary directions in contiguous vessels. The movement is said to be most vigorous in parts which are in the progress of development. It is promoted by the application of heat, and it is checked by cold and by an electric shock. Carpenter considers it as analogous to the capillary circulation in animals. It is not caused by a vis a tergo, because it is by no means constant in its direction, and there is no organ to supply a propelling force; and it cannot be attributed to a vis a fronte, like that which operates in causing the sap to ascend from the roots to the leaves. Moreover, it goes on for some time in parts detached from the rest, where neither of these powers can be exerted.

There is no evidence of contraction in the vessels themselves to account for the phenomenon. It seems to be a peculiar vital movement connected with formative actions, and attributable to affinities existing between the tissues and the fluids concerned in nutrition.

IV.—CONTENTS OF THE ELEMENTARY TISSUES.

It is not proposed at this place to give an account of all the substances which are found in the tissues of plants, but simply to notice a few of the more evident contents of cells and vessels. Some substances are found generally in the cells and vessels of all plants, while others are very limited in their distribution. To the former class belong cellulose, lignin, starch, gum, sugar, oils, colouring matter, and certain nitrogenous and saline compounds; to the latter belong alkaloids and some special secretions.

Cellulose.—This is an essential part of the structure of cells and vessels. It is in many respects allied to starch, and is changed into starch by the unaided action of heat, or by sulphuric acid, or caustic potash. When iodine is applied to it, it becomes yellow, and if sulphuric acid is added, a blue colour, like that of iodide of starch, is produced. Cellulose was long considered as peculiar to vegetable tissues, but it has been recently detected by Schmidt, Löwig, and Kölliker, in the tunics of ascidia and other molluscous animals. The thickening of the cellular membrane is accomplished by the deposition of layers of encrusting matter, to which the name of Sclerogen (σκληρός, hard) or Lagenin has been given. This substance may be looked upon as a modification of cellulose. It is frequently seen in the form of distinct concentric layers, which vary in their composition in different circumstances. The hard cells in the stone of the peach, and in the shells of other fruits and seeds, consist of cellulose, with deposits of lignin. So also woody fibre, the encrusting matter of which varies in hardness and colour in different trees and shrubs. The spiral threads, rings, and bars, in the membrane of cells and vessels, consist apparently of two layers, one being cellulose, the other woody matter. Cork is a nitrogenous substance, which, next to cellulose, according to Mitscherlich, is the most important constituent of the cell-wall. It occurs in a marked degree in the outer bark-cells of many trees, and it is also found in other plants, such as in potatoes. In the latter the cork-cells do not contain starch, and they are thus distinguished, as well as by chemical properties, from the cells made up of cellulose. Cellulose, corky substance, and fatty matters, seem to be found in the same cell; and when the cellulose has been absorbed, the corky substance alone remains. It forms the outermost part of the cell-wall, and unites the cells together.

Starch.—Is one of the substances found in great abundance in the cells of plants, where it is stored for the purposes of nutrition. It is composed chemically of Carbon and the elements of water (Hydrogen and Oxygen), its formula being C_{12}H_{22}O_{11}. It is not found in animal tissues, although a substance isomeric with it is stated to have been detected in them by Gottlieb. A distinguishing character of starch is the blue colour which it assumes on the addition of iodine. It occurs in fine grains, more or less oval or rounded, which vary in diameter from the 4000th to the 240th of an inch. The individual grains either lie distinct from each other in the cells, as in the potato, wheat, and peas (Fig. 37), or they are aggregated so as to form compound grains, as in West Indian Arrow-root, and Portland Sago procured from Arum maculatum.* Grains of starch frequently present at one end a spot called the hilum, which is seen in the grains given in Fig. 37. It is a concavity or nucleus over which successive layers have been deposited, giving rise to the striated appearance seen in potato starch. Starch is accumulated in the internal, and starch often in the subterranean parts of plants. It occurs abundantly in fleshy roots, and in stems, as well as in seeds and fruits, and is easily separated by washing. The ordinary cultivated grains yield starch in considerable quantity, so also do the Potato, Arrow-root and Cassava plants,* the Sago-palms, and *Pl. CXIII. Banana fruit. That procured from the Arrow-root plant, Fig. 1. (Maranta arundinacea) consists of dull white grains, while that from the potato, and from various species of Canna supplying tous-les-mois, is in the form of large shining particles. Sago and Tapioca are granulated forms of starch, the former being procured from the cells of various species of Sagos and Metroxylon, the latter from the Cassava plant. The existence of starch in the bark and young wood of trees, such as the Birch and Pine, renders them useful as articles of food in cold countries. Lichenin is a form of starch existing in the cells of Iceland moss and other lichens; while Inulin is the starchy matter supplied by the roots of the Dahlia, Dandelion, and Eleocharis. By the action of prolonged heat, as well as by the addition of diluted sulphuric acid, and of malt, starch is converted into a soluble gummy substance called dextrin. The same change we shall find occurs during germination or the sprouting of the seed.

Gum.—Is another substance contained in vegetable tissues. When pure, it is clear, soluble in water, and also in dilute acids, but not soluble in alcohol or ether. It is one of the forms through which vegetable matter passes in being applied to the purposes of plant life. It exists largely in the vegetable juices. From the bark of many trees it is procured in the form of an exudation. Two well-marked kinds of gum are met with: Arabine, soluble in cold water, constituting the chief ingredient of gum-arabic, procured from various species of Acacia; and Cerasine, insoluble in cold water, and readily soluble in boiling water, constituting the gummy secretion obtained from the cherry and plum. A substance called Bassorin, or vegetable jelly, is found in Tragacanth, the roots of some Orchids, as well as in Carageen (Sphacelococcus crispus), and other sea-weeds. It is allied to gum, but differs in swelling up and becoming gelatinous when mixed with water. Another jelly-like substance called Pectic acid exists in the juice of turnip, beet, and carrot, as well as in the apple and pear.

Sugar.—Occurs abundantly in the sap of plants. When pure, and in a solid state, this substance is crystalline, and soluble in water. It occurs, however, in an uncrystallizable form. There are two marked varieties of it. Cane sugar, procured from the sugar-cane, sugar-maple, beet, carrot, and many other plants; and grape-sugar, occurring in numerous fruits, as grapes, gooseberries, currants, peaches, and apricots. The formula for Dry Grape-sugar is $\text{C}_6\text{H}_{12}\text{O}_6$. During the sprouting of the seed, starch is converted into grape-sugar, and a similar change is induced by the action of malt, and of any ferment. A sweet substance (not a true sugar), called Mannite, is procured from the Mann's-ash, as well as from various sea-weeds, from species of Eucalyptus, and from the Dandelion.

The substances which have been noticed as occurring in the elementary tissues are important as organic products concerned in the growth and nourishment of plants. Some differences of opinion exist among chemists as to their exact atomic composition; it is sufficient at present to notice that they all consist of a definite proportion of carbon, united to oxygen and hydrogen, the elements of water. They are convertible into each other by the action of heat and of various chemical re-agents, and by the powers of vegetation. The ultimate composition of several of them is identical, and the difference of their properties, in such instances, seems to depend on differences in the arrangement of their atoms.

Another class of substances, found in the tissues of plants, and essential for the process of vegetation, consist of carbon and the elements of water, with the addition of nitrogen or azote. Hence they are called nitrogenous or azotized. They occur abundantly in the gluten of wheat flour. Schleiden includes them under the general name of vegetable mucus. The chief substances which enter into the composition of this nitrogenous matter are albumen, fibrine, caseine, legumine, and emulsine.

Nuclei.—The cells of plants, at some period of their existence, usually contain what are denominated nuclei or cytoplasm. The nucleus is a small rounded body resembling a minute cellule, which is either loose or attached to the walls of the cell containing it (Fig. 12). It frequently contains smaller bodies called nucleoli. The nucleus has an important function to perform in cell growth, as has been noticed under cytogenesis or cell-development, and after a certain period it frequently disappears.

Chlorophyll and Colouring Matters.—Chlorophyll or Phytochlor, is the matter which gives the green colour to plants. It is a coloured fatty or wax-like substance, which may be separated by the action of alcohol and ether. The green colour is associated with globules of various sizes, which are either free or united together. The globules of chlorophyll can be seen under the microscope in any of the green parts of plants. In delicate structures, such as the cellular tissue of mosses and liverworts, they are easily examined. The colour is only produced under the action of light; hence chlorophyll exists in the superficial cells of the parenchyma, thus differing from starch, which is produced in the internal and subterranean organs, whence light is excluded. It undergoes changes according to its state of oxidation; hence the tints which the green leaves acquire in autumn. There would appear, therefore, to be a colourless chlorophyll present in plants, which is acted on by light, oxygen, and other agents, so as to give rise to green, yellow, and red tints. Schleiden says, the yellow leaves in autumn contain proportionately more wax than the green leaves of summer, the yellow rind of the ripe fruits more than the green rind of unripe fruits. The tints of flowers depend either on variously-coloured insoluble globules, which are considered to be of a nitrogenous nature, or on soluble substances which have not been fully examined. Colouring matters not green are included under the name of Chromule.

Oily, Fatty, and Resinous Matters.—These are contained in cells and in special canals and cavities, called receptacles of secretion. The oils are either fixed or volatile; the former being divided into drying, fatty, and solid; while the latter are distinguished according as they consist of carbon and hydrogen alone, or of these elements combined with oxygen or with sulphur. Resinous matter occurs either in the form of fluid balsams, or of the various kinds of solid resin and pitch. In the rind of the orange and lemon, receptacles of oil occur. These are represented in Fig. 38, which is a vertical section of part of the rind of the orange, the reservoirs of volatile oil being marked n n. The cellular tissue of the rind is seen surrounding the oil cavities, and the cells are elongated and condensed, so as to form a compact tissue in the walls. Turpentine canals are met with in the bark of Pines; and Vittae or oil-canals in the fruit of Umbelliferous plants, such as the Coriander. In *Pl. CXXI., the fleshy covering of the fruit of the Olive, there are numerous oil-cells. The fruit of the Guinea-palm yields a solid oil called Palm oil. The dotted appearance of the leaves of the orange, myrtle, Eucalyptus, and St John's wort, depends on the presence of numerous cells or cavities containing essential oil.

As allied to these secretions, we may notice Caoutchouc, which is found in the milky juice of plants, especially those belonging to the Fig, Spurge, and Dogbane orders. The trees most prolific in this substance are, Siphonia Caoutchouc, Urceola elastica, and Urostigma elasticum. Gutta Percha is the concreted milky juice of the Tahian plant (Isonandra Gutta). Wax is also found in the tissues of plants, and it frequently occurs as a secretion on the stems, as in the Wax Palm, and on the surface of fruits, as in the bloom or glaucous secretion of the plum and the candleberry myrtle.

Air-Cavities.—Cells and intercellular spaces containing air are found in many aquatic and marsh plants, apparently with the view of rendering them buoyant (Fig. 39, a). In some cases they are regular in their formation, being surrounded by cells which are built up on a uniform plan in each species of plant, as in Pondweeds (Fig. 40, t). In other instances they are formed by the destruction or absorption of part of the cellular tissue, as in the case of many hol-

Raphides or Crystals.—Cells and vessels also contain various mineral and organic acids, combined with alkaline substances. The most important of these acids and alkalies will be noticed when considering the chemistry of vegetation, and the products furnished by different natural orders. At present we shall consider the composition of certain crystalline matters found in cells, to which the name of the Raphides (needle, a needle), has been given. These are present in greater or less quantity in almost all plants. They consist of oxalic, phosphoric, muriatic, sulphuric, and carbonic acid, in combination with lime, and they exhibit various forms. Crystals of phosphate of lime occur usually in the form of acicular crystals, varying from \( \frac{1}{10} \)th to \( \frac{1}{100} \)th of an inch in length (Fig. 41, r); to these the name of needles or raphides was originally given. Cells with clusters of raphides may be seen attached to the divisions between the cells in the Banana. Crystals of oxalate of lime assume an octahedral form, and vary from \( \frac{1}{10} \)th to \( \frac{1}{20} \)th of an inch in length (Fig. 42). They are abundant in the root of Turkey Rhubarb, to which they impart grittiness, and in Old-Man-Cactus they constitute 60 to 80 per cent. of the dried tissue.

The Squill bulb, and the bulb of the onion, exhibit raphidian cells, which are easily separated during the decay of the plants. In a single cell of the Poke (Phytolacca decandra), twenty to thirty crystals may be seen.

Siliceous matter occurs in the walls and cells, and enters into their composition. This is the case with Grasses and Horsetails, and, in a remarkable degree, with those peculiar organisms supposed by Ehrenberg to be Infusoria, but now referred to the vegetable kingdom under the name of Diatomaceae.

V.—INTEGUMENTARY SYSTEM.

The general Integumentary covering of plants consists of cells variously aggregated, and may be considered in connection with the elementary tissues. It has been divided into two parts—the Proper Epidermis, and the Outer Pellicle or Cuticle. The epidermis is formed of one or more layers of colourless thick-walled cells cohering together, so as to constitute a firm membrane, which can be pulled off from the subjacent tissue. The colour of the epidermis in general depends on that of the parenchymatous cells below, from which it can be separated as a colourless layer. Occasionally, however, the epidermal cells contain colouring matter, as well as waxy, siliceous, and calcareous substances. In the case of Orchids, it is not uncommon to find spiral cells in the epidermis covering their aerial roots. The epidermis covers all parts of plants exposed directly to the air except the stigma, which is formed of loose cells at the upper part of the pistil or central organ of the flower. The epidermis is sometimes much thickened, as in the Oleander and American Aloe, by being composed of numerous layers of cells, while at other times it is very thin. A delicate epidermis, called Epithelium, lines the internal cavities of certain organs, such as the ovary containing the young seeds. The boundaries of the epidermal cells frequently assume a waved or sinuous aspect (Fig. 44). The outer cuticle is a thin layer covering the true epidermis, and apparently formed from the cells of the latter. It may be merely a changed condition of the walls of these cells, or a modification of the inter-cellular substance which surrounds the cells. It forms the covering of hairs, as seen in Figure 43, which represents the cuticle of the cabbage with hairs, h, and it extends into certain openings in leaves called stomata (Fig. 43, s). In plants constantly under water, and in certain of the lower tribes, the cuticle is the only integumentary covering. The outer cuticle is considered by Mittererlich as a corky substance, which prevents the penetration of moisture. The same substance, according to him, cements the cell-walls.

Epidermal Appendages.—These consist of openings to which the name of stomates is given, as well as of hairs, glands, and scales. They are not invariably present in the epidermis of all plants, and some of them, after having been developed, disappear in the progress of plant growth. Their presence and absence, as well as their form and structure, give rise to important botanical characters. A surface without hairs is called glabrous, while one having hairs is pilose. When the hairs are short and soft, the surface is pubescent; when long, distinct, and tolerably soft, hispidae; when long and stiff, hispid; when the hairs arise in tufts, the term bearded or stipitate is applied. When they are entangled like cotton, and at the same time rather rigid, the term tomentose is given.

Stomata or Stomates.—These are orifices between the epidermal cells situated on the leaves and other green parts of plants exposed to the air, and communicating with intercellular spaces. They are sometimes called breathing-pores. power of opening or closing the orifice. When moist, these cells become swollen, and, while they lengthen, curve outwards in the middle, so as to leave a free opening; when dry, they are shortened and straightened, and thus their sides are applied to each other, so as to close the orifice. They are not found in underground roots, nor in plants which have grown excluded from light; and they are rarely seen in those which are constantly under water. They are best seen on the under surface of leaves. When the epidermis becomes hard and glazed, stomata sometimes disappear, or are altered in their appearance. Their form is usually oval or elliptical, but in some instances they are spherical or quadrangular. They are either scattered singly at regular or irregular intervals over the epidermis, or they are arranged in clusters. Their number varies from 200 to 160,000 or more in a square inch of surface. In the leaves of the White Lily there are 60,000 in a square inch on the under surface, and about 3000 on the upper; on the leaves of the Cherry-Laurel there are 90,000 on the lower surface, and none on the upper.

Hairs—are prolongations of the epidermal cells. They consist either of single cells, more or less elongated (Fig. 46), or of several cells placed in a linear series, like beads, as in Figure 47, or united both longitudinally and laterally, as in Figure 48, where the lower part of the hair consists of numerous cells. In Figure 49, the hair divides at the apex into two, in a forked manner. In Figure 50, a, it splits into cells which secrete an irritating fluid. The scales produced on the leaves of Oleaster (Fig. 53), and of some Begonias, the scurf on those of Bromelias, and the chaff (ramentum) covering the fronds of Ferns, are all modifications of epidermal cellular tissue.

Glands—are epidermal cells containing various fluid and solid secretions. They are either applied closely to the surface (sessile), as in the Ice-plant, where they appear as elevations of the epidermis, containing a transparent fluid like ice, or in the Hop (Fig. 54), where they appear as resinous scales of different shapes; or they are raised on stalks (stipitate) of different lengths, and then may be called glandular hairs, as in the Sundew. The bases of undeveloped hairs sometimes assume the appearance of glands. The secretions of glands are of an oily, waxy, resinous, gummy, saccharine, saline, acid, or irritant nature. The honey-like matter of the flower is secreted by glands. In Figure 55 is represented one of the leaves of the flower of the Crown-imperial, showing the depression, g, at its base, in which the honey is secreted; a similar pit is seen in the common Buttercup. The cells at the base of the Nettle hair (Fig. 48) contain an irritant secretion, those at the apex of the Sundew hairs contain viscid matter. The glands on the flower-stalk of Dittany and Rose secrete oil, while those of the Chick-pea have an acid fluid in their interior. On the inner surface of the base of the stipules of Cinchona and allied genera, there are numerous small sessile glands which secrete a gummy matter.

CHAPTER II.

NUTRITIVE ORGANS OF PLANTS.

Having now considered the Elementary Tissues of plants, their composition, and contents, we proceed to view them in combination, as forming various compound organs. These are naturally divided into the organs destined for the nourishment or Nutrition of the plant, and those concerned in Reproduction, or in the formation of the new plant. Viewed as individual beings, plants present various aspects. Some, like the Red-snow plant (Fig. 56), are composed of single isolated cells, which are capable of performing the functions both of nutrition and reproduction. Others, as Fungi and sea-weeds, are composed of cells united either in a linear series or as a flattened expansion, some of which are appropriated to the nutritive, and others to the reproductive functions. These plants are denominated Cellular. The higher classes of plants have cells and vessels... combined, presenting more complicated organs of nutrition and reproduction, and they are denominated Vascular.

In the lower classes of plants there are no evident flowers—their organs of reproduction are obscure, and hence they are called Flowerless and Cryptogamic; while the higher classes have conspicuous flowers, and evident organs of reproduction, and hence are called Flowering and Phanerogamous or Phanerogamous. In both classes the young plant, or embryo, in its earliest state, is cellular. This state is retained by the embryo or spore (Fig. 57) of the former; while in the latter it assumes a high degree of development in the seed, and at maturity exhibits the parts which are to form the root, stem, and leaves, associated with certain temporary leafy appendages or lobes, called cotyledons (Fig. 57).

When the spore of Cryptogamic plants is sown in the soil, it gives off root-like processes (Fig. 58), and either sends upwards a conspicuous stem with leaves, or produces a peculiar flattened expansion, called a Frond or Thallus, bearing organs destined for forming spores. There is no cotyledon or seed-leaf; hence the plants are called Acotyledonous (α, priv., and κότυλος, a seed-lobe). In Phanerogamous plants, on the other hand, when the seed is planted, the young root of the embryo, proceeding from one end of the primary axis, descends, while the stem ascends, bearing leaves and conspicuous flowers. This process is represented in Figure 59, where \( r \) is the young root coming off from the radicular end of the axis; and \( c \) is the stalk supporting the two cotyledons or seed-leaves \( c \), whence the plant is called Dicotyledonous (δι-, twice); \( g \) are the first leaves of the plant. The same process is seen in Figure 60, where the roots are seen proceeding from the lower part of the axis \( t \); the young stem is marked \( g \), and a single cotyledon or seed-leaf is seen at \( e \); whence the plant is called Monocotyledonous (μόνος, one).

When we take a comprehensive view of the Vegetable Kingdom, we find that all the organs of plants are formed upon one harmonious plan. All are produced from cells, which are modified and aggregated in various ways, and are fitted for the special functions performed by the different parts of plants. The organs called Root, Stem, and Leaves, with their modifications, are those destined for nutrition or vegetation; while certain cellular bodies in Cryptogamic plants, and the Flowers in Phanerogamous plants, are the organs of reproduction.

I.—ANATOMY OF THE NUTRITIVE ORGANS.

1.—THE ROOT OR THE DESCENDING PORTION OF THE AXIS.

The root (Fig. 59, \( r \)), generally speaking, is that part of the plant which descends into the soil, avoiding the light. It is the first organ developed from the axis of the embryo. The portion of the axis from which it arises is called radicular. In Figure 61, the embryo of a Pea exhibits, at \( r \), the portion of the axis from which the young root proceeds. This portion is called the Radicle; while the part \( t \) is connected with the ascending axis bearing the cotyledons (seed-lobes), \( e \), and the young stalk, \( g \), which lies in a depression, \( f \), of the cotyledons. The root consists at first entirely of cellular tissue; and, in cellular plants, this continues to be the case throughout life. In vascular plants it is strengthened by the addition of woody fibres and vessels, and presents the same internal structure as is seen in the stem. It may be considered a downward prolongation of the stem.

The extremities of the roots are composed of loose cells, which appear to be the terminal tissue of the radicle, carried forward by the elongating root. These cells have been called Spongiotes or Spongylets, but they ought not to be reckoned special organs. They do not consist of the newly-formed tissues, but they are in reality an annual mass of older cells, pushed forward by the root as it is developed, and when they decay, they are replaced by the layer beneath. Thus, according to Schleiden, the point of the root consists of older and denser tissue than that immediately behind it. In the structure of the root we rarely meet with true spirals. The epidermal covering does not present stomata; but hairs, usually formed of a single elongated cell, are produced, often in great abundance, which appear to serve the purpose of absorption. Figure 62 represents the magnified extremity of a young root of Orchis; \( c \) being the cellular tissue, passing into fusiform dotted cells and vessels, \( f \); \( p \) the cellular extremity of the root, called the spongiote, being marked \( s \); \( p \). The extremities of some roots, as those of Duckweed and Pistia, are covered by a little cap-like process, or Pilearhiza, (πίλος, a cap, and ῥίζα, a root), which consists of a cellular layer, separating from the external parenchyma, but still retaining its connection with the point of the root, which perishes if the covering is removed.

The young roots of Cryptogamic or Acotyledonous plants arise from every part of the surface of the cellular axis or spore (Fig. 58), and hence the plants have been called by Richard Heterorhizal (ἕτερος, diverse, and ῥίζα, root). In Monocotyledonous plants, the young roots arising from the ra- Botany. dicular portion of the axis separate into numerous fibres (Fig. 63, r), which, in piercing the axis, are covered with a

are sometimes covered, as in the Screw-pine, with a peculiar cap-like covering. These abnormal roots ultimately reach the soil, and become subterranean, serving to support and prop up the trees to which they are attached.

The aerial roots of Iriartea are covered with numerous spines. In Epiphytes, or plants growing in the air, attached to the trunks of trees, such as Orchids, the aerial roots produced do not reach the soil. They continue always aerial and greenish, and they possess stomata. Delicate hairs are often seen on these Epiphytal roots, as well as a peculiar investment over their true epidermis. The aerial roots of the Ivy are not the proper roots of the plants, but simply processes intended for mechanical support.

Parasitic plants, as the Mistletoe, Boom-rape and Rafflesia, send root-like processes into the substance of the plant whence they derive nourishment. In the Dodder,* the bark *Pl. CXXV over the roots swells into a kind of sucker (haustorium), which is applied flat upon the other plant, and ultimately becomes concave, so as to attach the plant by a vacuum. From the bottom of the sucker the root protrudes which penetrates the supporting body. In the case of parasitic Fungi, such as mould, there are cellular filaments which spread among the tissues of plants, and which may be looked upon as equivalent to roots and stems united. They form the spawn or mycelium of these plants, and in some cases cause rapid destruction of the tissues of plants, as in the disease called Dry-rot.

Roots vary in their duration. In plants which grow up, flower, and die in one year, they are annual. In such cases they are usually composed of slender fibrils, which are deciduous, like leaves. These roots, consisting of numerous fibrils, springing from one point, are called Fibrous (Fig. 68). They are seen in many annual grasses.

Plants which spring from seed one year, and flower the second season, and then die, have biennial roots; while those which continue to live and flower for many years, have perennial roots. In the last two cases the roots are often of a fleshy or woody consistence.

Perennial woody roots, when cut transversely, exhibit a structure similar to that seen in stems. Fleshy roots contain much starch, sugar, and gelatinous matter in their structure. They either descend singly, in an elongated tapering form, without branching, giving rise to various forms of Top-root—conical in the carrot, fusiform or spindle-shaped in the radish, and napiform in the turnip; or they branch off in a fibrous-like manner, giving rise to Fasciculated* roots, as in Ranunculus and Dahlia, and Tuberculate or Tu-

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*Fig. 65. Grain of Oats, a Monocotyledon, sprouting. The roots, r, passing through the soil, give rise to adventitious roots, c, and the young stalk and leaves, p. Richard calls it Endorhiza.

*Fig. 64. Seed of Orange, a Dicotyledon, sprouting, showing the root, r, descending and tapering, c, the cotyledons in the seed, t, the young leaf, p. The plant is called Exorhiza by Richard.

*Fig. 66. Pandanus odoratissimus, the Screw-pine, giving off numerous aerial roots near the base of its stem.

*Fig. 67. Rhizophora Mangrove, the Mangrove tree, supported as it were, upon piles by its numerous roots, which raise up the stem.

*Fig. 68. Fibrous root of a grass. Numerous fibrils springing off from one point. Botany.

In Ipecacuan there is a peculiar Annulated root, showing contractions at short intervals, while in Spiraea Filipendula the root becomes Nodose, presenting irregular swellings on its fibrils. Occasionally a Tap-root is suddenly arrested in its growth, and in place of tapering to a point, ends abruptly. This is seen in the Bitten-rooted Scabious, the root of which is called Premorse. In some cultivated plants, as turnip, the central root is sometimes injured, so as to end abruptly, and it then divides into numerous branches, resembling a fasciculated root. This gives rise to the disease called Fingers and Toes, which is very injurious to the crop. The mode in which the fibres of roots are produced and developed, thus gives origin to different forms of Rhizotaxis (pifa, root, and raçé, order), or root-arrangement.

II.—THE STEM OR THE ASCENDING PORTION OF THE AXIS.

1. Various Forms of Stems and Branches.

The stem is the ascending portion of the axis which is developed in an opposite direction from the root. It differs from the latter in usually seeking light and air, in bearing leaf-buds, which are produced at regular intervals, and in growing throughout its whole extent. In flowering plants conspicuous stems are met with, which differ in their texture, some being herbaceous, and dying down annually to the ground, others being woody and permanent, as in trees and shrubs. When stems are weak and trail on the ground, they are called prostrate or procumbent, when such stems rise towards their extremity they are decumbent, and when they rise obliquely from near the base they are ascending. Some stems are so slender that they require the aid of other plants for their support. They are either climbing and scandent plants, such as the Passion-flower, which clings to other plants by tendrils, or the Ivy, which adheres to rocks and walls by its root-like processes; or they are twining, when the whole stem coils round other plants in a spiral manner, the coils being either from right to left, i.e., to a person supposed to be in the centre of the coil, and the stem twining across his chest from his right to his left, as in Convolvulus, Phaseolus vulgaris, and Dodder; or from left to right, as in the Hop and Tamus.

Names are given to plants according to the nature and duration of their stems. Herbs, or herbaceous plants, have stems which die down annually. In some of them the whole plant perishes after flowering; in others, the lower part of the stem forming the crown of the root remains, bearing buds, from which the stem arises next season. In what are called biennial herbs, the whole plant perishes after two years, while in perennial herbs the crown is capable of producing stems for many years, or new annual products are repeatedly added many times, if not indefinitely, to the old stems. The short permanent stem of herbaceous plants is covered partially or completely by the soil, so as to protect the buds.

Plants producing permanent woody stems are called Trees and Shrubs. The latter are less than five times the height of a man, and produce branches from or near the ground; while the former have conspicuous trunks, which attain at least five times the height of a man. Shrubby plants of small stature are called Under-shrubs or Bushes. The limits between these different kinds of stem are not always well defined; and there are some plants occupying an intermediate position between shrubs and trees, to which the name of arborecent shrubs is occasionally given. The usual name given to the herbaceous stem is Caulis; in grasses the stalk is called a Culm; while in Palms and Tree-Ferns the stem is denominated Caulex and Stipe.

Stems sometimes assume anomalous forms. In the Tortoise-plant, or Elephant's-foot-plant, the stem forms a large irregular thick mass, with a rough and tuberculated exterior. In the Melon-Cactus it is globular, in other species of Cactus, it is jointed, columnar, or angular; while in many Orchids (Fig. 70) it assumes an oval or rounded form, and is called a Pseudo-bulb. The stem is so short in some plants, as the Primrose, Cowslip, Gentian, and Dandelion, that they are called Stemless or Acadulescent. A similar term is given in ordinary language to plants whose stems are buried in the soil, such as Cyclamen or Sow-bread.

The stem, although it has a tendency to rise upwards when first developed, in many instances becomes prostrate, and either lies along the ground, partially covered by the soil, or runs completely underneath its surface, giving off roots from one side, and buds from the other. Some stems are therefore subterranean, and are distinguished from roots by the provision made for regular leaf-buds.

The points where leaves or leaf-buds are produced are called Nodes. In certain jointed stems or branches, as the Bamboo, these are well marked; but in stems which are not articulated, the nodes are often distinguished chiefly by the leaves which they bear, or by the scars left after their fall. The intervals between the nodes are denominated Internodes, and they are of different lengths, according to the distance at which the leaves are placed from each other.

The stem may be considered as formed of a series of leaves, at first closely aggregated on a shortened axis, and afterwards separated by more or less evident intervals. As the leaves decay and fall off, the stem becomes more conspicuous and uninterrupted. Buds may be regarded as shortened leaf-bearing axes, capable of elongation, so as to form stems and branches, with nodes and internodes. Some buds are terminal, or are produced at the extremity of the primary axis, just as the first bud in the Embryo-plant. These buds in their after-growth continue to add to the length of the stem. Other buds are lateral, or are produced on the sides of the axis. These are concerned in the production of branches.

In trees which do not ramify, as most palms, there are no lateral buds. In plants which have permanent stems, and in which the leaves are deciduous, provision is made for subsequent growth, by the production of buds which lie dormant during the winter, or the season of repose, and are ready to burst forth when the spring or the rainy season returns. The buds are situated at the angles where the leaves join the stem, or in what is called the Axis of the leaves. In cold and temperate climates these buds are protected by a coarse external scaly covering, and sometimes also by a waxy, glutinous, or resinous matter, as is well seen in the Horse-chestnut.

Buds, in place of producing branches, are in some instances abortive, or remain latent, ready to be developed when any injury has been inflicted on the terminal buds or branches. Occasionally, after a partial development as branches, buds are arrested and form knots or nodules. The embryo-buds or nodules of the Beech, Cedar, and Olive, are apparently of this nature. Sometimes several Buds unite together in the axil of a leaf, and form a peculiar flattened branch.

Branches are sometimes long and slender, and run along the ground, producing roots and leaves at their extremity or apex. This is seen in the Runner (flagellum) of the Strawberry. In the Houseleek (Sempervivum) there is a similar prostrate branch of a shorter and thicker nature, producing a bud at its extremity capable of independent existence. It receives the name of Offset (propagulum). A Stolon differs from these in being a branch which curves towards the ground, and, when reaching a moist spot, takes root and forms an upright stem, and ultimately a separate plant. It is a sort of natural layering, and the plant producing such branches is called Stoloniferous.

Spines or Thorn are usually abortive branches ending in sharp points. This is shown by their producing leaves occasionally (Fig. 71), and by their being frequently changed into ordinary branches during cultivation. Plants bearing thorns (modifications of branches or leaves) are denominated spiny, spinose, or spinescens. Tendrils (cirri) are frequently an altered state of leaf-buds or branches, as in the Passion-flower and the Vine, enabling the plants to climb. In the Vine, as represented in (Fig. 72), the tendrils, v e r, are considered by some as the terminations of separate axes. The lowest leaf in the figure is connected with the first axis, which ends in a spiral tendril, v; and between this tendril and the leaf a bud is given off, forming a second axis, which ends in the second tendril, v; between which and this second axis another bud is given off, forming a third axis, ending in a third tendril, v, and so on. The different axes are in this case called cirri.

Subterranean Stems and Branches are sometimes short and thick, at other times they are elongated. Some are completely under ground, while others are only partially so; some increase by lateral, others by terminal buds. Many of them are in the ordinary language called roots, from which, however, they are distinguished by the power of forming regular buds, or by having rudimentary leaves or scales on their surface. Many of them contain much nourishing matter, which is stored up for the future growth of the plant.

Rhizome, or root-stock, is the name given to certain root-like forms of creeping stems, which are more or less completely subterranean. They are seen in Iris, in Ginger, Botany, and Convallaria (Fig. 73). Such stems exhibit on their upper surface the marks or scars of leaves, and it is to the scale-like appearance of these markings that the plant called Solomon's seal (Fig. 73) owes its name. Of a similar nature is the Scolotes, or creeping stem of Carices, Papyrus, and other grass-like plants, which spread through the sand and loose mud in such a way as to bind the particles together.

In the Banana (Fig. 86), there is an underground stem which sends up shoots of a herbaceous nature to bear the flowers and the fruit. In Asparagus the shoot developed from the subterranean stem is called a Tuber; it is the part used as an article of diet; at first it is covered with scales, but it afterwards gives off branches, which bear leaves, flowers, and fruit. In the Rose and Mint a subterranean branch arises from the stem, which runs horizontally to a certain extent, and ultimately sends up an aerial stem, which becomes an independent plant. Such branches are denominated Suckers, and the plants are called Suckulose. The gardener divides the connection between the sucker and the parent stem, in order to propagate these plants.

The Tuber is a subterranean branch, which is arrested in its growth, and becomes remarkably thickened, in place of being elongated. It is seen in the Potato and Jerusalem Artichoke; and the eyes produced in these instances are true leaf buds. When the older parts die away, these tubers are found to belong to one axis with the new structures, which are subsequently formed. In the Arum, Colchicum, and Crocus, the tubers are perfected after the other parts, which belong to the same axis with themselves, so that they and the new structures belong to two axes, or at least to two different processes or shoots of the same axis. Such tubers are called Corms. They have a central axis, which is sometimes covered by thin scales; and they may be looked upon as shortened axes with scaly leaves, or as subterranean buds. Corms may be regarded as dilated stems intervening between the first buds and the roots. They give off buds in the form of young corms, and occur in monocotyledonous plants. In Gladiolus, the new corms are so superimposed upon each other, that they gradually rise above ground. In Colchicum (Fig. 74) the new corm, b, is produced alternately at either side of the old one, a, which shrivels. Sometimes three generations may be seen at the same time—the old corm, the new corm, and the bud of next year.

The Bulb is also a short subterranean axis, which is covered with fleshy scales containing succulent cells. It is a bud produced under ground, the centre corresponding to the axis, which is clothed with scales, and which sends flowering stems upwards, and roots downwards. In the Lily the thick and narrow scales are arranged separately in rows, and the bulb is called scaly; while in the Leek, the scales are broad, and inclose each other in a concentric manner, the outer ones being thin and membranous, and the bulb is said to be *tunicated*. The scales are equivalent to leaves, and they produce buds in the form of cloves or young bulbs at the part where they join the axis. At the base of the bulbs there is a flattened rounded portion, which produces roots from one side, and scales and leaves from the other.

The central bud produces the flowering stem. The lateral buds or cloves sometimes remain attached to the axis, and produce flowering stems, so that the same bulb continues to flower for many years, as in the Hyacinth and Tulip; at other times the young bulbs are detached, and form separate plants. In the case of some plants, as Lilium bulbiferum (Fig. 75); bulbs are also produced on the stem, in the form of bulbils or bulblets, b, which are scaly buds, capable of being detached, and of forming independent plants.

2. Internal Structure of the Stem.

The forms of the stem having been considered, we now proceed to examine its anatomical structure. This structure consists of the elementary tissues combined and arranged in various ways. In some plants the part which serves the purpose of a stem is composed entirely of cells arranged in the form of very narrow filaments, which are simple or branched, as in some Fungi* and Coniferous, or which form an expanded surface, called a Thallus or frond. Such cellular plants have received the name of *Thallopses* or *Thallophytes* (*θάλλος*, a frond); while those producing stems composed both of vessels and cells are sometimes called *Cormogens* or *Cormophytes* (*κορμός*, a stem or stipe). In ordinary conspicuous stems, both cellular and vascular tissue are present.

The arrangement and development of the cellular and vascular systems give rise to three marked forms of stems:

1. *Acrogens*, in which the bundles of vessels are simultaneously developed, and the additions to the stem take place at the summit, by the union of the bases of the leaves. Plants having this kind of stem are called *Acrogens* (*ἀκρός*, summit, and *γεννᾶν*, to produce), or Summit-growers. Tree-ferns furnish an example.

2. *Endogenous* (*ἔνδον*, inwards), in which the bundles of vessels are definite, and are deposited towards the centre, which becomes filled up with them in the progress of growth, so that the diameter of the stem increases in a great measure by the new matter pushing out that previously formed. Such plants are called *Endogens*, or Inside-growers. Palms and Screw-pines supply examples.

3. *Exogenous* (*ἐξωτερικός*, outwards), in which the bundles of vessels are produced indefinitely in an outward direction, and the stem increases in diameter by the annual formation of a new layer of woody matter formed on the outside of the preceding layers. Such plants are called *Exogens*, or Outside-growers. Ordinary trees, such as the Oak and Ash, furnish instances.

While the structure of the stem supplies obvious characters, it will be found that other distinguishing marks separate these three great classes of plants even in their earliest state. Thus, Acrogens are *Acotyledonous* (Fig. 58); Endogens are *Monocotyledonous* (Fig. 60); and Exogens are *Dicotyledonous* (Fig. 59).

a. Exogenous Stem or the Stem of Dicotyledonous Plants.

Exogens are the largest class of plants in all parts of the globe, and the structure of their stems is familiar to us in the trees of cold and temperate climates. In Britain the trees of our forests are all exogenous in their formation. Such trees, however, occur also in warm regions, associated with others exhibiting endogenous and acrogenous structures.

An exogenous stem, in its earliest condition, is entirely cellular. When the plant begins to grow and send up its first leaves, the cellular tissue of the axis is seen to be traversed by bundles of vessels (vascular bundles), which soon divide the stem into two marked portions; an internal, forming the central pith or medulla, and an external, forming the cortical pith or bark, covered by epidermis. The connection between the central pith and cellular bark is kept up by means of lines of cellular tissue, called medullary rays, which are interposed between the vascular bundles. At the end of a year's growth, we observe, in the exogenous stem, a central cellular pith, a circle of vascular bundles in the form of wedge-shaped masses, an external bark and integument, and rays passing from the pith to the bark. This is the complete structure of exogenous herbaceous stems, which die down annually. The appearance is exhibited in Figure 76, which is the young stem of a melon cut horizontally; m is the medulla or pith, composed of loose cells containing fluid; t, tracheae or spiral vessels immediately surrounding it, and forming a medullary sheath; r m, medullary rays, composed of more or less flattened cells, which extend from the pith to the external cellular bark or cortical layers; on the outside of the bark is the integument with projecting hairs, and between the medullary rays are ten wedges of fibro-vascular bundles, consisting of woody, porous, annular, reticulated, and spiral vessels; in these wedges the porous vessels are represented by large rounded openings. In Figure 77 is given a horizontal section of one of the fibro-vascular bundles, in order to show its composition. The section extends from the pith to the outer integument; m, medulla or pith; t, tracheae or spiral vessels, forming the sheath round the pith, the fibres being unrollable; r m, cellular medullary ray at the side of the vascular wedge; f, woody, annular, and reticulated vessels; v p, porous or pitted vessels of large calibre; c, a layer of green and active cells, forming what is called the cambium layer; l, woody fibres, constituting a layer called the inner bark; e l, ramifying lactiferous vessels; p c, cortical cells, constituting the cellular bark, which is covered by the common integument, e.

In stems which are not annual, the growth of the second year consists of a new formation of vascular bundles outside the previously formed layer, between it and the bark—the connection between the pith and the bark being still kept up by cellular rays. Between the pith and the bark there are annually formed a layer of active formative cells, called cambium cells, which are concerned in the development of new woody fibres. In Figure 78 is shown a transverse section, A, and a vertical section, B, of one of the fibro-vascular bundles of the maple at the commencement of the second year of growth—the letters referring to both sections; \( t \), tracheae, or spiral vessels, forming the medullary sheath, which allows the medullary rays to pass through at different points; \( p \), porous or pitted vessels, constituting bothrenchyma or taprenchyma, and presenting large rounded openings; \( f \), fibres formed of fusiform tubes, the inner, \( f \), marking the fibres forming the wood of the stem, and the outer, \( f \), those which form the cortical fibres of the inner bark; \( c \), cambium cells between the wood and bark; \( p \), \( p \), cortical polyhedral cells, often of a greenish colour, forming a cellular layer of bark; \( s \), outer cellular layer of bark, composed of cubical or tabular colourless cells, often of a corky nature, and hence called suberous; this cortical layer is covered by the general integument. Thus, at the commencement of the second year's growth there is a distinct formation of cambium cells, by the action of which a new layer of wood, and a new layer of fibrous bark is formed; and these cambium cells, being in connection with the medullary rays, keep up the connection between the medullary and cortical cells.

Let us now trace the changes which take place in the permanent woody stem of the Maple, after three years' growth, as represented in Figure 79. The yearly growth of the woody bundles is marked by the Figures 1, 2, 3—1. The Pith, \( m \), is surrounded by tracheae, \( t \), which are not repeated in the growth of subsequent years; outside these are the pitted vessels, \( v \), and fibrous tissue, \( f \), of the first year's growth. 2. Pitted vessels, \( v \), and fibres, \( f \), or woody and other vessels of the second year's growth. 3. Pitted vessels, \( v \), along with fibres, \( f \), of third year; \( e \), layer of cambium cells outside the wood of third year. The outer part of the section consists of the layers of bark; \( s \), the suberous, or outer layer of bark cells; immediately within, is \( p \), the cellular layer, and \( l \), the fibrous layer of the bark of the first year; then follows the bark of the second year, \( p \), and, finally, the cortical layers of the third year, \( p \), which are separated from the wood by a cortical layer of new cells, \( m \), and the cambium layer, \( c \).

In examining, therefore, the growth of an Exogenous stem, it will be seen, that while additions are yearly made to the layers of wood in an outward direction, so as to give rise to the term Exogen, or outside-grower, the bark, on the contrary, increases by annual additions on the inside. The increase of the diameter of such stems takes place by successive deposits of vascular wedges in concentric circles, year after year, and during this growth the bark becomes gradually distended. On examining old stems the different annual layers can be counted, especially in trees of cold and temperate climates, where there is a marked cessation of growth during winter.

Let us now proceed to examine the different parts of an Exogenous stem proceeding from the centre to the circumference.

The Pith (Fig. 76, \( m \))—consists of cellular tissue (parenchyma), at first succulent, but afterwards becoming dry, as its juices are absorbed for the use of the young plant. The dry pith of the stem is sometimes used for paper, as in the case of Rice paper or Schola, which is produced in India from the stem of Aschynomene paludosa, in the Malay Archipelago from that of Scavola Taccada, and in China from that of Aralia papyrifera (Tung-tsaou). In the progress of growth its cells are sometimes broken up, so as to form large empty cavities, as in the Walnut, Pole, Jessamine, Horse-chestnut, and Hickory; at other times the whole pith gives way, owing to the rapid distension of the outer part of the axis in its early state, and then the stem becomes hollow, with shreds of pith attached to its interior, as in Umbelliferae* and Grasses. The cells of pith are well seen under the microscope in the Elder.

The Medullary Sheath—is the first formed vascular layer (Fig. 77, \( t \)). It consists principally of spiral vessels (Fig. 30), the fibres of which can be uncoiled. This is the only part of an exogenous stem in which these vessels ordinarily occur. This medullary circle is not always complete, spaces being left between the vessels where the medullary rays and the pith communicate. The tracheae traverse the cellular tissue so as to reach the leaves.

The Wood.—The layers of wood (Fig. 77, \( f \)) are formed outside the medullary sheath. They consist of woody fibres (prosenchymatous tubes) such as those represented in Figure 24, mixed with dotted ducts (Fig. 3), and occasionally with a few annular (Fig. 32) and reticulated (Fig. 33) vessels belonging to the spiral type. On making a transverse section of the stem of the Chestnut, Ash, or Oak, the extremities of the dotted ducts (pitted vessels) will be seen in the form of large rounded openings on the inner side of the woody circle or zone. In the Maple (Fig. 79), Plane, Lime, and Hornbeam, the openings are large, and are diffused throughout the annual zones, mixed with pleureenchyma. In coniferous (cone-bearing) plants, as the Fir and Pine, the woody layers are composed of disc-bearing pleureenchyma (Fig. 25), without any dotted ducts, and hence under the microscope no large rounded openings are seen in the woody layers.

In the young state the pleureenchymatous tubes of the woody zones are pervious, but by degrees they are obliterated by the deposits of ligneous matter (lignin). In old exogenous trees the central wood is hard and durable, constituting the Heart-wood or Duramen, while the exterior wood is soft, forming the Sap-wood or Albarnum. The lignin deposited in the heart-wood frequently acquires a marked colour, as in the Ebony tree, where it is black; in the Black Walnut, where it is dark-brown; in the Barberry and Judas-tree, where it is yellow; in the Red Cedar, where it is purplish-red; and in the Guaiac tree, where it is greenish. The relative proportion between albumen and duramen varies in different trees. Those in which the hard wood predominates are best fitted for building, and for withstand- ing the effects of moisture, dry rot, and the attacks of insects and other animals. The durability of woods depends on the nature of the ligneous matter deposited in their phe- renchyma, and this varies much.

The woody zones annually formed are not always of the same size. Much depends on the state of the climate and season, the exposure of the plant to air and light, and the nourishment which it receives. A narrow ring of wood may be considered as recording a cold season, while a wide one indicates a warm season. The same zone also varies in size at different parts, so that, in many cases, the pith is excentric—that is, not exactly in the centre of the stem, owing to the circles being thicker on one side than on the other. Bravais and Martins noticed a Scotch Fir in which the two semi-diameters of the stem were to each other as nine to nineteen, or the one more than double the other. In such cases, it usually happens, that the side of the tree having the greatest thickness is that which has been best exposed to air and light.

From the mode in which layer after layer of wood is formed, it follows that the age of an exogenous tree may be estimated by counting the number of woody circles (Fig. 80.) In trees of cool climates, where there is a marked cessation of growth, this may be done with tolerable accuracy up to a certain age at least; but in trees of warm climates, where there is a less marked period of repose, this cannot always be done accurately. It is said that in some of the trees of tropical America monthly circles are formed; while in species of Cactus and Cycas more than one year is required to form a single zone. In estimating the age of trees in temperate climates, the rings or zones of woody matter must be counted from the pith to the bark. Mistakes have been committed, in many instances, by merely making a section of a stem, embracing a few zones, and then estimating from their size for the whole diameter of the tree.

The Medullary Rays.—These connect the pith and the bark (Fig. 76, r, m). They consist of flattened quadrangular cellular tissue, having an appearance like bricks in a wall, and hence called muriform. In the young stem these rays are large, while in the more advanced woody stem they are seen as lines only. They constitute the silver-grain so conspicuous in the Maple, and they give the peculiar silvery lustre to many woods when cut in the direction from the pith to the bark. These rays do not proceed in a continuous plane from the top to the bottom of the tree. They pass through the woody layers in such a way as to be interrupted in their course, and when a section is made perpendicularly to the rays, or, in other words, as a tangent to the circumference of the stem, their ends are seen projecting irregularly through the woody fibres. They are said by some authors to represent the horizontal system of the stem, or, as it were, the wool, which is traversed by the vertical woody bundles, like the warp. The medullary rays are in some cases, as in Clematis and Aristolochia, large and broad, while the woody wedges are comparatively small. Besides complete medullary rays, there exist others which only extend partially through the stem.

The Cambium Layer.—This is a layer of nucleated cells, lying between the wood and the bark, and originally connected with both. They are formed in a mucilaginous fluid called Cambium, and they are concerned in the formation of the woody tubes of the inner bark, and of the phe- renchyma, as well as in the additions made to the cells of the medullary rays. When these cells are carrying on the process of growth with activity, during the flow of the sap in spring, the bark can be easily separated from the wood.

The Bark—is at first composed of uniform cellular tissue, resembling that of the central part of the stem (Fig. 77). In the progress of growth transformations of the tissue take place, by which fusiform procenchymatous tubes are formed in the inner portion of the bark next to the woody circle. This process is called the Inner Bark or Liber (Endophleure—interior, within, and phloos, bark). It consists of thickened pherenchyma with some laticiferous vessels. It is the fibrous part of the bark, and is often called Bast tissue. The fibres of the liber are long and tenacious, and are employed for various useful purposes. Those of the Lime-tree, Hemp, Mallow, Hibiscus, Boehmeria, Nettle, and Daphne cannabina, are employed for different articles of manufacture. The fibres sometimes separate, so as to form meshes, as in the Lace-bark tree. The inner bark of Antiaris saccidora has tenacious fibres, which are used in India for cordage and matting. The tree is common in the jungles near Coorg, according to Dalzell, and the people manufacture curious sacks from it. A branch is cut corresponding to the length and breadth of the sack wanted. It is soaked a little, and then beaten with clubs until the liber separates from the wood. The liber, in the form of a sack, is then turned inside out until the wood is sawed off, with the exception of a small piece left to form the bottom of the sack. These sacks are in general use among the villagers for carrying rice. The inner bark of various trees has been used for writing upon, and hence the name liber.

On the outside of the liber lies the cellular portion of the bark, consisting of two layers, the Cellular Envelope, called also Mesophleum (inter, middle), and the Corky or Sub- serous Envelope, called also Epiphleum (ext, upon, on the outside). The former is composed of loose thin-walled polyhedral cells, containing chlorophyll, and hence often denominated the green layer; the latter consists of flattened tabular parenchyma, giving the peculiar colour to the branches and young stems of trees and shrubs. The epiphleum is rarely green; it is generally some shade of ash-colour or brown. It is sometimes developed to a great extent, constituting the cellular substance called cork, procured from the Cork-oak, and produced also by various species of Elm. In some trees the epiphleum falls off at certain intervals. In the Cork-oak it does so in eight or nine years, leaving a tabular layer of cells below. In the Birch the outer bark is the part which separates in layers, owing to the formation of a stratum of thin-sided cells below the lamella, which easily separate into fine powder when disturbed. On the outer surface of the epiphleum is the Epidermis, or general integument, which in old trunks is thrown off.

The different layers of bark increase by additions of new cells to their inner surface. The cellular layers, however, soon cease to grow, while the liber continues to increase by additions from the cambium layer. The thickening of the pherenchyma of the liber takes place by concentric deposits of lignin, in the same way as in the case of woody tubes. Sometimes the different annual circles of bark may be traced, but in general, after a certain length of time, all the layers are more or less amalgamated by the growth and pressure of the parts below, so that it is impossible to ascertain the age of the tree by the cortical layers. It is obvious that, by the constant additions to the wood on its outside, and the bark on its inside, the latter is distended, and when the cellular portion has ceased to grow, it cracks and splits in various ways, and ultimately falls off. The distension and increase in diameter of an Exogenous stem is such, that a woody climbing plant, for example Bauhinia or Honeysuckle, when surrounding it, gives rise to marked grooves on the surface, and often arrests its growth entirely by pressure on the sap wood.

Although all these parts are generally observed in Exogenous stems, and present the order now mentioned, still, various peculiarities occur, especially among exogenous trees of warm climates, which often obscure the arrangement. Thus, in some trees of great age only one marked zone or circle of woody matter is seen, consisting of a series of separate wedges; in other trees there are several such zones, each of which is the produce of more than one year's growth. In such cases the stem increases in diameter by the formation of new wedges, or by additions to the old ones. Occasionally the woody matter is so formed as to be in separate masses, surrounded by cellular tissue, which presents the same appearance as the outer bark (Fig. 81). Such a stem looks as if it was formed by several united together.

Some Exogenous plants with twining stems become much altered by compression; other exogens exhibit fluted stems. In the Yarroua wood, or Paddle-wood (Aspidosperma excelsum), the stem is singularly fluted, and presents a waved or sinuous aspect. The same kind of appearance is seen in some woods which are imported for the purpose of furnishing dyes, such as Logwood, Nicaragua wood, and Rio de la Hache wood (Crasalpinia echinata), &c.

The Branches of Exogens.—In Exogenous stems a provision is usually made for the formation of branches, or, in other words, the stems grow, not merely by producing buds at the apex, which cause an increase in height, but also by lateral buds which give origin to branches. These are connected with the centre of the stem, and their tissues can be traced to the pith and its sheath. From this mode of growth Exogenous trees have a form more or less tapering as regards their stem and branches. In the arrangement of their parts, branches resemble the stems from which they proceed. When regularly developed they taper to a point, and continue to produce buds, which again form smaller branches and twigs by constant subdivision.

The mode in which branches grow and subdivide gives rise to different aspects in forest trees. In the Cedar, the branches spread nearly at right angles; in the Italian Poplar they come off at an acute angle with the upper part of the stem; in some plants, as the Weeping Elm, they come off at an obtuse angle. In the Birch and Willow the branches become so slender at their extremities that they bend by their own weight. When the terminal bud of a stem or branch of an Exogen is cut off or arrested in its growth, the lateral buds are produced abundantly, and thus give rise to the appearance seen in pollard trees, and in the clustering of the twigs of the Birch and other trees. The comparative length of the branches in the upper and lower parts of trees tends also to give them a peculiar physiognomy. When the lowermost are longest, and the others are gradually shorter as we proceed upwards, the conical form is produced, as seen in the Douglas Pine (Abies Douglasii). When the uppermost are longest, as in Pinus pinea, the form is somewhat like that of an inverted cone. When branches are produced under ground, and in darkness, they frequently become thickened and contorted in various ways, as seen in the potato, the tuber of which is a branch of this kind. When the potato is allowed to grow above ground, but in darkness, the ordinary branches sometimes assume the form of tubers.

b. Endogenous Stem, or the Stem of Monocotyledonous Plants.

This kind of stem is not seen in its fullest development in northern climates. We must look to the Palms and Screw-Pines of warm regions, in order to see the striking effect produced by its mode of growth. The trunks of palms differ much in their aspect from the trees of this country. They have usually simple unbranched, cylindrical stems, towering to a great height, and covered by a large mass of remarkable foliage (Fig. 82).

In the structure of the woody endogenous stem there is no marked distinction between pith, wood, and bark; there are no medullary rays, nor concentric circles. Definite vascular bundles are diffused through the cellular tissue without apparent regularity, and the whole is enclosed by an external covering which differs from the bark of Exogens, in not having annual layers, and in not being separable from the wood. In Figure 83, which exhibits a transverse section of a Palm-stem, this arrangement of tissues is seen. On the outside is the cortical portion not separable from the rest; the vascular bundles are marked f, and the cellular portion, which is looser towards the centre, m. In the early state the stem is entirely cellular, but in the progress of growth vascular bundles are produced, consisting of woody, spiral, dotted, and laticiferous vessels. In Figure 84, there is represented a transverse section of one of the fibro-vascular bundles of an Endogenous stem; upper p marking the general cellular parenchyma surrounding the bundle; lower p, woody fibres; I I, woody vessels analogous to those of the liber; t, tracheae (spiral vessels); v, dotted vessels of large calibre; v I, laticiferous vessels. The vascular bundles are most abundant near the circumference, while the cellular tissue is in larger quantity in the centre. In the bundles the woody vessels (Fig. 84, I I), generally surround the other vessels.

The vascular bundles may be traced from the leaves downwards, some proceeding more or less directly towards the root, others curving outwards towards the cortical integument or rind (Fig. 85, f e). The mode in which these bundles proceed from the leaves towards the centre, in the first instance, has given rise to the term Endogenous, or inside-growers; the idea originally entertained by physiologists being, that the vascular bundles were always produced on the inside of those which preceded them. The bundles, however, although they have a tendency towards the centre at first, do not always remain there, but follow a curved course towards the periphery, and in this way the outer rind becomes completely incorporated with them, so as not to be separable. The structure of the bundles varies in different parts of their course. Near the base of the leaves they contain all the vessels already mentioned, but as we trace them downwards, the spiral, dotted, and laticiferous vessels disappear, and the woody fibres alone remain when they reach the rind, or, as it is often termed, the false bark.

From the mode in which the vascular bundles are added, it will be seen, that the tendency is to push the older vessels outwards, and to render the periphery hard. In Palms, therefore, the hardest part of the stem is external, which is the reverse of what takes place in Exogens. By the internal addition of vascular bundles from terminal buds only, and by the interstitial growth of cells, the stem of a Palm increases in diameter until it acquires the full limit to which the outer rind can be distended, and attains ultimately a uniform diameter throughout. Thus, there appears to be a definite limit to the lateral growth of a Palm, while no such limit can be seen in the case of Exogens, in which vascular bundles go on increasing indefinitely, and the bark is separable. Palms consequently do not exhibit trunks of a diameter equal to that of Exogenous trees, nor does their bole present a tapering form. The first part of the stem of a Palm is formed by vessels which are connected with the first crown of leaves; the next crown, or terminal bud, produces more woody bundles internal to the first, and thus the stem is thickened during successive seasons, until at length the lower part is fully formed. The same process goes on throughout the whole stem, until it acquires a continuous cylindrical form. From the structure and mode of growth of a Palm-stem, it follows, that a woody twining plant does not produce the same injury as in the case of an Exogen.

Palms grow in a uniform manner as regards height in their native countries, and their age may in general be determined by the length of their stem. The destruction of the terminal bud of the Palm stops its growth, in consequence of the want of provision for lateral buds. In some instances, however, as is particularly seen in the Doum Palm of Egypt (Hyphaene thecaica), branches are given off in a forked, or what is called a dichotomous manner. There are also many endogenous stems which produce lateral buds. The Screw-Pine (Pandanus), for instance, and species of Dracena, have branching stems. In the Dragon trees (Dracena), a remarkable increase of stem takes place in consequence of the cortical integument remaining soft, and capable of unlimited distension. The vascular bundles, after reaching the circumference in these plants, descend towards the root, and being produced both by terminal and lateral buds, they are developed in large quantity, and thus give rise to enormous stems. Such a stem is seen in the famous Dragon tree of the Canaries, which near the ground is 70 feet in circumference. When numerous buds are produced laterally, the lower part of the stem receives more bundles than the upper, and thus the stem tapers. This is seen in the Asparagus Botany, and Bamboo, which in this respect resemble Exogens.

In some Endogenous stems the rapid growth of the outer part gives rise to a rupture of the central cells, and thus the hollow stems of many grasses are produced. In the Bamboo the hollow cavities in the stem are separated by partitions formed by the crossing of the vascular bundles. In Xanthorrhoea Hasilie, the grass-tree of New Holland, a liaceous plant, the structure of the stem and branches is peculiar. On making a vertical section the structure appears to be that of an Exogen. The woody part is formed of vertical loose fibres like Palms, and there are other fibres, radiating from the centre, and cutting the preceding at right angles. These horizontal fibres resemble the medullary rays, but differ in their structure. They probably serve for the origin of leaves, which are numerous, and are disposed throughout the whole length of the stem.

Endogenous stems sometimes remain under ground. The corn is in fact a shortened endogenous subterranean stem. Bulbs, are under-ground endogenous stems, covered with scales. In the Banana (Fig. 86), as well as in the Asparagus, the true stem is subterranean, and sends up shoots bearing leaves, flowers, and fruit, which, after dying down, are succeeded by other shoots. The peripheral portion of some subterranean endogenous stems, as Sarsaparilla, presents a circle of vascular wedges, resembling in appearance the stem of certain exogens; and the false bark of some aerial endogenous stems, as Testudinaria, becomes much thickened by the formation of cellular matter resembling cork.

c. Acrogynous Stem, or the Stem of Acrogynous Plants.

This stem, in its complete development, is seen in the Tree-ferns of foreign countries. It resembles the Endogenous stem in being unbranched, and in producing a crown of leaves at its summit. The Tree-fern form gives a peculiar aspect to the vegetation of the countries in which it occurs. The structure of the stem, which is called a candex, consists of cells and vessels, arranged in a peculiar manner. The vascular bundles are formed simultaneously. They consist of woody tissue, often of a dark colour, surrounding a paler layer of vessels, chiefly scalariform, and dotted. The bundles assume various shapes, giving rise to the zig-zag appearance, presented in a transverse section, as seen in Figure 87. The bases of these leaves (or fronds as they are called) by their union form the stem, which is increased by additions to the summit; hence the name given of Acrogynous, or summit-growers. The growing point is carried upwards by the leaves, and when once formed the stem increases very little in diameter. It is often hollow by the rupture of the internal cellular portion. On its outside the scars of the leaves remain (Fig. 88), with the markings of the vascular bundles. These bundles follow a course similar to that of the woody tissue of the liber of Exogens. The stem of Tree-ferns, then, is of moderate diameter, and does not produce lateral buds. Sometimes it terminates in two buds, which, by their growth, produce a forked stem. In the stems of the ordinary ferns of this country the acro- genous structure is seen, although they seldom attain any height, but usually creep along the ground, forming rhizomes.

The acrogenous stem occurs in Horsetails, in Clubmosses, and in true Mosses, but in these plants it does not exhibit the same marked characters as in the permanent woody stems of Ferns. Many acotyledonous plants produce stems which consist entirely of cellular tissue without any admixture of woody fibre or vessels. Such stems are either aerial or subterranean. They often present a flattened expansion or thallus lying on the surface of the ground. Sometimes these cellular stems float in water, as in the case of Sea-weeds; at other times they creep under ground, or among the tissues of other plants, as in the case of Fungi. The spawn (mycelium) of Fungi is a sort of cellular creeping stem, which insinuates itself among the dead tissues of plants and other decaying substances. The cellular stalk of some Thallogens occasionally presents, on a transverse section, an appearance like that of an Exogenous stem. Thus Lepidium fuscescens, a species of sea-weed, has stems which are often five to ten feet long, and as thick as the human thigh, and which show concentric elliptic cellular rings. Such is also the case with Usnea melaxantha, a tree-like lichen. In these plants, however, the structure is entirely cellular, and quite distinct from that of Exogenous plants.

III. THE LEAVES AND THEIR MODIFICATIONS.

Leaves proceed from the nodes of the axis, and commence as cellular processes at the extremities of the medullary rays. In the progress of development the cells multiply, vessels are produced which ramify in the form of veins, chlorophyll is elaborated, and the foliar or leaf organs are thus completed. These organs usually spread horizontally, so as to expose one surface to the sky and the other to the earth—the surfaces differing in appearance and structure. In some plants, as Alstroemerias, the leaf is twisted naturally upon itself, so that what should be the under surface becomes the upper. Erect or vertical leaves occur, in which both sides are equally exposed to light. In some New Holland plants the leaf-organs present their edges to the earth and sky.

1. Arrangement of Leaves on the Axis.

The mode of arrangement of leaves on the stem has been denominated Phyllotaxis (φύλλον, a leaf, and ἀρχή, order). It is regulated by certain definite laws, and depends on the development of the nodes and internodes of the stem and branches. When the internodes are so short that the stem is apparently wanting, the leaves are denominated Radical,

*Pl.CXXIV as in the Cowslip, and in the Dandelion.* In such cases there is often at first sight some difficulty in determining the leaf-arrangement. When the internodes are elongated, and the nodes thus separated from each other, then the phyllotaxis is easily seen.

Each node is capable of producing a leaf or leaf-bud. When each of the nodes on an elongated axis produces a single leaf, the leaves are said to be Alternate (Fig. 89), because they are placed alternately on different sides of the axis. When two leaves are produced at a node, they are called Opposite (Fig. 90), because they are situated on opposite sides of the axis; while the production of three or more leaves at a node gives origin to a circle or whorl of leaves, which are then said to be Verticillate (Fig. 91).

Alternate Leaves.—This arrangement is a very common one, occurring generally in Monocotyledons, and also being frequent among Dicotyledons.* The simplest arrangement *Pl. CXXV. fig. 2.

is that in which the third leaf is placed directly above the first, while the second is placed on the opposite side of the stem, separated by half the circumference of the circle. In this case there are two rows of leaves, one on each side of the stem, and the arrangement is said to be Distichous (δις, twice, and ἄξων, a row). When the fourth leaf is above the first, on the same principle of the leaves being placed at equal distances on the axis, the arrangement will be Tristichous, or in three rows, each leaf being separated from that next to it by one-third of the circumference of the circle. If the fifth leaf is placed above the first, the arrangement will be Tetrastrichous, or in four rows; if the sixth leaf, Pentastichous, or in five rows. The last-mentioned arrangement is delineated in Figure 92, which represents the branch of an oak with six alternate leaves, the sixth being placed vertically over the first.

It will be observed that, in following the course of the alternate leaves on the stem, we proceed in a spiral or screw-like manner, and that the termination of the spiral cycle is to be found in the leaf directly above that from which we commenced. On reaching it the cycle begins again, and goes through the same course as regards the number and arrangement of the leaves. Thus, in Figure 92, the cycle ends at the sixth leaf, which, in fact, commences the new spiral coil. In completing this spiral cycle we may make a single turn round the stem, as in distichous leaves, or we may make two or more. Thus, in the pentastichous cycle we make two turns round the stem, and encounter five leaves besides the first (Figs. 89 and 92). The arrangement has, therefore, been marked by a fraction, of which the nu- Botany.

The Phyllotaxis indicates the number of turns round the stem, and the denominator the number of leaves in the cycle. This fraction at the same time gives the angular divergence of the leaves, or their distance from each other, expressed in parts of the circumference of the circle. Thus the fraction $\frac{1}{2}$ indicates distichous leaves, where the angular divergence is one-half of the circumference of the circle, or $180^\circ$; the fraction $\frac{3}{4}$ implies tristichous leaves, where the angular divergence is one-third of the circumference of the circle, or $120^\circ$; the fraction $\frac{5}{6}$ applies to the Pentastichous or Quincuncial arrangement (Fig. 89), a very common one among Exogens, in which the sixth leaf is immediately over the first, and two turns of the circumference are made before coming to it, the angular divergence being $144^\circ$.

The alternate phyllotaxis, and the angular divergence of leaves is explained more fully by Figures 93 and 94. In these it is shown that, in the case of alternate leaves, perpendicular lines may be drawn through the leaves placed directly over each other, and that the number of these lines indicates the number of leaves in each spiral cycle, or the number of leaves between any leaf on the stem and that directly above it. In both these Figures it will be seen that the number of these lines is seven, and this, consequently, is the number of leaves in each cycle. It is, therefore, a Heptastichous cycle, ending with the eighth leaf which commences the new spiral coil. But it will also be noticed that the number of turns made round the stem in completing the cycle is different. Thus, in Figure 93, commencing with leaf No. 1, we reach leaf No. 8, or that directly above 1, after making three turns round the stem, and the fraction indicating this is $\frac{3}{7}$; whereas, in Figure 94 we reach No. 8 after one turn, and the fraction, therefore, is $\frac{1}{7}$. These fractions mark the angular divergence between any two leaves of the cycle, as represented in the divided circles at the upper part of the stems. In Figure 93, between 1 and 2 the angular divergence is obviously $\frac{3}{7}$ of a circle, or $\frac{3}{7} \times 360^\circ = 154^\circ$, while in Figure 94 the divergence is $\frac{1}{7}$ of the circle, or $\frac{1}{7} \times 360^\circ = 51^\circ$.

Among the common arrangements of leaves may be noted, $\frac{1}{2}, \frac{2}{3}, \frac{3}{5}, \frac{5}{8}, \frac{8}{13}, \frac{13}{21}$, and $\frac{21}{34}$. On looking at these fractions, it will be seen that they bear a constant relation to each other, for the numerator of each fraction is equal to the sum of the numerators of the two preceding fractions, while the denominator is the sum of the two preceding denominators; and the numerator of each is likewise the denominator of the next but one preceding. In the case of stems with marked internodes, with few leaves in the cycle, and with the points of insertion small, these arrangements can be easily detected; but when the internodes are much shortened, and the leaves are very numerous, it is difficult to trace the arrangement.

There is thus a general tendency to alternation in the foliar arrangements of plants, and when they grow regularly the law of phyllotaxis can be ascertained correctly. The arrangement, however, is often much altered by interruption in growth, and other causes, so that we cannot in all cases detect its normal condition. The Phyllotaxis is uniform in the same species, but it frequently varies in species of the same genus. Thus, in the European Larch it is $\frac{3}{5}$, while in the American Larch it is $\frac{8}{13}$. The spirals proceed either to the right or to the left. The phyllotaxis of the branches is usually the same as that of the axis, and it is then called homodromous (εικός, similar, and ἀπόκοσμος, course); but sometimes it is different, and called heterodromous (εικός, diverse).

In typical arrangements, such as those noticed, there are always certain leaves placed directly over others in a straight series, the angle of divergence dividing the circumference into an exact number of equal parts. Such leaves are Reciserial, and are considered as being normal. Cases, however, occur, in which the angle of divergence is such, that it is not possible to divide the circumference by means of it an exact number of times, and hence no leaf can be exactly placed above another. Such cases are called by Bravais Curviserial, being disposed in an infinite curve, and hence incapable of being placed in straight rows.

Opposite and Verticillate Leaves.—In these arrangements two or more leaves are given off as a node. There is here also a tendency to alternation and spiral arrangement as regards the pairs and whorls. Thus, in Opposite leaves, the second pair is not directly above the first, but is placed either at right angles (Fig. 90), and then called Decussate, as in the Mint tribe; or slightly to one side, so that the third, or some higher pair of leaves, is that which is superimposed over the pair with which we commence, as in the Box and in Purging Flax.* In Verticillate leaves, as in Galium and *Pl. CXV., Madder, those of the second whorl are not directly over those of the first whorl, but are so situated as to be above the intervals between the leaves of the lower whorl.

The arrangement of the leaves furnishes characters in some families of plants. Thus, the Cinchona-bark tribe have opposite leaves; the Borage tribe alternate; Labiate plants, opposite and decussate; the Madder tribe, verticillate or whorled. The arrangement of the leaves, however, is not always constant, and we occasionally meet with alternate and opposite leaves in the same plant. In some instances this anomaly may be traced to a non-development of the internodes, by which two or more single-leaved (unifloral) nodes are brought together. Thus, in Rhododendron ponticum, the alternate leaves, by such an arrestment, are sometimes seen almost verticillate. Again, in such plants as the Larch, Cedar, and Pine, the arrestment of the internodes, according to a certain natural law in their development, gives rise to clustered or fascicled leaves.

In the embryo state of dicotyledons, the leaves or cotyledons are opposite; while in monocotyledons the production of one leaf at the node shows the tendency to alternation. The early cotyledonary leaves are called Seminal; those afterwards produced, and constituting the ordinary leaves, are called Primordial. Leaves inserted on a shortened stem close to the ground, have been already noticed as Radical, those on the main axis are Cauline, on the branches, Ramal, and on the flowering stalks, Floral.

Vernation, or Prefoliation.—These names are applied to the arrangement of the leaves in the leaf-bud, and include both the mode in which each leaf is folded, and the relation which the leaves bear to each other. The leaf-bud is produced in the angle where a leaf joins the stem; it contains the growing point of the stem or branch, with its leaves and Botany.

Certain protective appendages called scales, tegmenta or perulae. These scales or outer leaves are often of a coarse nature, covered with resinous matter, and arranged differently from the leaves in the interior, as may be seen in the common Sycamore.

The individual leaves in the bud are folded and rolled up in different ways. When the leaf is folded from its midrib, so that its halves are applied with their upper surfaces towards each other, as in the Oak and Magnolia, it is Conuplicate (Fig 95); when the apex is bent towards the base, as in the Tulip-tree, it is Rectinate, or Inflexed; when folded like a fan, as in the Maple and Vine, the leaf is Plaited, or plicate (Fig 96); when the leaf has each of its edges rolled inwards towards the midrib, as in the Violet and Water-Lily, the vernation is Involute (Fig 97); when outwards, as in Rosemary and Azalea, Revolute (Fig 98); when the leaf is rolled from one edge into a single coil, with the other edge exterior, as in the Apricot and Plantain, it is Convolute (Fig 99); when rolled from apex to base like a crosier, as in Ferns and Sundew, it is Circinate (Fig 100).

The relative position of the leaves in the bud gives origin to the following terms:—Valvate, when leaves are placed in a circle, so as to touch each other at their edges only, without overlapping; Imbricate, when the outer leaves successively overlap the inner to a greater or less extent (Fig 101). These kinds of vernation occasionally become Twisted or Contortive. When involute leaves are applied in a circle without overlapping the vernation is Involute; and when the half of one conduplicate leaf covers half of another, the term Half-equitant or Oboluate is applied (Fig 103); when a convolute leaf incloses another which is rolled up in a similar manner, the vernation is Superoluate (Fig 104).

2. Anatomy or Structure of Leaves.

The leaf consists of a cellular and vascular portion; the former constituting the Parenchyma—the latter the Ribs and Veins. The whole is covered by an integument. The flat expanded portion is called the Lamina, blade or limb (Fig. 105, f), consisting of cells traversed by vessels, and the narrow portion is called the Petiole, or leaf-stalk (Fig. 105, p), in which the cellular tissue is less abundant, and the vessels are more closely united. At the base of the petiole there are sometimes certain leafy appendages denominated Stipules (Fig. 105, s). The petiole is sometimes wanting, and the leaf is then Sessile; at other times the blade is transformed, so as to appear like a petiole. The leaf may be denominated a flattened expansion of the green layer of the bark, strengthened by woody fibres and vessels. The Parenchyma varies much in its extent, and in the form of its cells. In fleshy leaves it is abundant, and its cells are loose, and more or less rounded. In an ordinary flat leaf there are two surfaces, one of which (the upper) is exposed to the light. The epidermis covering these surfaces consists of compressed colourless cells. That of the lower surface is often of a paler colour, and is provided with stomata and hairs; while on the upper side the epidermis is more tough and dense, and is either entirely destitute of stomata, or possesses them in small number. In leaves placed vertically, the stomata sometimes exist in equal number on both sides; in floating plants, as Water-Lilies, the stomata exist only on the upper surface of the leaf; while in submerged leaves no stomata occur on either surface, and the true epidermal layer of cells is absent. De Mercklin states, that leaves have their origin in cellular papillae arising from the axis. Their apex is the first part formed, and it is pushed forward by the growth of the part below. The leaf-stalk is formed after the blade, the lower part of it being the last developed. Leaves are undivided in their early state; all the divisions which take place in them are subsequent formations. The mode in which the parenchyma increases, and the arrangement of the veins, give to the leaves their varied forms.

Parenchyma.—In ordinary leaves, this consists of two distinct layers of cells, one connected with the upper surface (looking to the sky), and consisting of compact oblong cells, placed endwise (Fig. 106, ps); the other, connected with the lower side, consisting of loosely-aggregated cells, having numerous cavities between them (Fig. 106, pn), and, when of an elongated form, placed with their long diameter parallel to the epidermis. The cavernous nature of the lower epidermis seems to be connected in some degree with the stomata and their functions. The cells on the upper side are usually placed close to each other, without any space between them, except in cases where stomata occur (Fig. 106, st). Sometimes there are several layers of epidermal cells, more particularly in plants exposed to the heat of the tropical sun, as the Oleander. The parenchyma is occasionally deficient at some parts of leaves, giving rise to deep indentations or to perforations. In Monstera pertusa there are distinct holes in the leaves; and in an aquatic plant of South Africa (Ouvirandra fenestralis), the tissue of the leaf Botany.

is made up of interlacing filamentous cells, with perforations between them, giving the appearance of a skeleton leaf. In Victoria regia there are peculiar perforations in the leaves. The surface of leaves is sometimes smooth (glabrous), at other times hairy (hirsute), downy (pubescent), or woolly. The hairs are either lymphatic or glandular. In the case of the Sundews (Drosera) the leaves are fringed with glandular hairs (chlamyds), and their surface is covered with them (Fig. 107); while in Venus's Fly-Trap (Dionaea muscipula) there are irritable hairs on the leaves, which, when touched, cause the two sides of the leaf to fold together.

Vascular system.—This consists of a double layer of vessels which may be separated by maceration. It is composed of woody, laticiferous, dotted, and various kinds of spiral vessels. These vessels collectively form the petiole or stalk of the leaf, and spread out in the lamina or blade, so as to constitute the veins. When a leaf is macerated, the cellular tissue is separated, and the vascular bundles alone remain. In some leaves, as in the Barberry, the vessels forming the veins are hardened, producing spines without any parenchyma. The hardening of the extremities of the vascular tissue is the cause of the spiny margin of many leaves, such as the Holly, of the sharp-pointed leaves of Madder, and of mucronate leaves, or those having a blunt end with a hard projection in the centre.

The firm and prominent bundles of vessels in the leaf are called Ribs (costae), and others less conspicuous are denominated Veins. The term Nerve, as applied to the vessels of the leaf, is now generally given up to avoid ambiguity as to function. In (Fig. 108) there is given a representation of a vertical section of a branch, showing the mode in which the vascular bundle, f r, gives off a prolongation to the leaf-stalk, f. The vessels pass from the sheath surrounding the pith, m, through the parenchyma, p e p e, and communicate with the young bud, b, in the axil of the leaf.

Venation.—This term has reference to the arrangement of the vascular tissue of the leaf. There are two marked forms of venation, one in which the vessels from the petiole or stem, on entering the leaf, are continued in the form of one or more ribs, which give off branches on either side, and form an anastomosis or net-work of vessels (Fig. 109); the other, in veins or ribs, which run more or less parallel to each other, and are united by simple transverse veins, as in Palms (Fig. 110), grasses, and the leek (Fig. 111); or in which the midrib gives off lateral veins which run parallel, as in the Banana (Fig. 86). The former are Reticulated or Netted leaves, and are common in dicotyledons, while the latter are Parallel-veined, and are characteristic of monocotyledons.

In reticulated leaves there is either one primary rib called Midrib, or there are several prominent ribs, as in Cinnamon. When a single midrib is present it gives off branches or veins, which either proceed directly to the margin, as in the Feather-veined leaves of the Oak (Fig. 92) and Chestnut, or which end within the margin in curved veins, as in Lilac and Dead-nettle (Fig. 109); in the latter case, marginal veinlets proceed from the curved veins. When there are three prominent ribs, as in Cinnamon, the leaf is Tricostate; when five, Quinquecostate. When the midrib gives off two ribs a little above the base, the leaf becomes Triplicostate; when it gives off five, Quintuplicostate.

In a many-ribbed leaf, the ribs may converge towards the apex, as in Cinnamon, or they may diverge. In the latter case they are said to radiate, and they give origin to Palmate and Palmatifid leaves, as in the Sycamore. Parallel-veined leaves have either a single midrib, the veins from which come off in a parallel manner, and run to the margin without forming a net-work, as in the Bananas (Fig. 86), and Indian Shot (Camna); or they have numerous veins or ribs running from base to apex (Fig. 111), converging as in Grasses and Lilies; or diverging, as in Palms (Fig. 110).

In very succulent plants, as the American Aloe (Agave americana), and Fig-Marigolds, where the parenchyma abounds, the veins are obscure, and in plants such as Mosses and Sea-weeds, the so-called veins are composed of an aggregation of long cells, without any woody fibre. In many plants belonging to the Myrtle order (Myrtaceae), which have ribbed leaves, there is an obscure vein which runs from the base to the apex of the leaf, close to the margin, and in which the lateral veinlets end. The primary veins come off from the midribs of leaves at different angles, and thus contribute to give form to the leaf. Primary veins coming off at a very acute angle, and converging, give rise to narrow leaves; those proceeding more at a right angle frequently produce broad leaves; while those coming off at obtuse angles cause prolongations at the base of the leaf. So also with veins radiating from a point, their greater or less divergence gives origin to leaves of a broader or a narrower form.

The arrangement and form of the foliaceous appendages of plants depend much on the number, the development, and the relation of the fibro-vascular bundles of the stem. In vascular plants the skeleton of the leaf is formed by an expansion of the fibro-vascular bundles of the stem. The leaves contain vessels similar to those forming the bundles at the point where they escape from the axis. The vascular bundles, as well as the parenchyma of the stem, expand in the leaf in various ways.

M'Cosh thinks that the venation of leaves bears an ana- logy to the distribution of the branches, so that the leaf and its veins represent the stem and branches of the plant. He considers that in plants there are three homotypal parts, morphologically allied, and representatives of each other, viz., the root and its ramifications, the stem and its branches, and the leaf with its veins. These parts he looks upon as typically analogous. He has carried out his researches chiefly in regard to reticulated leaves. The angles at which the veins are given off, he considers as being the same as those at which the branches come off, and he has attempted to prove this position by numerous measurements of angles. In trees there is a certain normal angle at which branches are given off, producing a peculiar physiognomic effect. This angle may be much modified by circumstances, and it may vary according to the age of the branches. The determination of this angle is a point to which M'Cosh calls attention, and his researches lead him to adopt the view that the same angle will be found to prevail in the leaf-formation.

3. Conformation of Leaves.

With few exceptions, every plant has leaves at some period of its growth. Even those which produce leafless stems have generally seed-leaves (Cotyledons) in their embryo state. The Dodders* and a few other plants, are exceptions to this rule. Leaves present various forms, from the scales of Broom-rapes, and the linear leaves of Asparagus and Pines, up to the large foliar expansions of the Banana, and of the Talipot Palm. To the nature of the venation and the development of parenchyma all the leafy forms must be traced. Leaves are usually arranged under the heads of Simple and Compound; the former having a blade composed of one piece, and having no articulation beyond the point where they join the stem, as in the Oak (Fig. 92); the latter having a blade divided into separate pieces or leaflets, which are articulated with the petiole (Fig. 112).

Simple Leaves.—These, although formed of one piece, may have their blades variously divided, provided the separate portions are not supported on stalks, nor articulated to the petiole, nor to the midrib. In their very young state they are entire or undivided, and equally developed. When they increase more on one side than on the other, they become either oblique, as in the Begonia and Lime (Fig. 105), or slightly unequal at the base, as in Senna (Fig. 125); and when the cells and vessels increase and elongate only at certain points, divisions take place in the margin of the leaves, and in the substance of their laminae.

In the circumscripture or margin of the leaf, the following varieties occur:—Entire, without any divisions (Fig. 113); Crenate, with superficial rounded divisions (Fig. 114); Serrate, with acute points, arranged like the teeth of a saw (Fig. 109); Dentate, with similar pointed projections, not arranged in a saw-like manner; Repand and Undulated,*PL.CXXIII when the margin is wavy and sinuous, or, as it is often called, crisp, as in curled leaves; sometimes, as in the Holly, the leaf is undulated, with spiny teeth. When the apex of a leaf is blunt and rounded, it is called Obtuse (Fig. 115); when sharp, and forming an acute angle, it is Acute (Fig. 113). The apex is Abrupt or Truncate, when it is terminated by a straight transverse line, as in the Tulip tree; Re- tuse, when it is rounded and slightly depressed; Emarginate, when there is a deficiency or notch at the apex (Fig. 116); Obcordate, when the deficiency is very evident, and the lobes large, so as to resemble an inverted heart on cards. When the apex is drawn out into a long point, as in Ficus religiosa, the leaf is Acuminate or pointed; when the apex is blunt, and presents a stiff hard point, it is Mucronate.

When the substance of the lamina is divided to about the middle, the terms Cleft (in composition fad) and Lobed are applied; and when the division extends to near the base or midrib, the term Partite is used. These divisions, occurring in a radiating-veined leaf, give origin to the terms, bifid (twice cleft), trifid (thrice cleft), quinquefied (five-cleft), and multifid (many-cleft); also to the terms bilobate (two-lobed), trilobate (three-lobed), &c., when the divided portions of the leaf are large; and tripertite (Fig. 117), quinquepartite (Fig. 118), and multipartite, when the divisions extend to the base; Palmate (like the palm of the hand), when there is a broad lamina, divided into five parts, as in some species of Passionflower; Palmatifid, or Palmately-cleft, when the divisions are more than five, as in Castor oil (Fig. 119). The terms palmate and palmatifid are, however, often used indiscriminately to mark a leaf. Botany.

having a broad portion like the palm of the hand, and either five or more lobes.* When the parts of a pinnatifid leaf are narrow, like the fingers, the term *digitilobed*, and Fig. 1.

*Pl. CXIV.* dissected, are applied; and when they are cut into thread-like divisions, as in the submerged leaves of Ranunculus aquatilis, they are said to be *filiformly dissected*. The term *Pedate* (like the foot of a bird) is applied when the lateral divisions of a three-lobed leaf are again divided, as in stinking Hellebore* (Fig. 120).

In a feather-veined leaf similar divisions give origin to the terms *Pinnatifid*, with large lateral divisions, as in the Oak (Fig. 92); *Pectinate* (comb-like), with very narrow divisions; *Pin natipartite*, when the divisions extend near to the midrib (Fig. 121); *Pinnately-divided*, when the divisions extend to the midrib. When the primary divisions of


such leaves are again subdivided in a similar way, the terms *bipinnatifid* and *bipinnatipartite* (Fig. 121) are applied; and when not only the primary, but also the secondary segments are divided in a similar way, the terms *tripinnatifid* and *tripinnatipartite* are used. In a pinnatifid leaf it sometimes happens that there are few divisions, in consequence of the lobes at the apex or base being united, thus giving rise to the *Lyrate* leaf (like an ancient lyre), with a large terminal lobe, and segments becoming smaller as they approach the petiole (Fig. 122); and the *Panduriform*, when the lobes have a recess or sinus between them, so as to make the leaf resemble a violin. When the divisions of a lyrate-pinnatifid leaf have acute terminations, and point downwards, as in the Dandelion, the term *Runcinate* is applied (Fig. 123).

In the case of reticulated leaves, the angle which the veins form with the midrib, and their comparative lengths in different parts determine in a great measure the contour of the leaf. The following are some of the usual terms employed:

—*Linear*, when the leaf is narrow, and the veins proceeding from the midrib are very short, and nearly equal. When linear leaves are sharp-pointed, as in Pines and Juniper, they are called *Acrose*; when linear leaves taper, so as to be like an awl, they are called *Subulate*; leaves are *Oblong*, when the veins from the midrib are longer than in linear leaves, but still nearly equal, and the apex is rounded (Fig. 112); *Rounded* and *Elliptical*, when the veins from the centre of the midrib are longest, and the forms approach more or less to the circle or ellipse.

When the veins coming off from near the base are the longest, and the leaf has the shape of an egg, it is called *Ovate* (Fig. 124); it is *Oborate* (inversely egg-shaped) when the veins at the apex are longest, and the leaf is thus like an ovate one reversed (Fig. 116); when the apex of an obovate leaf is straight, or not uniformly rounded, it becomes *Cuneiform* (wedge-shaped); when an obovate leaf, with a round apex, tapers to the base, as in the Daisy, it is called *Spathulate*; a leaf is *Lanceolate* (Fig. 125) when the veins near the base are longer than those above and below, and the leaf tapers towards the apex; *Ovato-lanceolate*, when the general form is lanceolate, but the base is broad (Fig. 113).

When the lower veins come off at an obtuse angle from the midrib, and are curved back so as to form with the parenchyma two large round lobes at the base, with a narrow recess or sinus, like the heart on cards, the leaf is *Cordate* (Figs. 105 and 109); it Botany.

is *Reiform* when the recess is large, and the contour rounded, so that the leaf resembles a kidney (Fig. 114); *Sagittate*, when the lobes of a cordiform leaf are acute, so as to resemble the head of an arrow, as in species of Convolvulus (Fig. 126), and Arum; *Hastate*, when the lower veins proceed nearly at right angles, and form two lateral narrow lobes, as in Rumex Acetosella (Fig. 127); *Auriculate*, when the lobes at the base of a hastate leaf are separated from the lamina, so as to be distinct segments; *Deltoid-hastate*, when a hastate leaf is short, and resembles the Greek letter delta, as in Ivy. Sometimes a leaf cordate at the base (next the petiole), has a rounded contour, and it becomes *Rotundato-cordate* (Fig. 128, a).

The lobes at the base of leaves are sometimes united more or less completely, thus giving rise to the *Peltate* or *Shield-like* form, as in the Indian Cress (Fig. 128, b), and Castor oil (Fig. 119); and the *Orbicular* form, when the petiole is attached in the centre of a large rounded leaf, as in Pennywort (Hydrocotyle vulgaris) and Victoria regia. Very succulent leaves, with obscure veins, assume certain thickened forms, so as to become cylindrical, conical, sword-shaped, Peltate (Shield-like) leaves of Indian Cress (Tropocodon majus).

Simple parallel-veined leaves usually have their margins entire, especially when the veins converge. They assume some of the forms already noticed, such as linear, oval, elliptical, oblong, and ovate. It is comparatively rare to find any marked divisions of their laminae. When the veins diverge at the base, or come off at obtuse angles, we meet with hastate, sagittate, and cordate forms, and their various modifications. In some Palms, where the veins running in straight lines diverge, the margin of the leaf is cut into linear segments of different lengths (Fig. 110). In some Monocotyledons the leaves present a reticulated venation, and they are hence called *Dietegenous* (diverse, a net).

**Compound Leaves.**—These originate, like simple leaves, in the form of undivided cellular projections from the axis. When fully formed, they consist of lamina divided down to the petiole or midrib into distinct pieces or leaflets, which are articulated, more or less distinctly, to the common stalk (Fig. 129). These leaflets (folioli) are either supported on stalklets of their own, or are sessile. Compound leaves may be reduced to two well-marked forms; those formed by the divisions of a feather-veined unicostate leaf, and including the various pinnate forms (Fig. 130); and those traced to the division of a radiating-veined multicostate leaf, including the various digitate forms (Fig. 131).

When there is a distinct midrib giving off primary veins laterally, which are covered with parenchyma in such a way as to form separate articulated leaflets, the leaf is *Pinnate*, as seen in Figure 130, which represents a compound leaf composed of nine pairs (juga), of shortly petiolated pinnae, and an odd leaflet at the end. If a pinnate leaf ends in a pair of leaflets, the extremity of the midrib being either leafless or ending in a tendril or point, the leaf is said to be *Equally* or *Abruptly-pinnate* (pari-pinnate). When there is a leaflet at the point, the leaf is said to be *Unequally-pinnate* (impari-pinnate), as in Figure 130. When a lyrate leaf becomes truly pinnate, i.e., has its divisions articulated to the midrib, it is *Lyrate-pinnate*; and when the leaflets of a pinnate leaf are of different sizes, the term *Interruptedly-pinnate* is applied. Some parallel-veined leaves, as those of the Coco-nut, Date, and Sago Palms, are pinnate.

The number of pairs (juga) of leaflets in a pinnate leaf varies. There may be only three leaflets (Fig. 129), in which case two are lateral, and one is terminal. Such a leaf approaches to the ternate leaf which belongs to the radiating venation, and is distinguished by the distance intervening between the two articulated lateral pinnae and the terminal one. When the leaflets of a pinnate leaf are divided into separate pieces or pinnales, the leaf becomes *Bipinnate* (twice pinnate), as in Figure 132. When the subdivision takes place... Botany.

to a further extent, the leaf becomes either Tripinnate or Decompound.

Compound leaves referred to the radiating venation, i.e.,


Tripinnate (doubly pinnate, twice pinnate), leaf of Gleditscha triacanthos. Each leaflet is pinnate, and the leaflets are called leaflets. It may be said to be a pinnate leaf, with the leaflets also pinnate.

Multicostate with diverging ribs, are distinguished from those referred to the feather-venation, by the leaflets coming off from one point. When the leaflets coming from one point are two, the leaf is Binate or Unijugate (one pair); when three, Ternate or Trifoliolate, as in Woodsorrel and Strawberry; when five, Quinate or Quinquefoliate, as in Hemp; when seven, Septenate or Septemfoliate, as in the Horse-chestnut (Fig. 131). When the leaflets are five, the leaf is often called Digitate. Similar forms may occur among pinnate leaves (Fig. 129), but in them the leaflets will be seen not to come off from the point of the petiole, but at certain distances from each other. In the case of a ternate leaf, the two lateral leaflets may disappear, while the central one remains articulated to the petiole. Some consider this as being the case in the Orange leaf (Fig. 133), which is therefore looked upon as a compound leaf with a single jointed leaflet. A ternate (trifoliolate) leaf may divide in such a way as to form three leaflets on the secondary veins, proceeding from each of its primary veins, and thus become Bitermate (doubly ternate); while a further subdivision, in a similar way, will render it Tritermate (triply ternate).

4. Petiole or Leaf-Stalk.

The stalk supporting the blade of the leaf is denominated the Petiole (Fig. 105, p.). It is absent in the case of sessile leaves; and, in certain instances, the distinction between the lamina and the stalk is not well defined. The petiole consists of a definite number of vascular bundles enclosed in a small amount of parenchyma. The vessels are woody, dotted, spiral, and laticiferous, and they are derived from the internal part of the stem, as shown in Figure 108, where the vessels, \( f \), surrounding the pith, \( m \), are traced into the leaf-stalk, \( f \).

At the point where the vessels leave the stem there is often a small enlargement (pulvinus), composed of cellular tissue, and an articulation or joint. When the leaf dies, it separates from the stem at the joint, leaving a mark or scar (cicatrix, cicatricula) in which the ends of the different vascular bundles are seen arranged in a definite order. The form of the scar, and the arrangement of the bundles, differ in different plants, and furnish, in some instances, distinct characters. In the case of many Palms, and of Tree-ferns, the scars left by the leaves are very conspicuous.

When there is no articulation between the petiole and the stem, as is the case with many Endogens, the leaf is continuous with the axis, and is not deciduous, but withers on the stalk. In many Liliaceous plants, the leaves during their decay continue attached to the plants. In compound leaves there is usually an articulation, where the leaflet or leaflets join the petiole. At this joint also a cellular swelling (struma) occurs. In many pinnate leaves, as those of the Sensitive plant, the axial and foliolar joints and swellings (pulvinus and struma) are very evident. Where the petiole joins the blade its vessels diverge, so as to form the ribs and veins—the vascular bundle which continues in the direction of the stalk being the midrib. The epidermis of the petiole has few stomata.

The petiole is usually either round, or half cylindrical, with a flattening or grooving on the upper surface. In the Aspen it is compressed laterally, or at right angles with the blade and hence the trembling of its leaves from the slightest breath of air. When the leaves of a plant float in water, the petiole is sometimes distended with air cavities, as in the Water Chestnut. The edges of the petiole in plants such as the Orange (Fig. 133), the Quassia plant, Venus' Fly-trap, the Sweet Pea, and other species of Lathyrus, are bordered by a leaf-like expansion called a Wing, and hence they are denominated Winged or Bordered petioles. Such leafstalks are occasionally united to the axis for some extent, and thus become Decurrent. In many Endogens, especially grasses, the leaf-stalk forms a Sheath round the stem; this sheath in grasses terminates at the upper part, in a process called a Ligule, as seen in Figure 134, where \( g \) is the sheath (vagina), \( l \) the blade of the leaf, and \( h \) the ligule. In Umbelliferous plants* the petiole is expanded, and forms a conspicuous sheath round the stem. This sheathing portion of the petiole is formed by the divergence of the vascular bundles on either side. The vessels thus surround the stem, and are covered with parenchyma. This petiolar sheath may be considered as a modification of stipules.

In some Australian plants belonging to the genera Acacia and Eucalyptus, the petiole is flattened, and becomes a foliar expansion, which occupies the place of true leaves. Such petioles have received the name of Phyllodia (φύλλον, a leaf).

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Fig. 134. Stem of a Grass (Poa) with leaf. The sheathing petiole, \( g \), ending in a process, \( h \), called a ligule; the blade of the leaf, \( l \).

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Fig. 135. Leaf of an Acacia (Acacia acutissima), showing a flattened leaf-like petiole called a phyllodium, with straight venation, and a bipinnate lamina, \( l \).

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The trees bearing them give a peculiar character to some forests in New Holland. These phyllodia are usually placed vertically, presenting their edges to the sky and earth, and their venation is parallel. They occasionally bear pinnate or bipinnate laminae, and in such cases they are frequently much narrowed in their dimensions. In Figure 135 a bipinnate leaf is represented, with its flattened petiole or phyllodium, the venation of which is straight. On the same tree may be seen naked and leaf-bearing phyllodia. By this, as Botany, well as by their venation, their petiolar character is determined. Trees producing naked vertical phyllodia only have a singular effect as regards light and shade. Some shrubby species of Wood-sorrel exhibit phyllodia, which are either naked, or bear ternate leaflets.

5. Stipules or Stipulary Appendages.

Stipules are leafy appendages situated at the base of the petiole, and having normally a lateral position as respects the leaf. They have usually the same structure as leaves, and, in some instances, as in Lathyrus Aphaca, they constitute the only leaves which the plant produces. In the Pansy (Fig. 136), they are as conspicuous as the ordinary leaves. In the Pea, they are also large, and in many of the pea tribe they assume peculiar sagittate forms. Stipules are not present in all plants. Those having stipules are called Stipulate, those without stipules are Exstipulate. At a certain stage of their growth, some stipules are larger than the leaves or leaflets produced before them. Thus they serve as a protection to the leaves in the young state, as in the India-rubber Fig, Potamogetons, Magnolias, and the Beech. These protective stipules generally fall off when the leaf expands.

The form and appearance of stipules vary; some are leaf-like; others cirrhose; some are small, others large; some assume a scaly or membranaceous appearance, others are hard and spiny; some are separate and free, others are united. In this way the nature of the stipules gives characters in many natural orders. In the Cinchona bark trees, which have opposite leaves, the stipules unite, so as to form of the stem between the petioles, hence they are called Interpetiolate. In the Rhubarb tribe, which have alternate leaves, the stipules unite, so as to form a sheath or Ochrea round the stem. In the Plane tree, and in the Astragalus, they unite, so as to form a leafy expansion on the opposite side from the leaf; and in the Rose tribe they are united to each other and to the petiole, thus becoming adnate. The petioles of many plants have a sheathing portion at their base (Fig. 117), which may be considered as adherent stipules. On this account the reticulum, or mat-like substance, at the base of the leaves of palms, is often called stipular. Besides the leaves at the base of the petiole, smaller leaflets (stipels) are occasionally produced at the base of the pinne of compound leaves, as in the bean.

6. Transformations of Leaves and their Appendages.

Some of these transformations have been already noticed, but there are others to which it is necessary to direct attention. The morphological relations between leaves, scales, and spines—between petiole and lamina, and between stipules and petioles, have been adverted to. All these nutritive organs are sometimes changed into tendrils (cirri), with the view of enabling the plants to twine round others for support. In Leguminous plants (the pea tribe) the pinnae are frequently cirrhose. Sometimes a whole leaf becomes cirrhose, as in some species of Lathyrus. In Smilax there are two stipular tendrils, while in the Cucumber tribe there is a single one at the base of each leaf. In the Passionflower the lateral leaf-buds, and in the Vine the terminal ones, become tendrils.

The leafy parts of plants are also liable to become hardened and spineous. The leaves of some species of Astragalus and Barberry, and the stipules of the False Acacia (Robinia) are spiny. In these instances the vascular bundles are developed in a marked degree, while the parenchyma is deficient. To the same cause is attributed the spiny margin of the Holly-leaf. In the Gooseberry, the swelling (pulvinus) at the base of the petiole, and below the leaf, assumes a spinose character.

Changes in the appearances of leaves are produced by adhesions and foldings of various kinds. When two leaves unite at their bases, as in some species of Honeysuckle (Fig. 137), they are called Connate. When the lobes at the base of a leaf unite on the opposite side of the stem from the lamina, a Perfoliate leaf is the result, as seen in some species of Bupleurum (Fig. 138) and Baptisia. The formation of Peltate and Orbicular leaves has been traced to the union of the lobes of a cleft leaf. In the case of the Victoria leaf the transformation may be traced during germination; the first leaves produced by the young plant are linear, the second are sagittate and hastate, the third are rounded-cordate, and the next are orbicular. The cleft indicating the union of the lobes remains in the large leaves. Many forms of stipules, such as petiolar, interpetiolar, and sheathing, are traced to adhesion.

Folding of the leafy appendages, and union of their edges, give rise to the formation of a hollow leaf or Pitcher (ascidium, ascus). In the Side-saddle flower the ascidia are considered as being formed by the petiole or phyllode, a part of which, in an unadherent state, is prolonged upwards (Fig. 139). In the Pitcher-plant there is an evident lid, united to the pitcher by a joint (Fig. 140). The lid is looked upon as the metamorphosed lamina, articulated to the hollow petiole or phyllode. It may be said to resemble the jointed leaves of the Orange, or Dionaea, with their petioles folded so as to adhere by the edges, and their laminae reduced in size, so as to form a lid (operculum).

The hollow (fistular) leaves of the onion, and of other species of Allium, may... Botany. be traced to the folding and adhesion of the margins of the foliar appendages.

It has been already remarked, that buds and bulbils are produced at the points where leaves join the stem. In some instances, however, we find that buds are produced from the margins or surfaces of leaves. In Bryophyllum (Fig. 141), this is a common occurrence, and it is met with in many plants of the order Gesneraceae; the leaves of which, when placed on the surface of moist earth, become what is called proliferous, or bud-bearing.

II.—PHYSIOLOGY OF THE NUTRITIVE ORGANS.

I. CHEMISTRY OF VEGETATION.—CONSTITUENTS OF PLANTS, AND SOURCES WHENCE THEY ARE DERIVED.

It is impossible to study the functions of plants without knowing their chemical composition, and the sources whence they derive the materials necessary for carrying on their vital processes. Hence, before proceeding to consider the plant in a state of activity, and as performing vital actions, it is necessary to give a general view of the Chemistry of Vegetation. This subject has engaged the attention of many distinguished chemists, among whom may be mentioned Saussure, Sprengel, Davy, Liebig, Dumas, Mulder, Boussingault, and Johnston. The subject has assumed importance in an agricultural point of view, and a knowledge of it is essential for carrying on farming operations in an enlightened manner. The theory of manures, and the practical application of them, is intimately connected with the knowledge of the composition of plants and of soils.

1. Organic Constituents of Plants.

The materials of which the substance of plants is composed are of two kinds, Organic and Inorganic. The organic constituents form the great bulk of the tissues of plants; they are completely consumed when the plant is burnt; they are produced by living organs alone, and cannot be manufactured in the laboratory of the chemist. The inorganic constituents, on the other hand, form a small portion of the tissues; they are incombustible, and remain in the form of ash after the organic constituents have been consumed by fire; and they can be produced in the laboratory of the chemist. The former may be called the combustible materials produced by living plants; the latter incombustible materials, found not only in plants, but also in the mineral kingdom. Both are derived originally from unorganized matter, and both enter into the composition of organized structures in a greater or less degree. The vegetable organic constituents are composed chiefly of Carbon (C), Oxygen (O), Hydrogen (H), and Nitrogen (N). The inorganic constituents are composed of metallic bases in combination with oxygen, acids, and metalloids. In the fresh plant there is always a large quantity of water (H₂O). This is removed by drying. The quantity varies in different plants—succulent and fleshy species containing a larger proportion of water than those which are dry and hard.

After the plants have been dried so as to remove the water, an estimate can be made, by burning, of the relative proportion of organic and inorganic matter—the former being dissipated by the action of fire, and the latter remaining in the form of ashes. Boussingault gives the following tabular view of the quantity of Carbon, Hydrogen, Oxygen, Nitrogen, or the organic constituents, and of Ash or the inorganic constituents:

| | Wheat | Oats | |--------|-------|------| | Grain | 46-1 | 48-4 | | Straw | 50-7 | 50-7 | | Grain | 50-7 | 50-7 | | Straw | 46-5 | 46-5 | | Carbon | 49-4 | 49-4 | | Hydrogen | 5-8 | 5-8 | | Oxygen | 5-8 | 5-8 | | Nitrogen | 5-8 | 5-8 | | Ash | 2-4 | 2-4 |

This table shows that the quantity of ash is small, and that the organic elements Carbon and Oxygen are the most abundant. The relative proportions of the different organic elements, it will be seen, vary in different plants, and in different parts of the same plant. Thus nitrogen is more abundant in the grain than in the straw of wheat and oats. It is also more abundant in yellow peas and in clover seed, than in the cereal grains and hay. Some of the organic vegetable compounds consist of Carbon, Oxygen, Hydrogen, and Nitrogen or Azote, and are hence called Nitrogenous or Azotized. Others are composed of Carbon, Oxygen, and Hydrogen, without the addition of Nitrogen, and are hence called Non-Nitrogenous or Unazotized. In considering these constituents, we shall make some remarks on the elements of which they are respectively formed.

a. Non-Nitrogenous or Unazotized Constituents and their Elements.

The organic compounds, denominated unazotized, are important constituents of all plants. Some of them, such as cellulose, lignine, starch, gum, sugar, and oily matters, are universally diffused over the vegetable kingdom. Others, such as vegetable acids, bitter principles, and resins, are more limited in their distribution. All of these substances, except cellulose and starch, which are organized, and gum, which is amorphous, are crystalline when they can be got in a solid state. These unazotized matters, which are still subject to the law of crystallization, do not take part in the formation of tissues. Starch and cellulose, on the other hand, are concerned in the development of the organized parts of plants, but in order to effect this, they require the addition of certain azotized products as well as some inorganic matters. Cells and vessels cannot be formed without the presence of albuminous matter, which contains nitrogen and sulphur in its composition, and which cannot be produced without the presence of phosphates. The physico-vital energies of the plant effect the union of carbon, oxygen, and hydrogen, in different proportions. These elements, existing in certain states of combination in the atmosphere, are within the reach of plants at all times.

Carbon—enters largely into the composition of plants. It is said to form two-thirds of the weight of dried plants in general. This substance is familiar to us in the form of wood-charcoal, and in its purest state it is seen in the diamond. Charcoal is porous, and has the power of absorbing soluble gases in large quantity, of separating saline and other matters from solutions, and of taking away disagreeable odours. When combined with two equivalents of oxygen, carbon forms carbuncle acid (CO₂), and it is in this condition that it is taken up by the leaves and other parts of plants. Some maintain that this carbuncle acid is derived by plants entirely from the atmosphere, which contains about 1-1000th of its volume of the gas. The quantity contained in the air, although it appears small when compared with the whole bulk of the atmosphere, is nevertheless sufficient to supply all the carbon of plants. A room 40 feet long, 24 feet wide, and 16 feet high, will contain in its atmosphere 15 cubic feet of carbonic acid, equal to 28 ounces by weight of carbon.

The leaves of plants have a great power of absorbing carbonic acid. Boussingault proved this by passing air containing the usual proportion of carbonic acid over a vine leaf. Even by coming for a few seconds into contact with the leaf, the air was deprived entirely of its carbonic acid. The carbonic acid in the atmosphere is derived from various sources. Amongst the most evident of these are—1. The respiration and transpiration of man and animals. 2. The decomposition of dead animal and vegetable matter. 3. Various processes of combustion on the surface of the earth. 4. Volcanic action going on in the interior of the earth in different countries.

The function of respiration in animals consists in the giving out of carbonic acid, or, in other words, the oxidation of carbon, while the great function of vegetables is the elimination of oxygen or the deoxidation of carbonic acid. The two processes are antagonistic, and a balance is kept up between the carbonic acid given off by animals, &c., and the oxygen given out by plants. A grown person is said to give off 3½ lb. of carbon in a day, and every pound of carbon burnt or oxidized yields more than 3½ lb. of carbonic acid. While active volcanoes give out carbonic acid, there are also extinct ones which do so. The soil in the country on the Rhine, to the south of Bonn, gives out carbonic acid; and all the waters in that district are charged with it. The carbonic acid of coal arises from the decay of vegetable matter.

When plants decay they furnish to the soil a large supply of carbon in the form of humus or common vegetable mould. This cannot be taken up directly as food by plants, but it is acted on by air and moisture, and undergoes certain changes by which a portion of carbonic acid is probably formed. It also has the power of absorbing gases, such as ammonia, and sulphuretted hydrogen, as well as saline substances, and of making them available for the use of plants.

Oxygen—is another organic element of plants. It is known to us in a gaseous state as forming 21 per cent. of the bulk of the atmosphere, and as supplying materials for respiration and combustion. When one atom of oxygen is combined with one of hydrogen, water is formed, and carbonic acid is the result of the union of one atom of oxygen with two of carbon. In its combinations with metals and metalloids, oxygen forms a large proportion of the solid materials of the globe. All the oxygen in plants seems to be derived from carbonic acid and water. No vegetable contains more oxygen than can be accounted for by these two sources.

Hydrogen—is another element of plants which is known to us in the state of a gas. It does not, however, occur free and in a simple state in nature. It exists in small quantity in animal and vegetable substances, forms 1-9th of the weight of pure water, and enters into the composition of coal. The hydrogen of plants is derived from water.

As carbonic acid and water therefore exist at all times, more or less, in the atmosphere, it appears that the air is the source whence plants procure the carbon, oxygen, and hydrogen, which enter so largely into their composition. At the same time, it cannot be denied, that these elements also exist in the soil, and may be taken up by the roots of plants in the form of carbonic acid and water. The various non-azotized vegetable products (i.e. the products consisting of carbon, oxygen, and hydrogen) can be derived from carbonic acid (CO₂), and water (HO), by a process of deoxidation; and as this process is constantly going on in every plant, by means of which oxygen is given out, we may conjecture that it is in this way that the products are formed.

Another class of substances found in the tissues of plants, and essential to the process of vegetation, consists of carbon, hydrogen, oxygen, and nitrogen (N), with the addition of sulphur (S), and alkaline or earthly phosphates. They are commonly called Nitrogenous or Azotized or Azoto-sulphurized substances. Some authors include them under the general name of Mucus or Protoplasma. The constituents of these organic matters are known by the names of vegetable albumen, fibrine, and caseine. The general name of gluten is given to the glutinous part of wheat which remains after the starch and soluble constituents of the grain have been removed. This gluten consists usually of fibrine and albumen. Wheat contains from 8 to 24 per cent. of gluten; barley 3 to 6; oats 2 to 5.

Nitrogen enters largely into the composition of the tissues of animals, and hence it must be supplied to them in their food. Without the presence of azotized compounds, no blood nor muscle can be formed. Hence the quantity of these compounds in plants, along with phosphates which form bone, indicates their blood-forming or sanguigenous value. Nitrogen is known to us as a gas forming 79 volumes per cent. of the atmosphere, and moderating the effect of oxygen on all oxidable bodies. Like hydrogen, it is sparingly soluble in water. It enters into combination with hydrogen, and forms ammonia, composed of 1 equivalent of nitrogen and 3 of hydrogen (NH₃). Ammonia is given off during the decay of animal tissues, in the form of a pungent vapour, which is readily absorbed by water, and also in combination with other substances, such as carbonic acid and sulphuretted hydrogen. The nitrogen of the air may also, as some think, combine with hydrogen in the soil, and form ammonia. The presence of ammonia in the atmosphere was determined by Saussure in 1806. Ville has recently stated that the nitrogen of the air is assimilated by plants, but his observations have not been confirmed.

In order that azotized matter may be formed, plants must have a supply, not only of nitrogen, but also of sulphur and phosphates. The two latter are derived from the soil, in the form of soluble compounds of sulphuric and phosphoric acids, while the former is derived, according to Liebig, not from the nitrogen of the air, but from the ammonia diffused through it. This ammonia constitutes only 1-10,000th of the bulk of the air at the utmost; it is usually much less. This, however, has been shown to be sufficient for the supply of nitrogen to plants. Ammonia is returned to the air during the processes of putrefaction which go on in dead animals and plants, as well as in the excreta of the former, such as the urine. It is also yielded by transpiration. Thus ammonia is continually sent into the atmosphere, and by the constant movement of the air the supply is diffused. Ammonia is also absorbed by the soil, and may thus be rendered available for the use of plants. It is known also that in some instances volcanic action gives rise to the formation of ammonia. Daubeny believes that the ammonia, as well as the carbonic acid which formed the food of the first plants, was produced, not by processes of animal decay, but by such as were proceeding within the globe prior to the creation of living beings, and that the disengagement of both these compounds has been going on slowly and continuously from the earliest period to the present time. Others think that part of the nitrogen of plants is derived from nitric acid and nitrates, and this view is gaining ground. Nitric acid is produced during thunder storms, and in the rain which falls during these storms; this acid has been detected in small quantities. The nitric acid in these instances probably proceeds not only from a combination between the nitrogen and oxygen of the air, but also from a combination between the ammonia and oxygen. The minute quantity of nitric acid and nitrates in some springs may also supply nitrogen. The nitric acid in these instances appears to proceed from the decay of animal matter, and from the oxidation of ammonia.

All the azotized matters to which we have alluded are formed by a process of deoxidation from carbonic acid (CO₂), water (HO), hydrated ammonia (NH₄HO), nitric acid (NO₃), and sulphuric acid (SO₄). They all contain much less oxygen than is necessary to convert their hydrogen into water, their carbon into carbonic acid, and their sulphur into sulphuric acid. They are never found alone in plants, but generally two of them together. They cannot exist without the presence of phosphates. Hence the ashes of plants are in part derived from the sanguigenous (blood-producing) matters, such as albumen and fibrine, which enter along with cellulose into the composition of the cell-walls.

2. Inorganic Constituents of Plants.

The terrestrial or telluric food of plants, as it is termed, consists chiefly of certain inorganic matters, the amount of which is ascertained by the ash left after burning. While the organic constituents of plants are destroyed by a high temperature, and undergo decay under the agency of moisture and warmth, the inorganic constituents are incombustible, and do not undergo the putrefactive process. There are at least 12 inorganic elements which enter into the composition of plants:

- Sulphur, S, as Sulphuric acid, SO₄. - Phosphorus, P, as Phosphoric acid, PO₄. - Silicium, Si, as Silicic acid, SiO₄. - Calcium, Ca, as Lime, CaO. - Magnesium, Mg, as Magnesia, MgO. - Potassium, K, as Potassa, KO. - Sodium, Na, as Soda, NaO. - Chlorine, Cl, in combination with metals. - Iodine, I, do. - Fluorine, F, do. - Iron, Fe, in combination with oxygen, Fe₂O₃. - Manganese, Mn, do.

Alumina (Al₂O₃), the sesquioxide of Aluminium, which has been noticed by some authors as another inorganic constituent of plants, seems to be an accidental ingredient, being sometimes present, and at other times absent. Mr Stevenson Macadam has recently obtained indications of the presence of Bromine (Br) in plants.

The quantity of inorganic matter in plants is small when compared with the organic constituents. It is nevertheless essential to the life and vigour of plants. The cell-walls cannot be formed without inorganic matters, and some of them enter into the composition of the azotized substances formed by plants. Thus sulphur and salts of phosphoric acid are necessary for the formation of albumen, fibrine, and caseine. In some rare instances of plants forming mould, no ash has been detected.

The quantity of ash left by 100 parts of the following plants is thus given by Johnston:

| Plant | Ash % | |-------------|-------| | Wheat | 3 | | Barley | 2 | | Oats | 1 | | Rye | 1 | | Indian Corn | 1 | | Field Peas | 1 |

Thus the quantity of inorganic matter in the same weight of different crops varies. It will be seen, for instance, that the grain of barley yields more ash than wheat or rye. The quantity of inorganic matter also in different parts of the same plant varies, as seen in the grain and straw of cereal grains, and the wood and leaves of trees.

The following comparative results are given by Johnston of experiments made by different chemists regarding the more important inorganic constituent in 100 parts of some of the cultivated plants and trees:

| Names of Plants | Potash | Soda | Lime | Magnesia | Silica | Ash % | |-----------------|--------|------|------|----------|--------|-------| | Wheat | 3 | 12 | 59 | 0.25 | 1 | 3 | | Barley | 2 | 7 | 39 | 0.10 | 27 | 2 | | Oats | 6 | 10 | 44 | 11 | 3 | 6 | | Rye | 5 | 10 | 50 | 1 | 0.4 | 5 | | Maize | 1 | 16 | 45 | 3 | 1 | 1 | | Rice | 1 | 12 | 53 | 0 | 3 | 1 | | Beans | 6 | 8 | 38 | 1 | 1 | 6 | | Peas | 5 | 8 | 33 | 4 | 0.51 | 5 | | Wheat Straw | 7 | 4 | 3 | 6 | 65 | 7 | | Barley do. | 10 | 3 | 3 | 2 | 71 | 10 | | Oat do. | 8 | 4 | 3 | 3 | 48 | 8 | | Rye do. | 9 | 2 | 4 | 1 | 65 | 9 | | Maize do. | 8 | 7 | 17 | 0 | 28 | 8 | | Rice do. | 6 | 5 | 1 | 4 | 74 | 6 | | Bean do. | 20 | 7 | 7 | 1 | 7 | 20 | | Pea do. | 5 | 7 | 5 | 7 | 20 | 5 | | Red Clover | 33 | 8 | 8 | 3 | 7 | 33 | | Potatoes | 57 | 2 | 5 | 13 | 14 | 57 | | Turnips | 47 | 5 | 8 | 14 | 8 | 47 | | Beet | 9 | 5 | 2 | 10 | 10 | 9 | | Cabbage | 21 | 6 | 12 | 22 | 0.74 | 21 | | Potato Haulm | 17 | 7 | 8 | 7 | 4 | 17 | | Turnip do. | 23 | 3 | 9 | 13 | 1 | 23 | | Elm Bark | 72 | 3 | 1.7 | 0.6 | 8 | 72 | | Elm Wood | 47 | 7 | 3 | 1.2 | 3 | 47 | | Lime Bark | 60 | 8 | 4 | 0.7 | 2 | 60 | | Lime Wood | 29 | 4 | 4 | 5 | 5 | 29 | | Cherry Bark | 44 | 5 | 3 | 0.8 | 21 | 44 | | Cherry Wood | 35 | 11 | 9 | 4 | 5 | 35 | | Scotch Fir Seeds| 23 | 15 | 45 | ... | 10 | 23 |

From this table it will be seen that the quantities of different mineral matters vary in different plants, and in different parts of the same plant. Silica is present in large quantity in the stems of grasses, while it forms usually a small proportion of grains, leguminous plants, and succulent roots. Phosphoric acid is more abundant in the grain of cereal plants than in the straw; it exists also in considerable quantity in nutritive seeds and in potatoes and turnips. Lime abounds in the stems of beans and peas, in clover, and in the bark and wood of trees; while it exists in small quantity in the cereal plants and grasses. The proportion of lime in the bark of trees is greater than in their wood. Potash and soda enter more largely into the composition of green crops than into that of white crops; they are also more abundant in the wood than in the bark of trees.

Most plants contain more or less of potash and soda in their composition. The former prevails in inland plants, Botany. the latter in maritime and marine plants. Some succulent sea-shore plants, such as Salsola Kali, and Salicornia herbacea, yield a large quantity of soda in their ashes. Some species of plants which grow both in maritime and inland situations contain a preponderance of soda in the former locality, and of potash in the latter. This is the case with the common Sea-pink (Armeria maritima), Scurvy-grass (Cochlearia officinalis), and sea-side Plantain (Plantago maritima).

The presence of lime has been detected in almost all plants. It is an abundant ingredient of the soil, and is often associated with magnesia. In combination with phosphoric acid, it is an essential ingredient of the nitrogenous matter of cereal grains, and of many other cultivated plants. As sulphate it occurs largely in some of the Charas and Medicks. It sometimes appears as an incrustation on the cells of plants, in the form of carbonate. This is seen in species of the genus Chara (especially Chara hispida) which grow in ponds. In the interior of cells, salts of lime are often seen in a crystalline form, constituting Raphides. Oxalate of lime crystals occur in Rhubarb root; in the best Turkey Rhubarb they constitute 35 per cent. of the dried tissue, in East India Rhubarb 25 per cent., and in English Rhubarb 10 per cent. In some of the Cactus tribe, especially in old specimens of Polocereus senilis, these crystals are so numerous as to render the stem brittle. Crystals of phosphate, sulphate, carbonate, tartrate, malate, and citrate of lime also occur in the cells of plants.

The presence of silica (SiO₂) in plants give solidity and firmness to their stems. The quantity in some plants, such as Equisetum, is very large. In these plants, as well as in grasses, the silica exists in the form of small plates, grains, or needles, as may be shown by the action of sulphuric acid. In the Bamboo (Bambusa arundinacea, and other species) the quantity of silica at the joints is frequently very large, and may be collected in masses, to which the name of Tabasheer is given. In the Diatomaceae, belonging to the lowest tribe of Algae, the cells have a siliceous covering, which enables them to retain their form, even after being acted on by strong acids.

Iodine was considered formerly as an ingredient of maritime and marine plants only, but it has been recently detected in fresh-water plants, as well as in many ordinary land plants, by Chatin and by Macadam. The presence of fluorine in plants was first detected by Will of Giessen, and his observations have been confirmed and greatly extended by Dr George Wilson. It occurs in small quantity in plants, and it is often associated with silica, from which it is separated with great difficulty. Plants growing on the sea-shore, such as Sea-pink and Scurvy-grass, have been proved by Voelcker to contain fluorine. The test for the presence of fluorine is the etching which hydrofluoric acid produces on glass.

Plants derive all their inorganic materials from the soil, and it is consequently of importance to determine the composition of the latter. Some plants, however, are enabled to grow without coming into contact with the soil. Thus in the Botanic Garden of Edinburgh, Urostigma elasticum, Ardisia crenulata, Agave (Littrea) gemmipara, Billbergia nutansalis, and Phoenix farinifera, have continued to grow for nearly four years suspended in the air, and merely moistened by common water allowed to come into contact with the roots by the capillary action of a worsted thread. Urostigma australe has grown suspended in the air for nearly twenty-five years. The plants have produced leaves and some of them flowers. They derive their organic nourishment from the air, and the quantity of inorganic matter in the water appears to be sufficient to supply their wants in that respect for a long period. Air-plants or Epiphytes, such as Tillandsias and Orchids, are usually attached to other plants, from the decaying bark of which they may derive inorganic matter. In hothouses these Epiphytes have also a quantity of moss round their roots, which is another source of inorganic matter. Lichens seem to have the power, in many cases, of acting upon hard rocks, and deriving from them inorganic matters. Mulder states that mould plants found on the surface of saccharine and gummy solutions, as well as in vinegar and other organic substances, consist of cellulose and nitrogenous compounds, without any inorganic matter. These plants, according to him, leave no ash on being burnt.

3. Composition and Properties of Soils as supplying Food for Plants.

Having considered the various organic and inorganic matters which enter into the composition of plants and of vegetable products, and having noticed the chief sources whence plants derive their carbon, oxygen, hydrogen, and nitrogen, we shall now examine generally the nature of the soil, as the source whence the mineral or inorganic matters required for vegetable growth and nutrition are derived. We have seen that the atmosphere, with its carbonic acid, water, nitric acid, and ammonia, is capable of supplying the organic constituents of vegetables. At the same time we have found that sulphur and phosphates enter into the composition of some of the most important sanguigenous (blood-producing) products. To the salts of sulphuric and phosphoric acid in the soil, we must look, therefore, for the means of enabling plants to assimilate their organic products. While we allow that the atmosphere is the great reservoir whence the organic elements are derived, still we cannot consider it as the exclusive source. It is probable that some of the carbon, oxygen, hydrogen, and nitrogen of plants may be supplied by the soil, and at all events we have seen that these elements cannot be combined in the form of albumen, fibrine, and caseine, without certain mineral matters of telluric origin.

The atmospheric supply of food is pretty uniform, and is not under the control of man. It is to the terrestrial (telluric) supply he must look as that which can be increased and modified by his efforts. The horticulturist and farmer direct their attention to the soil, and by alterations in its composition endeavour to effect changes in the plants which they cultivate. It is therefore of importance to ascertain the mechanical nature and chemical composition of the soil.

The following are the substances which enter generally into the composition of soils—Silica, clay, lime, and humus or vegetable mould. According to the preponderance of one or other of these ingredients, soils are usually classified.

The presence of sand and gravel in soils renders them loose and friable. Such soils part with moisture easily, and are usually dry. When the proportion of sand is very large, the soils are barren and unproductive. The addition of clay, chalk, and marl, is useful in rendering sandy soils more tenacious. As silica enters more or less into the composition of plants, it must be taken up from the soil by the roots of plants. In order that this absorption may take place, the silica must be dissolved in water. In its uncombined condition it is insoluble, but by combining with alkalies such as potash, it forms soluble silicates, which enter the cells of plants.

Clayey soils contain a large quantity of insoluble silicates, and of alumina, which does not appear to be an essential constituent of plants, although it is occasionally found as an accidental addition to their tissues. The presence of clay has a tendency to make soils stiff and firm, so that they can retain the roots of plants and give them support. Clay soils are usually moist, impervious, and cold. Heavy clay land is improved by draining, by burning, and by mixing chalk and sand with it. Way finds that clay in the soil removes various important matters from the manures put upon Calcereous soils contain upwards of 20 per cent. of lime. This substance exists abundantly in the vegetable juices, and hence its presence is required in all productive soils. Calcereous soils exhibit different physical characters according to the proportion of lime, clay, silica, &c., which enter into their composition. The addition of lime to soils is often highly beneficial, by destroying noxious weeds, and by preventing disease in crops. Lime, in combination with phosphoric acid, is a valuable ingredient of soils. Sulphate of lime or gypsum seems to be useful, not merely in supplying sulphuric acid and lime, but also in fixing ammonia. In marly soils lime exists in proportions varying from 5 to 20 per cent. In loamy soils lime is in smaller quantity, and the clay does not exceed 50 per cent.

Humus soils contain much vegetable mould. This is insoluble, and cannot be taken up by plants. By the action of air and moisture, &c., the humus is decomposed, and various acids are formed, which seem to be capable of supplying carbon to plants. Vegetable moulds also absorb gases, such as ammonia, in large quantity, and thus supply nutritive matter to plants.

The alkalies, potash and soda, are important constituents of plants, and they exist in greater or less quantity in soils. They enter into the composition of minerals, such as felspar. They are taken up by plants in combination with acids. They render silica soluble, and they are essential to the development of acids, such as oxalic, citric, and malic, with which they are found in combination. They appear to replace each other in certain circumstances. In many fertile soils magnesia exists in combination with carbonic acid, phosphoric acid, and lime. In flax there is a large proportion of magnesia. In its caustic state magnesia is injurious to vegetation.

Iron has been detected in greater or less quantity in the ashes of all plants. It exists in the soil in combination with oxygen, sulphur, and carbon. The oxides of iron are found, more or less, in all soils, and the peroxide, which is the most abundant, imparts that reddish colour so often observed on the earth's surface. The protoxide of iron is of less value than the peroxide for vegetation, as it readily forms salts which are injurious to plants. It frequently abstracts oxygen from the soil, and becomes fully oxidized. Manganese exists sparingly in plants, and it is found in the soil combined with peroxide of iron. The presence of iodine in plants has been fully recognised by many observers. Chatin believes that there is an appreciable quantity of iodine in the atmosphere, in rain water, and in the soil, varying in different districts, and that the relative amount of iodine, in any one locality, determines, to a great extent, the presence or absence of certain diseases, such as goitre and cretinism. Mr Stevenson Macadam, from a very accurate series of experiments, has been led to the conclusion, that air and rain water do not contain iodine, at least in such quantity as to be detected by the most delicate tests. It is probable that it is derived from soluble iodides in the soil. Iodine is said to exist in coal and in the waters of the globe. The waters from igneous rocks, and from the rocks of the coal formation, are said to contain a considerable quantity of iodine. It is found in combination with sulphur, the ores of iron and manganese, and the sulphuret of mercury.

The sources of the Fluorine found in plants, Wilson regards as pre-eminently two—Simple fluorides such as that of calcium, which are soluble in water, and through this medium are carried into the tissues of plants; and Compounds of fluorides with other salts, of which the most important is probably the combination of phosphate of lime with fluoride of calcium. This occurs in the mineral kingdom in apatite and phosphorite, and in the animal kingdom in bones, shells, and conchs, as well as in blood, milk, and other fluids. Fluorides are much more widely distributed than is generally imagined. They exist in well, river, and sea water.

The productiveness of soils is very various. Some are entirely barren, such as quartz rock. This kind of soil is seen in many mountainous districts in which the bare quartz rock continues to show itself without any vegetable covering whatever. Others contain materials fitted for nourishment, but not available until they are disintegrated. This is the case with many granitic rocks containing valuable nutritive matter which can only be taken up by plants after the rocks have been pulverized by the action of the weather. Some hard granites which are not thus acted upon are barren. Some soils are unproductive on account of their physical characters, such as very stiff clays; others are so on account of being too loose and sandy; while others, from excess of water, are too moist, and require draining before they can be productive. The presence of substances in an unavailable form is the most common cause of sterility in soils. Barren felspar soils may be rendered fertile—by exposure to the air, or in other words, by lying fallow; by frequent ploughing and turning up; by the use of quicklime, which acts by accelerating the decomposition of felspar and clay, and separating the silica and potash from the former; by burning or calcination which acts in the same way as lime. Thus fallow, ploughing, liming, and burning act in the same way on barren felspar soils, by causing decomposition, and separating the materials required for the nourishment of plants. They all promote the solubility of different parts of the soil. Below the ordinary soil there occurs what is called the subsoil, in which there is less organic matter than on the surface. Into this soil many soluble matters are carried down by rains. The effect of subsoil and trench-ploughing is to bring up these matters and render them available for the use of plants. The beneficial results of this kind of ploughing will depend upon the composition of the subsoil.

4. Rotation of Crops and Application of Manures.

Some plants require certain inorganic matters in larger quantity than others, and it is upon the knowledge of this that the rotation of crops is founded. The soil is constantly losing inorganic matters. By continuing to cultivate the same crop, we deprive the soil, to the depth to which the roots extend, of certain materials, while others are left nearly untouched; but by alternation of crops the latter may be made available for the purposes of growth. Farmers on this account have different crops succeeding each other in the same field. Wheat, barley, and oats are described as silica plants; peas, beans, and clover as lime plants; turnips and potatoes as potash plants. These crops, from the difference in their predominant inorganic ingredients, are made to alternate with each other. In some virgin soils, rich in phosphates and other inorganic matters, the same plants may be cultivated successfully for many years.

There is often a great quantity of fertilizing matter in the soil, but not in a condition immediately available for the growth of plants. Hence, in some cases where the crop is deficient, there are valuable materials still in the soil unassimilated. Thus phosphates exist often potentially in a dormant state in the soil in great abundance, but it is not until they have been brought into a soluble form that they are of any use as the food of plants. It is of importance for an agriculturist to discover the dormant inorganic materials, and to adopt means of rendering them available. Allowing the ground to lie fallow, and stirring and pulverizing of it, are methods by which air and moisture are admitted, and time is allowed for the decomposition of the materials, which are thus rendered available for plants. The materials of which plants are composed, and which are all withdrawn from the unorganized world, are given back to the air and soil again by the disintegration of the living structures of which they have formed a part. If plants were not used for food, they would by their decay restore all that they had taken away for the purposes of growth. But as they contribute to the nourishment of man and animals, it follows that a portion of vegetable matter is constantly removed in order to build up the animal structures. This portion must be again supplied in order that the plant may be nourished. This is the principle of the application of manures. The farmer and horticulturist add to the soil what has been removed from it by crops. In order to do this properly, there must be a knowledge of the composition of the plant, of the soil, and of the manure; and hence the importance of accurate chemical analyses. In addition to this, attention must be directed to the functions of plants, and to the mode in which they take up nourishment; and the materials of growth must be supplied in such a way as to be made available for the purposes of plant-life.

The object of manuring is to improve the properties of the soil, and to supply what has been taken from it by crops which have been used for the food of man and animals. We may either supply the whole or some portion of the vegetable constituents in a soluble state, or we may add to the soil something which will decompose and act on its insoluble ingredients, so as to render them fit for the use of plants. Natural manures, such as those of the farm-yard, are excellent, because they restore to the land nearly all the substances which have been taken from it. Other manures supply one or two ingredients only. The exposure of the soil to the influence of the weather tends to make up for loss, by causing the decomposition of substances previously unfit for vegetable nutrition. Fallow then acts, in a certain degree, in restoring the fertility of the soil, but it will not give us all that is required, and, moreover, involves loss of time and money.

In the case of cultivated plants, those manures are considered the most valuable which furnish the materials necessary for forming the azotized compounds required for the sanguigenous food of man and animals. Hence the importance of manures containing ammonia and phosphates, substances which do not usually exist abundantly in the soil, and which are annually required in large quantity by crops. It has been found by comparative experiments that the quantity of gluten in wheat and other cereal grains is increased by the use of ammoniacal and phosphatic manures. The sewerage of towns, in this point of view, is one of the most valuable manures, and it is to be regretted that so little is done to save it for the purposes of the farmer and horticulturist.

The soil has a great power of absorbing ammonia, and supplies it gradually to the roots of plants in a state fit for their nutrition. The vigour of plants is much increased by the judicious application of ammonia either in the soil or in the air. It is essential that ammonia should be supplied in moderate quantity at a time, and at the proper season. It requires also the presence of phosphates, in order that its full effect may be secured in the production of nitrogenous matter. Some manures give off ammonia in large quantity by a process of fermentation; and in order to prevent the loss thus occasioned, it is frequently necessary to add sulphuric acid or sulphate of lime, so as to procure a non-volatile sulphate of the alkali.

Manures may be divided into—1. Farm-yard manure, containing all the ingredients required for a crop. This, when applied to the soil, is slowly decomposed, and its effects extend over several years, so that it exerts a beneficial influence upon all the crops of a rotation. It may be called in general a slowly-acting manure. 2. Special manures, composed of ingredients which are intended for the special benefit of the crop to which they are applied, while comparatively little effect is expected to be produced on those that succeed it. These may be called rapidly-acting manures. The first is of importance for cereals which are slow-growing plants; the second are valuable for green crops, which of all others require the greatest quantity of nourishment in a given time. While ammonia may be supplied by both, still, in the former it is slowly produced by a gradual combination between nitrogen and hydrogen, while in the latter it is ready formed, and capable of being at once used by the plant.

Farm-yard manure consists of complex animal and vegetable compounds, which by free exposure to the air undergo a kind of fermentation, so as to be converted into other substances, of which carbonic acid and ammonia are the most important. This fermentation is promoted by moistening and turning over the manure, in order to permit the free access of air. It may be applied in a solid or in a more or less fluid state. The term liquid manuring is properly given to the use made of the urine of cattle, containing a large amount of urea, which, by decomposition, becomes carbonate of ammonia. Of late, however, this has been mixed with other matters from the farm-yard, as well as with carbonaceous and peaty substances, and the whole has been pumped over the field in the form of a fluid containing solid ingredients suspended in it. This kind of fluid manure is more beneficial than liquid manure properly so called.

Among Special manures there are some which supply ammonia and phosphates either separately or united, others furnish acids or bases, such as Sulphuric acid, Nitric acid, Potash, Soda, Lime, &c. The liquor of gas works and soot owe their manurial value principally to ammonia. Bones are prized on account of the phosphate of lime in their composition, which amounts in general to about 50 per cent. In place of using bone-dust, which acts slowly, from the insoluble nature of the phosphate of lime, farmers are in the habit of mixing bones with sulphuric acid, and thus getting a soluble compound of phosphoric acid and lime (super-phosphate), which, when dissolved in water, is easily taken up by the roots of plants. The addition of sulphuric acid also acts beneficially in supplying sulphur for the azotized compounds. One of the most important special manures is Guano, or the dung of sea-fowl, which has accumulated for centuries in some parts of the coast of South America and Africa, and now forms enormous deposits. Its value depends partly on ammoniacal salts and partly on phosphates. Some guanos, as Peruvian, Anagamos, and Bolivian, are rich in ammonia; while others, as Patagonian and Saldanha Bay, are rich in phosphates.

Various other special manures have been recommended, containing one or two of the inorganic constituents of plants. Nitrates and Carbonates of Potash and Soda appear to act by furnishing alkaline matter as well as nitrogen and carbon. Sea salt (Chloride of sodium) is considered by Mr Way as beneficial both to white and green crops. He thinks that it probably acts on the silicates of lime present in the soil setting the lime free, and acting on the silica so as to render it fit for the purposes of vegetable life. In the case of cultivated plants which naturally grow near the sea, such as Sea-kale, Asparagus, Cabbage and its varieties, salt may be expected to be useful. Lime acts beneficially as a manure in the case of some plants, prejudicially as regards others. Occasionally a green crop is grown with the view of being afterwards ploughed into the soil, and of supplying, during its decomposition, materials which had been taken up by its roots from a considerable depth in the soil. This is called green manuring. Sea-weeds are also used as manure.

II. PHYSIOLOGY OF THE DESCENDING AXIS OR ROOT.

The Root is the descending system of the plant, and is the organ directly concerned in the absorption of nourishment from the soil. In its earliest state it is a cellular prolongation from an axis which is common to it and the stem. In cellular plants, the root consists also of cells. Root-cells are developed in a downward direction, and the fibrils spread through the soil, so as to absorb nutriment and to fix the plant firmly. The additions to roots are made at their extremities, and there it is that the chief absorbing cells are situated, constituting what have been called Spongioles (Fig. 62). Connected with young roots there are hairs or cellular prolongations from the epidermis, which also absorb fluid food. These hairs die early with the epidermis from which they sprung; the root then becomes covered with a corky layer, while its extremity continues to grow and send out fresh hairs. Any injury done to the absorbing extremity interferes more or less with the proper nutrition of the plant.

As plants are fixed to a spot, their food must be always within reach, and it is requisite that the roots should have the power of spreading, so as to secure renewed supplies of nutriment. A beautiful provision is made for this by the elongation of the roots taking place at their extremities, so that their advancing points are enabled easily to accommodate themselves to the nature of the soil in which the plant grows. If roots had increased by additions throughout their whole extent in the same way as stems, they would in many instances, when meeting with an impenetrable soil, have been twisted in such a way as to unfit them for the free transmission of fluid. But by the mode of lengthening at the point, they insinuate themselves easily into the yielding part of the soil, and when obstacles are presented to their progress, they wind round about them until they reach a less resisting medium. They are thus also enabled to move from one part of the soil to another, according as the nourishment is exhausted.

The root, in its growth, keeps pace with the development of the stem and its branches. As the stem shoots upwards and develops its leaves, from which water is constantly transpired, the roots continue to spread, and to renew the delicate cells and fibrils which absorb the fluid required to compensate for that lost by evaporation, or consumed in growth. There is a constant relation between the horizontal extension of the branches and the lateral spreading of the roots. If the roots are not allowed to extend freely, they exhaust the soil around them, and are prevented from receiving a sufficient supply of food. The plants in such a case, deprived of their proper means of support, become stunted and deformed in their appearance.

If we wish trees to be firmly rooted, we must allow the branches to spread freely. When they are so planted that the branches and leaves of contiguous trees do not interfere with each other, and thus all parts are exposed to air and light equally, the roots spread vigorously and extensively, so as to fix the plants in the soil, and to draw up copious supplies of nourishment. But in crowded plantations, where the branches are not allowed freedom of growth and exposure, and the leaf-buds are consequently either arrested or feebly developed, the roots, also, are of necessity injured. They do not spread, and the trees are liable to be blown over by the wind; they exhaust the soil in their vicinity, circumscribed by the roots of the trees around; their functions become languid, and thus they react on the stem and branches, so that the additions to the wood are small, and the timber is of inferior quality. The spreading of roots in favourable circumstances is often remarkable. Thus, the roots of trees and other plants, when they reach reservoirs of water, as wells or drains, are found to increase very rapidly, and extend to a great length. Drains are sometimes completely blocked up by roots, in consequence of a single fibril entering at a small crevice, and then expanding into a large fibrous mass.

Roots, by depriving the soil of certain nourishing matters, render it unfit for the growth of the same species of plant, although it may still be able to contribute to the growth of other species. This is the principle of the rotation of crops, to which allusion has already been made. This exhaustion of the soil affords an explanation of the phenomenon called fairy rings, consisting of circles of dark green grass seen in old pastures. These have been traced to the successive generations of certain fungi spreading from a central point, exhausting the soil at first, and afterwards by their decay, causing a luxuriant crop of grass.

The spongioles and cellular hairs of the fibrils of roots absorb fluid food, and by diffusion communicate the matter absorbed to the neighbouring cells, and these in turn send it through their membranes upwards into the stem. Senebier proved by experiments that the absorption takes place principally by the cells at the points of the roots. After the corky layer is formed, the cells seem to have less power of taking up fluids through their walls. The imbibition by the roots may be traced in part to the process of endosmosis already described, and in part to certain vital actions going on in the cells. By virtue of the chemical composition of its cell-walls and juices, and by vital affinity, a plant absorbs one substance more quickly than another, and consequently in a given time more of one than of another.

That the roots of plants have a certain power of selection was proved by the experiments of Saussure. He immersed the roots of plants in water, containing in solution an equal weight of two different salts, and when the plants had absorbed half the water, he took them out and evaporated the remaining water, so as to determine how much of the salts remained. This of course indicated what the plants had taken up. The salts were not absorbed in equal quantities. This difference in the proportion of salts taken up was only observable so long as the roots were entire; for when their extremities were cut off the different saline matters were taken up in the same proportion. The absorption of saline matters by the roots of plants varies in individual plants of the same species, as well as in plants belonging to different species. The absorption, according to the observations of Saussure, does not seem to have reference to the value of the substances as nutriment. Substances are taken up which prove injurious to plants. Trinchinetti placed different species of plants in mixtures of two salts—nitre and common salt—which do not decompose each other, and he found that one plant absorbed the one, and another plant the other salt, in preference.

Besides absorption, it has also been stated that excretion takes place by roots, or in other words, that matters which have been taken up from the soil, and which are not required for the use of the plant, are again returned by the roots. This subject was investigated by Macaire, who looked upon these excretions as injurious to plants. The recent observations of Gyde and others, however, lead to the belief that the excretions of roots are in small quantity, and that they do not possess the deleterious properties which were attributed to them. It is probable that the substances given off by roots may be referred to a process of exosmosis.

Some roots which do not ramify have reservoirs of nutriment stored up in the form of nodulose or tubercular masses. This occurs in terrestrial Orchids, and in Dahlias. In the case of Spondias tuberosa, the tubercles of the roots contain a large quantity of watery fluid. In climbing plants, such as Ivy, the root-like processes by which they are attached to trees or walls seem to be means of support rather than organs of nutrition. Aerial roots take up nourishment from the atmosphere chiefly. This is the case with the roots of many Epiphytic Orchids, and in consequence of not being in a resisting medium like the soil, the elongation in them seems not to be confined to the extremities, as Botany, shown by the experiments of Lindley on Vanilla and Aerides cornutum. The roots of these Epiphytes or air-plants may derive some nourishment from the decomposition of the bark of the trees on which they grow, as well as from the decay of mosses, lichens, &c., which accumulate around them; but their principal nutriment appears to be supplied by the water, carbonic acid, and ammonia of the air. Roots, when exposed to the air, lose their fibrils, and take on the functions of stems, so as to produce leaf-buds.

Some plants, in place of sending their roots into the soil, or extending them into the air, have the power of attaching themselves to other plants in such a way as to prey upon their juices. These are called Parasites. Some of them have green leaves, such as the Mistletoe; others have only white or brown scales, as the Scalewort and Broom-rape. In the former, the juices, after being taken up by the plant, are altered in the leaves by exposure to air and light. Some of these are root-parasites, in other words, become attached to the roots of other plants; as Broom-rape, Eyebright, Bastard Toad-flax, and Cow-wheat; others are stem parasites, growing by attachment to the stems of other plants; as the Mistletoe, Myzodendron, Rafflesia, and Dodder.* All of them send cellular prolongations more or less deeply into the tissue of the plants on which they feed, and by means of these, which act as roots, they derive nutriment. They often cause great injury to the plants on which they grow.

III.—PHYSIOLOGY OF THE ASCENDING AXIS OR STEM.

The stem produces buds which are developed as branches, leaves, or flowers. It conveys fluids in various directions, and allows the organs of plants to be exposed to the influence of air and light. In the case of subterranean stems, the leafy and flowering branches are sent upwards into the air; and they perform the functions of aerial stems. Herbaceous stems carry on their functions for one year, or for a limited period, while those of a woody nature continue to perform their functions for many years. While the former attain a moderate size, and perish after a brief period of existence, the latter are permanent, and frequently, as in the case of trees, acquire a great height and diameter. Herbaceous axes occasionally attain a large size, as may be seen in Bananas. Many cone-bearing trees, as Pines, Spruces, Larches, Araucarias, Sequoia, and Wellingtonia, have stems varying from 100 to 300 or more feet in height. Other dicotyledonous forest trees in Britain sometimes attain the height of 120 feet; while on the Continent and in America, they are sometimes 150 feet high. Monocotyledonous stems, such as those of Palms, are usually unbranched, and their height is sometimes 150 or even 180 feet. The Cable Palm runs among the trees of the forest to the length of 500 feet. Acotyledonous stems, as those of species of Alsophila, Dicksonia, and other Tree-ferns, attain a height of 50 or 60 feet. Some cellular stems also attain a large size. Dr Hooker mentions a sea-weed—Lessonia fuscescens—with a trunk 5–10 feet long, and as thick as the human thigh. Stems often attain a great thickness. The stem of the Dragon-tree of Orotava is 70 feet in circumference; that of the Baobab has a circumference of 90 feet; some Cedars of Lebanon at the present day have a girth of 40 feet. Chestnut trees have occasionally a circumference of 60 feet, and trees of the South American forests are mentioned by Martius with a girth of 84 feet at the base of the trunk. While some Palms, such as Kunthia montana and Oreodoxa frigida, have slender reed-like stems; others, such as Cocos butyracea and Jubaea spectabilis, have trunks which are three or even five feet in diameter.

By means of terminal and lateral buds, stems increase in height and diameter. In their earliest state they are composed of cellular tissue, in the midst of which there is developed vascular tissue, which is arranged in different ways, as already described. The cellular tissue of the young dicotyledonous stem is early separated into two portions—a medullary or inner, and a cortical or outer—by the formation of vascular and woody bundles, which increase in concentric zones. In its young state, the pith is succulent and seems to be a reservoir of nourishment for the embryo plant during its early growth. The sheath surrounding the pith contains numerous spiral vessels, which extend upwards and outwards to the leaves. In ordinary circumstances these vessels contain air. The outer cellular portion of the stem constitutes the bark, which protects the other tissues, and often contains secretions, such as gums, resins, and alkaloids. When the bark is green, it seems to exercise the same functions as leaves. It is united to the pith by medullary rays which give a character to the wood. The cells and vessels of the stem are concerned in the circulation of sap, as will be afterwards noticed, and the woody tubes, when fully formed, give stability and durability to the trunk.

Between the pith and bark, as well as at the extremities of the buds and roots, there exist cambium cells, which, according to Schacht, form the first stage of the vascular bundles, and give origin to the proper parenchyma or nourishing tissue. A cylindrical layer of this cambium or organizing tissue is distributed in all the most perfect plants, so as to divide the parenchyma into pith and bark, as well upwards in the stem, as downwards in the root. In Dicotyledons, this cylindrical layer, called by Schacht the thickening zone, is active as long as life remains. It is by means of it that the stem enlarges—the cells of the tissue forming, toward the interior, new wood, and, towards the exterior, new bark.

In Monocotyledons and the higher Cryptogams, the thickening zone—in other words, the cylindrical layer of organizing tissue—continues active only for a short period of time, and hence these plants do not enlarge beyond a certain point; and at length they grow only in one direction—namely, in height. This thickening layer of cambium, while it adds to the size of the stem of Monocotyledons, causes the increase of the vascular bundles. After a certain period, however, this zone becomes woody, and then the vascular bundles only grow at their extremity, by means of unchanged cambium cells which are in immediate connection with the bundles. This cambium of the vascular bundles is essential to them, and gives them their character. In Monocotyledons it is situated in the centre of the bundles, and is surrounded by spiral, pitted, or woody vessels; in Cryptogams it surrounds the vascular bundles. The vascular bundles in both these classes of plants are limited, and they can only increase laterally by ramifying, as in Dracaena and some Tree-ferns.

The cambium appears to be the immediate agent in the development of new tissues. The origin of the cambium cells, and the mode in which the wood of trees is formed, as well as the influence exerted by the leaves and green parts of plants, have long been subjects of dispute among physiologists. Grew and Malpighi thought that the new woody layers were formed by the bark, while Hales maintained that they were formed from the previously existing wood. Dr Hope loosened the bark of trees, and found new layers of albumen formed on its inside. Duhamel put plates of silver between the woody and cortical layers, and found the new formation on the outside of the plates; he also removed a portion of the bark of a plum-tree, and replaced it with a similar portion of a peach-tree, and after union had taken place, he ascertained that at the point of junction a thin layer of wood had been formed by the peach bud, and none by the wood of the plum. Hence these experimenters concluded that the new wood was produced by the bark. De Candolle, as the result of his observations, maintained that both the bark and the wood were concerned in the formation of woody matter. All appear to agree in looking upon the cambium layer as concerned in the development of the wood.

We have seen that recent authors have ascertained more fully the nature of cambium, and that they consider it in the light of active formative tissue, developing cells and vessels in an upward and downward direction. Some adopt the view that there are in reality two systems in plants, an ascending and a descending one; and that what takes place in the sprouting of the embryo continues to be manifested during the life of the plant. This view, variously modified, was adopted by De la Hire in 1708, was supported by Darwin and Knight, and was particularly espoused by Aubert du Petit-Thouars in 1806, and subsequently by Gaudichaud and others.

According to Petit-Thouars and Gaudichaud, we see in the embryo a radicular and a caulinary portion, the one having a tendency to ascend, the other a tendency to descend. In both of these systems cells and vessels of different kinds occur. In Dicotyledons the ascending system is connected with the medullary sheath, and passes into the buds and leaves, while the descending system is the woody tissue sent down from the leaves between the sheath and the bark. The woody fibres of the leaves, favoured by the cambium, are developed from above downwards. In the wood the ligneous tissue of the upper leaves envelopes that of the inferior ones, while in the bark the fibrous tissue is inserted in the reverse way—the internal layer, corresponding also to the superior leaves, being the newest. The extension of the cellular tissue of the stem takes place in a horizontal or transverse direction.

The Radicular or vertical theory of wood formation has been supported by reference to the arrangement of the vascular bundles in Palms (Fig. 85) and Dracaenas, and to the development of aerial roots from different parts of the stems of Screw Pines (Fig. 66), Figs, Velloarias, and Tree-ferns. Many travellers, such as Gardiner, who examined Palms in their native countries, have espoused the vertical theory of wood formation. In these plants the bundles of woody vessels can be traced from the base of the leaves, taking a peculiar curved direction downwards, and interlacing in a remarkable manner. In many Palms the fibres burst externally through the stem, and appear as roots. In the case of Screw Pines, the formation of external or adventitious roots is very remarkable; in them the thickness of the stem is diminished below the points whence the roots proceed, as if the woody matter had appeared externally in place of proceeding internally. Adventitious descending roots are also seen in many of the Fig tribe, such as the Banyan (Fig 65) and the Peepul tree. In Tree-ferns the lower part of the stem is often much enlarged by these aerial roots being applied closely to it. Brown says that in Kingia (an Australian plant) the leaves send down, between the true stem and the bases of the petioles which form the only bark of the tree, a series of adventitious roots closely covering the stem, and resisting to a great degree the action of external destructive agents, such as fire. A further development of this root structure is seen in Barba-cenia and Velloaria, where the whole outer part of the stem is made up of interlaced roots, which are traced inwards and upwards to the leaves. In Bananas and Plantains, as grown in the hothouses of Britain, we often see roots proceeding from the base of the leaves forming the herbaceous shoot. Roots are to be seen proceeding from sound portions of the wood of Willows, and running into those which are decayed, and wounds made in the stems of trees are sometimes covered by radicular fibres sent down from the upper part.

These views of Gaudichaud and others have been opposed by many able physiologists, more especially by Mirbel, Payen, Naudin, and Trecul. Mirbel has examined in a particular manner the development of the Date, and he has been led to the conclusion that the fibres increase from below upwards, and not from the leaves downwards. He says that a Monocotyledon produces at its summit a mass of cellular tissue called a phyllosphere, into which the vessels from the stem penetrate to form the vascular system; that after this the leaves are produced; that the vessels come from the internal periphery of the young part of the stem, arising at all heights, and that the roots have at first no immediate connection with the leaves. Trecul has examined the stems of Dicotyledons, and has been led to deny the downward tendency of the wood formation. He states that after the bark has been removed, a new layer of woody tissue and bark is formed at detached points, into which the medullary rays are continued directly without the slightest interruption. He thinks that the woody tissue is a lateral development from the already existing longitudinal cells; that fresh bark is formed on the woody tissue by the development of cells from the tissue, while the medullary rays penetrate directly into the new patches of wood; and that the woody fibre is equally capable of throwing off lateral cells, which, while in immediate connection with the old fibre, exhibit more or less imperfectly the character and form of the tissue from which they arise, while the free ends are mere parenchymatous cells. According to him the fibre-vascular bundles are not continued without interruption from the extremities of the leaves to the rootlets; the diameter of the stem may increase without the intervention of ligneous fibres descending from the leaves or buds; and the tissue of the wood and vessels, as well as the medullary rays and bark, are formed in situ, independently of the tissues higher up.

Amidst these opposing views, it is difficult to come to a decided conclusion. There is undoubtedly an ascending and a descending system in plants—a stem developed in an upward, and a root in a downward direction. The leaves are also of importance in the formation of wood, and the cambium cells are the active tissue of the stem. In so far all are agreed. The points of difference are the exact relation which the leaves bear to the woody fibres of the stem, and the direction in which these fibres are developed. The peculiar arrangement of fibres in the stems of Palms, and the production of aerial roots from various stems, favour in some measure the vertical theory of wood formation; while the woody excrencences occurring in the bark of some trees, and the production of particles of woody matter in the centre of decorticated portions of wood, and at the lower part of wounds, as shown by Trecul, seem to show that woody fibres are formed in some instances without any direct connection with leaves. While the weight of authority is in favour of the views recently propounded by Trecul, there are many facts brought forward by Gaudichaud which still require explanation, and which are not easily accounted for, unless we suppose an upward and downward tendency to be impressed on the tissues of the stem and of the buds, in the same way as on the embryo at its earliest growth. Physiologists in general concur in believing, that without the presence of leaves on the stem, no woody matter is formed.

IV.—PHYSIOLOGY OF THE LEAVES.

The leaves are arranged upon the axis in such a way as to be fully exposed to the influence of air and light. They are thus enabled to perform very important functions. As regards the development of leaves, Trecul states that some are developed from below upwards, as in the Lime; others from above downwards, as the pinnate leaves of Sanguisorba officinalis and Rosa arvensis, and the digitate veins of radiating leaves; a third set, as the leaves of Acer, exhibit both kinds of development, the lobes being formed from above downwards, and the secondary venation and toothing... Botany, from below upwards; and a fourth set, as those of Monocotyledons, have their veins formed in a parallel manner, the leaf lengthening by the base of the blade or petiole. Leaves having sheaths, or their lower portion protected by other organs, grow most at the base; those of which the whole petiole is very early exposed to the air, grow more towards the upper part of the petiole. The fluids which reach the cells and vessels of the leaves undergo changes by which they are elaborated and fitted for the formation of various vegetable secretions. In ordinary plants the non-development of the leaves arrests the formation of woody matter and of many important products. Leaves have the power of absorbing carbonic acid, ammonia, water, and aqueous solutions. They also exhale a certain amount of water, and they give off gaseous matters, especially oxygen. Thus leaves, in the performance of their functions, absorb and exhale watery and gaseous substances.

1. Absorption by Leaves.

When liquids are brought into contact with the leaves of plants, absorption takes place. Bonnet found that plants of Mercurellas, with the surface of their leaves in contact with water, absorbed as well, and kept for a time nearly as fresh as those of which the roots were immersed in the liquid; that the under surface of ordinary leaves took up liquids rapidly in consequence of the thinness of the cuticle, the laxity of the cellular tissue, and the presence of stomata; and that the thick and hard epidermis on the upper surface having few stomata, presented an obstacle to absorption. The hairs which occur especially on the under surface of leaves, seem to act like cellular rootlets, and to absorb moisture. Hoffmann ascertained that liquids are absorbed by the leaves in large quantity, and that in such cases they pass downwards by the tracheae and the prosenchyma immediately surrounding them, displacing for a time the air usually contained in the spiral vessels. He states that after every fall of rain or dew there is an absorption by the leaves, and that this is followed by an immediate descent of sap. The absorption takes place with greater or less rapidity according to the nature of the leaves, and the fluid passes through the intercellular spaces, as well as the cells and vessels. The greater and the more rapid the absorption, so much the more have the fluids a tendency to enter the spiral vessels. The absorbing power of the epidermis of leaves varies. When composed of delicate thin-walled cells, with numerous stomata, the imbibition of liquids is carried on rapidly; but when the epidermal cells are hardened, and have thick walls, absorption is much impeded. Some gaseous matters are taken up rapidly by leaves. Bousingsault found that air was speedily deprived of carbonic acid by coming into contact with the leaves of the Vine for a few minutes. Chevallier calculates that the trees of a forest, during the five summer months in which they bear leaves, withdraw from the column of air around them about 1-9th of its contents of carbonic acid.

Some researches have been made by Garreau in regard to the absorption of different liquids by the external surfaces of plants, and more especially by the leaves. In making his experiments, he employed endosmometers (long tubes with large open bulbs at the end) of nearly equal calibre, the diameter of the orifice of the bulb being in all of them about half an inch, and the diameter of the tube about one-twelfth of an inch. Each epidermis, or cuticular surface, was fixed to the end of the endosmometer by means of a wax thread, and covered by wax at the margin. The fluid in the bulb of the endosmometer was a solution of one part of sugar in two parts of water. He found that the young epidermis is endosmotic, or has the power of absorbing fluids, but that it loses this property as it gets old. He attributes the absence of absorption in the epidermis of old leaves to the fatty or waxy matter which covers them, and with which they are impregnated. His conclusions are:

1. The cuticle possesses a decided endosmotic property, the intensity of which is greater the younger the organ which it covers; when leaves become old they seem to lose their absorbing power. 2. The absorption of the cuticle is greater, the less there is of fatty or waxy matter in it. 3. The cuticle which covers the superior surface of the ribs, and more especially that which covers the petiole at the point where it joins the stem, is that part of the foliar surface which has the most marked power of absorption. 4. In some instances in which the cuticle or outer skin is absorbent, the epidermis or inner layer of integument presents obstacles to absorption. 5. Simple washing with distilled water, more especially washing with soap and water, augments the absorbing property of leaves. 6. When leaves have lost their power of absorbing water, they can still take up carbonic acid.

2. Exhalation by Leaves.

a. Exhalation of Watery Fluid, or Transpiration.

The leaves of plants, in the performance of their functions, give off a quantity of watery fluid. This constitutes what is commonly called Transpiration. The quantity of liquid transpired varies according to the structure of the leaves and the nature of the climate. When the texture of the leaf is hard and dry, as in Banksias, Proteas, and many other Australian plants, or the skin covering the leaf is thick and dense, as in the American Aloe and the Oleander, the amount of transpiration is comparatively small. In this way certain succulent plants, as Cactuses (Fig. 142), are enabled to withstand the effects of dry and hot climates, without being destroyed by the great loss of water by exhalation. The thick covering of hairs on some leaves, as on those of Culcitium, seems to be connected also with the amount of transpiration. Some very hairy plants, as Shepherd's Club, have been known to resist the effects of great drought. The hairs have the power of becoming more or less erect, and of absorbing the dew, while in dry weather they lie flat on the surface and hinder the passage of fluid. In leaves with a very thin epidermal covering or skin the exhalation is great.

Schacht remarks that in the epidermis of plants the external sides of the cells become thickened generally more than the internal. They offer, especially when corky, resistance to the evaporation of the liquids in the parts filled with sap. They would completely prevent transpiration, were it not for the presence of stomata, which allow gaseous and vaporized substances to be exhaled as well as absorbed. The epidermis of the stem, as soon as it dies, is replaced by cork, which, when completely formed, prevents all transpiration, although by its porosity it may condense gases at the surface of the plant. The presence of corky matter in the cell-walls, which has been noticed by Mischlerich, may thus materially modify the functions of absorption and exhalation.

In order that leaves may perform their functions properly, there must be a certain degree of exhalation. If from the leaves being covered with soot or dirt, or with the cottony productions of scale insects, the proper amount of exhalation is prevented, much injury is done to the plant. Hence, the importance of having the leaves of plants, when growing in hothouses and conservatories, well washed and cleaned, in order that they may perform their healthy functions.

The passage of vapour through the pores of the leaf is an imperceptible process, which is constantly going on, and the existence of it is ascertained by its effects. Woodward and Hales made various experiments on the amount of exhalation. The latter found that a common Sunflower, 3½ feet high, weighing 3 lbs., with a surface of leaves equal to 5616 square inches, exhaled 20 ounces of liquid in the course of a day; a Cabbage plant, with a surface of 2736 square inches, was found to exhale, on an average, 19 ounces; a Vine of 1820 square inches, from 5 to 6 ounces; and a Lemon-tree of 2557 square inches, 6 ounces per day. He remarked that Evergreens exhaled less than plants with deciduous leaves, and he associates this with their capability to endure the cold of winter. The exhalation from leaves, according to Henslow, depends chiefly upon the effect of light on the vital powers of the plant.

Garreau made a series of experiments on the exhalation of leaves, by enclosing a living leaf between two bell-jars, one applied to the upper, and the other to the under surface, and ascertaining the quantity of liquid exhaled, by means of chloride of calcium which absorbs water with great rapidity. He found that the exhalation from the lower surface of the leaf was usually double, and even triple or quadruple, that of the upper surface. The quantity of water exhaled has a relation to the number of stomata. The exhalation is greater at the line of the ribs, or at the part of the epidermis where there is least fatty or waxy matter. The secretion of this matter in abundance during the warm days of summer, may tend to prevent the plants being injured by rain and by the heat of the sun. By impeding exhalation, it tends to retain the moisture which is necessary for the functions of the leaves.

In some plants, when water is supplied abundantly, there is a sort of distillation of liquid from the leaves. Arendt noticed this in a stalk of the Nettle when immersed in water. The liquid passed upwards in the grooves on the upper surface of the petiole, followed the ribs of the leaves, and then dropped from the apex of the leaves. From the extremity of the leaves of Richardia africana (Calla ethiopica) a watery fluid has been observed to drop in considerable quantity. The amount varies at different periods of the day, being most copious after mid-day. It ceases with the development of the spathe and organs of reproduction. A similar watery secretion has been noticed in other Araceous plants, such as Arum, Colocasia, and a plant called Caladium distillatorium; the water in these instances flows from an orifice near the point of the leaf, upon the upper surface, in which terminates a canal running along the margin of the leaf, while smaller canals, running along the principal ribs, open into the marginal one. Williamson found that from each healthy leaf of the latter plant about half-a-pint of liquid dropped during the night. Water also drops from the margins of the leaves of Canna indica, angustifolia, and latiflora. In the hollow leaves of plants, such as Nepenthes, Sarracenia, Dischidia, and Cephalotus, a quantity of watery exhalation accumulates. Voelcker analyzed the liquid in the pitcher of Nepenthes, and found it to consist of water, containing in solution malic acid and a little citric acid, chloride of potassium, carbonate of soda, lime, and magnesia.

The exhalation of watery fluid from the leaves of plants influences the climate of a country. Humboldt remarks, that plants exhale water from their leaves, in the first place, for their own benefit, but that various important secondary effects follow from this process. One of these is, maintaining a suitable proportion of humidity in the air. Not only do they attract and condense the moisture suspended in the air, and borne by the wind over the earth's surface, which, falling from their leaves, keeps the ground below moist and cool; but they can, by means of their roots, pump it up from a very considerable depth, and, raising it into the atmosphere, diffuse it over the face of the country. Trees, by the transpiration from their leaves, surround themselves with an atmosphere constantly cold and moist. They also shelter the soil from the direct action of the sun, and thus prevent evaporation of the water furnished by rains. In this way they contribute to the copiousness of streams. When forests are destroyed, as they are everywhere in America by the European planters, with an imprudent precipitation, the springs are entirely dried up, or become less abundant. In those mountains of Greece which have been deprived of their forests, the streams have disappeared. The inconsiderate felling of woods, or the neglect to maintain them, has changed regions noted for fertility into scenes of sterility. The sultry atmosphere and the droughts of the Cape de Verd islands are attributed to the destruction of forests. Dr Cleghorn states, that in large districts of India, climate and irrigation have rapidly deteriorated from a similar cause, and that the government are now using means to avert and remedy the mischief. In wooded countries, where the rains are excessive, as in Rio Janeiro, the climate has been improved by the diminution of the trees. Gardner says, that since the axe has been laid on the dense forests surrounding the city of Rio Janeiro, the climate has become dry. In fact, so much has the quantity of rain diminished, that the Brazilian government was obliged to pass a law prohibiting the felling of trees in the Corcovado range. Muller states that the cultivation of grain, which has so completely transformed one part of the wilderness of Australia, has already exercised a most beneficial influence on the increase of rain.

It is necessary to keep up the correspondence between the fluid given off by the leaves and that taken up by the roots. If the former exceeds the latter, the leaves become languid and fall off. This is one cause why plants growing in the rooms of dwelling-houses succeed badly. The atmosphere is too dry, and the exhalation from the leaves is not compensated by the fluids taken up by the roots. This cannot be remedied by an extra supply of water, for the roots are not capable of taking up the additional quantity required. Hence the use of Wardian Cases in preventing the loss caused by transpiration, and thus enabling the plants to live even in a warm and dry room.

b. Exhalation of Gaseous Matter.—Vegetable Respiration.

The leaves of plants give off gases, the nature and quantity of which vary according to the circumstances in which the plants are placed, and their state of vigour or decay. Hence leaves produce important effects on the atmosphere, and we shall find that they are employed as the means of keeping up its purity. In the year 1771, Priestley observed that plants were able to grow in air vitiated by the breathing of animals, and that they soon restored such air to its original purity. Percival confirmed these observations, and showed that air containing so much carbonic acid as to prove destructive to animal life, was rendered fit for respiration after plants had grown in it.

Jenkenhouz examined the subject more fully, and made an extensive series of experiments. In air that had been so far depraved by respiration as to extinguish a lighted candle, he placed a plant of Peppermint, and then exposed the vessel for three hours to the sun, at the end of which time the air again supported flame. When a Nettle was put into a similar portion of impure air during the night, the air was not improved; but when exposed to the sun for two hours, its original purity was restored. Such was also the case with plants of Mustard. When similar portions of the same impure air were confined in vessels with similar plants, and respectively placed in sunshine and shade, the air exposed to the sun recovered its purity in a few hours, while that in the shade continued impure. Jenkenhouz also performed experiments with immersed leaves, and found that they purified the air in the course of a very few hours in sunshine. Botany.

Senebier also instituted a series of experiments which proved the production of oxygen gas by plants exposed to the direct rays of the sun. He considered the oxygen as derived from the decomposition of carbonic acid; and he thought that plants in a healthy state do not give out carbonic acid in darkness. Ellis, De Saussure, Dambeny, and others, have corroborated these statements more or less fully. Aquatic plants appear to surpass all others in their power of decomposing carbonic acid. In some lakes in volcanic countries, where carbonic acid rises in great quantity through the water, vegetation is very vigorous, and the separation of oxygen goes on rapidly. Schleiden mentions that there is a rich vegetation round the springs in the valley of Göttingen, which abound in carbonic acid.

Physiologists still differ in regard to the actual amount of change produced in the air by leaves during the performance of their functions. Some maintain that oxygen is given off by the leaves during the day, and a moderate quantity of carbonic acid is exhaled by a process of endosmosis during night; others say that carbonic acid is exhaled by plants in greater or less quantity at all times, and that during the day it is decomposed so as to give out oxygen; while a third set of authors state that no carbonic acid is evolved by leaves in a healthy state, and that their true function is one of deoxidation, or rather decarbonization, which consists in the fixation of carbon and the elimination of oxygen.

The first of these views was for a long time generally adopted, but some recent experiments have tended to throw doubts upon it, and to confirm the views of Senebier. Mohl still supports this view. He says plants have a double respiration—one consuming carbonic acid and exhaling oxygen by day in the green-coloured organs, and one connected with a consumption of oxygen and a formation of carbonic acid in the green organs by night, and in those not green, by day and night. If we wish to speak of a respiration in plants, he says, this oxygen-consuming breathing deserves the name far more than the exhalation of oxygen by the green organs connected with the nutrient processes.

The second view was propounded by Burnett, who considers the constant exhalation of carbonic acid both by day and by night as true vegetable respiration, while the decomposition of carbonic acid during light, accompanied with the evolution of oxygen, is regarded by him as a process of digestion; respiration thus going on at all times, and consisting, like that of animals, in the separation of carbon, while digestion only goes on during light. He has been supported by Carpenter, who says that the respiration of vegetables is not an occasional process, but one which is constantly going on during the whole life of the plant—by day, by night, in sunshine, and in shade—and consists in the disengagement of the superfluous carbon of the system, either by combination with the oxygen of the air, or by replacing with carbonic acid the oxygen that has been absorbed from it. If the function is checked the plant soon dies, as when placed in an atmosphere with a large amount of carbonic acid, and without the stimulus of light which enables it to decompose the acid gas. Garreau has also recently adopted these views. Henfrey says a distinction is to be drawn between the process of respiration in which the liberation of superfluous oxygen takes place, leaving the other elements combined in an assimilated or organic condition, and that process in which the assimilated matter is again chemically altered by the oxidation of a certain amount of carbon, which is liberated as free carbonic acid by plants unprovided with leaves, but under most circumstances decomposed again by green plants. He thinks that carbonic acid is given off by living plants as a vital process even during light, and he suggests that the re-absorption of the evolved acid gas during the day has disguised the fact in most previous experiments.

The third view of vegetable respiration has been brought prominently forward of late years by Mr Haseldine Pepys. From careful experiments, conducted during several years, he is satisfied that leaves which are in a state of vigorous vegetation, always operate so as to keep up the purity of the air, by absorbing carbonic acid, and disengaging oxygen; that this function is promoted and accelerated by the action of light; that it continues during night, although more slowly; and that carbonic acid is never disengaged when the leaf is healthy. He also finds that the fluid abundantly exhaled by plants during their vegetation is pure water, and contains no carbonic acid; and that the first portions of carbonic acid gas contained in an artificial atmosphere are taken up with more avidity by the plant than the remaining portions. The giving out of carbonic acid by leaves is attributed to disease; or to a change in the healthy state of the tissues; and in many experiments, the abnormal condition of the plant may perhaps account for the appearance of carbonic acid. In some of Mr Ellis's experiments, the decaying condition of the leaves gave rise to a fallacy in the results. Cloez and Gratiolet confirm Pepys' observations. They state that oxygen is disengaged rapidly in solar light, insensibly in diffused light, and not at all in darkness, and that in the latter case no carbonic acid whatever is given off by plants.

From all that has been stated, it would appear that an absorption of carbonic acid by the leaves of plants and an elimination of oxygen takes place during daylight, and that this process ceases in a great measure during the night. The exhalation of carbonic acid by healthy leaves is still doubtful, and the appearance of this acid gas may in many of the experiments be traced to an abnormal condition of the leaves. The great function of the leaves thus seems to be deoxidation, by means of which they are instrumental in keeping up the purity of the atmosphere. This function of plants is antagonistic in its results to animal respiration; for while the latter takes oxygen from the atmosphere, and replaces it by carbonic acid, the former removes carbonic acid, fixes carbon, and gives out oxygen. The processes of respiration and combustion are pouring into the atmosphere a large quantity of carbonic acid gas, while the active leaves of plants are constantly removing it, and, under the action of light, substituting oxygen. While plants thus get carbonaceous food, the air is by them kept in a state fitted for animal life.

As the decomposition of carbonic acid is only carried on vigorously during the day, it follows that an accumulation of it will take place in the atmosphere during darkness. Saussure found, from a mean of fifty-four observations made in a country district, that the proportion of carbonic acid in the atmosphere during the night was to its proportion in the day-time as 432 to 398; or in other words, the carbonic acid in the atmosphere was diminished nearly 10 per cent. during daylight. It is said also that during summer, when animal life is more active, the proportion of carbonic acid is greater than in winter, as 7:13 to 4:79 parts in 10,000. The usual quantity of carbonic acid in the atmosphere, before being drawn into the lungs, is about 1-250th; in that returned from the lungs it is about 1-25th, or it has increased 100 times in quantity. So long as plants are kept in a vigorous and healthy state, they do not give off any carbonic acid. If, however, they are kept long in the dark they begin to fade; the green colouring matter called chlorophyll is not produced as it ought to be; the plants are blanched or etiolated, and in fact get into a state of disease. In such circumstances no oxygen is given off, but, on the contrary, carbonic acid is produced.

Experiments have been made by Draper as to the particular rays of the spectrum which are concerned in the decomposition of carbonic acid by the green parts of plants. They were made with a series of tubes half an inch in diameter and six inches long, which were arranged so that the coloured spaces of the spectrum fell on them. In these tubes water impregnated with carbonic acid and a few green leaves of Poa annua were placed. In the tube that was in the red space a minute bubble of gas was sometimes formed, sometimes none at all; that in the orange contained a considerable quantity; in the yellow ray a very large amount was found, comparatively speaking; in the green a much smaller quantity; in the blue, indigo, and violet, and the extra-spectral space at that end, not a solitary bubble. Hence he drew the conclusion that the light-giving rays and those nearest the yellow have the greatest effect in the decomposition.

It has been stated that plants, when blanched, give off carbonic acid. Morot says that in partially cotyledon plants, when exposed to the direct rays of the sun, the yellow portion of the tissue gave out carbonic acid, while the green parts gave out oxygen. Plants having no green leaves exhale carbonic acid. Thus Lory found, from thirty experiments, that Orobanche in every stage of their growth, whether exposed to light or not, absorb oxygen and give out carbonic acid. Lory took two parts of the same weight, one of Orobanche Teucrii, and the other of the leafy stalk of Teucrium Chamaedrys, on which it was parasitic, and placed them in two jars of the same capacity, filled with six volumes of air to one of carbonic acid. Both were exposed to light from 9 A.M. until 3 P.M. of the succeeding day, and at the end of that time the air in which the Teucrium was placed contained no trace of carbonic acid, while that in which the parasitic Orobanche was placed yielded a large quantity of carbonic acid and a diminished amount of oxygen.

3. Influence of Leaves on Vegetable Secretions.

By means of the processes of absorption and exhalation which are carried on by leaves under the influence of air and light, the contents of the cells and vessels are elaborated and fitted for the production of various important secretions. To the action of the leaves must be traced in a great measure the elaboration of the azotized and unazotized compounds, to which allusion has already been made. When the functions of the leaves are interrupted by non-exposure to light, or by the attacks of disease, and when plants are deprived of their leaves by injuries of various kinds, their secretions are either wholly stopped, or they become altered in their nature. When leaves are blanched by being excluded from air and light, they lose their properties, their fragrant oils and resins are not developed in a proper manner, chlorophyll is not formed, nor is woody matter produced. Potatoes grown in the shade become watery, and produce little starch in their tubers.

The importance of leaves in the production of timber is universally acknowledged. If they are prevented from performing their functions properly, by being kept in darkness or in the shade, wood is imperfectly formed; and if the leaves are constantly stripped off a tree, no additions are made to its woody layers. Some troublesome weeds with underground woody stems may be entebed and ultimately extirpated by repeatedly cutting off their whole foliage. The difference of the wood in crowded and properly thinned plantations, depends in a great measure on the growth and exposure of the leaves. Wood grows more rapidly, and the zones or circles are larger, when there is free exposure. Hence the necessity of judicious planting if we wish to have good timber. When a tree forms large circles of woody matter, and thus grows rapidly, it has been found that the quality of the timber is better than when the same species forms small circles and grows slowly.

While in the cultivation of trees, shrubs, and ordinary flowering plants, the object of the gardener is to allow the leaves to perform their functions perfectly, there are certain cases in which he endeavours to interrupt these functions, and to produce an unnatural condition, by which the plants are rendered more suitable for domestic purposes. All are familiar with the fact that blanching deprives the leaves of their green colour, and prevents them from acquiring their usual qualities. This depends on the effect of darkness in arresting the formation of chlorophyll or the green colouring matter, and in hindering the production of various secretions. In the case of Asparagus and Sea-kale, gardeners succeed by artificial etiolation (blanching) in preventing the plants from producing woody tissue—cells and thin-walled vessels being alone formed, which are delicate in their texture. The tenderness and succulence of the heart of the cabbage are due to the outer leaves obstructing the access of light. In Celery the effect of blanching is to deprive the plant not only of the woody tissue, but also of certain other secretions which render it in its ordinary condition unpalatable. It is thus distinctly proved that leaves owe their green colour to the action of light, and that it is only when light and air are supplied freely, that they can form the secretions which are required for the vigorous and normal growth of the plant.

4. Effects of Various Gases upon Leaves.—Wardian Cases.

In considering further the functions of the leaves, it is of importance to notice the effects produced upon them by different gases. The atmospheric air, with its oxygen, nitrogen, carbonic acid, and ammonia, is the gaseous mixture best fitted for the growth of plants. Certain gases in their unmixed state are poisonous to plants, while others do not seem to produce any deleterious effects farther than the retardation of growth caused by the exclusion of atmospheric air. Saussure found that a plant of Lythrum Salicaria flourished for five weeks in hydrogen gas, and the Messrs Gladstone ascertained that nitrogen, oxygen, and nitrous oxide were innocuous. Plants would not of course continue to be vigorous in such atmospheres, inasmuch as they are deprived of the carbon which is necessary for them, and which can only be procured from carbonic acid.

Plants, when exposed to light, will thrive in an atmosphere containing a considerable amount of carbonic acid, but they cease to perform their functions in an atmosphere composed of carbonic acid alone. Dansebeny found that Ferns and Lycopodiums, which are the plants most nearly allied to those of the coal epoch, can at the present day exist without injury in an atmosphere containing at least 5 per cent. of carbonic acid, and he thinks that this in some degree supports Brongniart's hypothesis as to the cause of the enormous production of carbon by the plants of that epoch. While plants in bright light can live in an atmosphere containing 5 to 10 per cent. of carbonic acid, Dansebeny ascertained that the addition of a larger percentage caused injurious effects.

In the atmosphere of towns, more especially those in which chemical and other manufactories exist, there are many gaseous and other matters present which interfere in a marked degree with the growth of plants. Every cultivator knows the difficulty of growing Roses and many valuable garden flowers in such situations. Drs Turner and Christison were led to examine the influence of gases on plants, on account of having been called upon to give evidence as to the effects of a black-ash manufactory on the vegetation in its neighbourhood. They found that many gases, even in minute quantity, injured and destroyed the leaves of plants, some of the gases acting as irritant poisons, others as narcotic poisons. The former destroyed the texture of the leaves and altered their colours, while the latter killed the leaves without producing any local effects on the textures. Sulphurous acid gas, which is very com- Botany. monly met with in the atmosphere of towns was found to be exceedingly deleterious. Where four or even only two cubic inches were introduced, along with a young Mignonette plant, into the air of a glass jar, capable of containing 470 cubic inches, the leaves of the plant became greenish-gray and drooped much in less than 2½ hours; and, though then taken out and watered, it soon died altogether. In some of the experiments, the proportion of the acid gas was in a ten-thousandth only, the quantity being one-fifth of a cubic inch, and yet the destruction of the leaves was complete in 48 hours. This proportion of the gas, although destructive to plants, is hardly or not at all discoverable by the smell. The effects of other irritant gases, such as hydrochloric and nitric acid, on the leaves of plants were also well marked. The former destroyed the whole vegetation of a plant of considerable size in less than two days, even when diluted with 10,000 parts of air.

Acid gases attack first the tips of the leaves and then extend to the stalks, and it is found that when the quantity is not great the parts not attacked generally survive, if the plants are removed into the air. Narcotic gases act very differently. Thus, Drs Turner and Christian found that 4½ cubic inches of sulphuretted hydrogen in 80 volumes of air, in the course of 24 hours, caused several of the leaves of a plant to hang down perpendicularly from their stalks in a flaccid state, without injuring their colour; and though the plant was then removed into the air, the whole stem soon began to droop, and the plant died. When 6 cubic inches of the gas were mixed with 60 times their volume of air, the leaves began to be affected in 10 hours; they became quite flaccid, but did not appear changed in colour. When the leaves had once drooped the plants did not in any instance recover when removed into the air.

The effects produced by ammonia, cyanogen, carbonic oxide, and common coal gas, are in many respects similar to those now described, viz., a drooping of the leaves without alteration of colour, and the death of the plant even though removed into the air. The phenomena, when compared with what was observed in the instances of sulphurous and hydrochloric acid, would appear to establish, in relation to vegetable life, a distinction among the poisonous gases nearly equivalent to the difference existing between the effects of the irritant and narcotic poisons on animals. The gases which rank as irritants in relation to animals seem to act locally on vegetables, destroying first the parts least supplied with moisture. The narcotic gases, including under that term those which act on the nervous system of animals, destroy vegetable life by attacking it throughout the whole plant at once—the former probably only abstracting the moisture of the leaves, the latter acting by some unknown influence on their vitality.

The experiments just detailed show the importance of attending to the nature of the atmosphere in which plants grow. The blighting effects of the air of large cities are owing to the gases contained in the smoke, and unless means are taken for guarding against these, it is not to be expected that town vegetation can be luxuriant. The common gas used in houses is also prejudicial to vigorous growth, and this combined with the dry atmosphere of rooms is the cause of plants not succeeding well in private dwellings. The transpiration from the leaves in such circumstance is very great, and it is impossible to make the roots take up sufficient moisture to supply the loss. Hence the leaves fall off and the plants become sickly.

With the view of enabling plants to grow in the atmosphere of towns, notwithstanding the fuliginous matter and gases with which it is loaded, Mr N. B. Ward invented closely-glazed Cases, in which he succeeded in cultivating tender plants, even in one of the most populous and smoky localities of London. One of these Cases is represented in Figure 143. It consists of a strong box or trough, made of well-seasoned wood, containing earth. The bottom of the box is covered to a moderate depth with gravel and broken bricks, over which the soil is spread, composed of fibrous loam, sand, and peat. The nature of the soil may be varied according to circumstances, and the box may be divided into compartments containing soils of different kinds. The soil is well watered, and the superfluous water is allowed to run freely from two holes in the bottom of the box. After draining fully, the holes are tightly closed with corks, and the glazed roof or cover, b, is fitted on carefully in a groove round the upper part of the box. This glazed cover may be formed in various ways. It is frequently made of zinc, with large panes of glass, the upper one being curved.

Plants in these Cases are enabled to stand great changes of temperature without being injured, and they are protected from noxious matters in the atmosphere, besides having always sufficient moisture. Ferns and Lycopodiuns, in an especial manner, succeed in such Cases. Those ferns which require much moisture and shade, such as Trichomanes radicans, can be grown successfully. The atmosphere, however, can be varied as regards moisture and dryness, and thus can be suited to different tribes of plants. The cases are well fitted for rooms or dwelling-houses, inasmuch as they prevent the excessive exhalation which so generally injures plants grown in these circumstances. The Cases have been applied most successfully to the transport of living plants, and many valuable productions have thus been introduced into different countries.

5. Coloration of Leaves.

The green colour of leaves depends on the production of chlorophyll, which is only developed under the agency of light. The leaves in the young bud are of a pale yellowish hue, and assume their green tint in proportion as they are exposed to light. The change of colour takes place more or less rapidly, according to the intensity of the light. The leaves of French Beans, which sprung white out of the earth, were observed by Senebier to become green in one hour under exposure to very bright sunshine. Plants, when grown in darkness, have pale leaves, which become green on exposure to light. It is said that an etiolated plant, when exposed to light, becomes green at the end of twenty-four hours, even under water. Diffuse daylight, and even the light of lamps, will cause a green coloration, but the intensity of the colour is much less than in full sunshine.

Experiments have been made in regard to the effects of the different rays of the spectrum in the production of the green colour of leaves. Senebier ascribed it to the violet rays, and Ritter and Wollaston to the chemical or tithonic rays, which are next the violet. Hunt thinks that the blue rays are the most active in this respect, while Morren, Daubeny, Draper, and Gardiner, say that the yellow rays, or those having the greatest illuminating power, have the greatest effect in producing chlorophyll, as well as in deoxidation. The subject requires further elucidation.

In temperate climates the leaves during the period of their diminished activity exhibit changes of colour which give rise to the yellow, brown, and red autumnal tints. These colours seem to depend on different states of oxidation in the chlorophyll. Hunt thinks that the brown colouring of the autumnal leaves is due to the rays called by Herschel parathermic, which can scarcely be said to have a definite place amid the calorific radiations, but which are usually most strongly manifested in the red rays. A slight tint of green was found to stop these parathermic rays, and on that account glass stained green with oxide of copper has been used in glazing the Palm-House at Kew.

Variegation in leaves is produced either by an alteration in the green chromule or chlorophyll, or by the presence of air in certain foliar cells. Sometimes a single group of cells contains the yellow product of the decomposition of the chlorophyll, as in Phalaris arundinacea picta, a variety which appears in a dry soil, and disappears in a wet one; or as in variegated varieties of Holly. At other times the epidermis separates itself from the cells lying under it in particular places, and the layer of air lying between these appears like a bright silvery spot, as in Begonia argyro-stigma and Carduus Marianus. Treviranus states that in Monocotyledons the variegations form bands parallel to the veins; in Dicotyledons, such as Carduus Marianus, the white is produced in the veins, while in such as Aucuba japonica, the yellow spots are distributed without order. He states also that variegation is sometimes visible on the upper surface of the leaves, and not on the under. Variegation, according to Morren, has its seat deeper in the leaf than what is called spotting. The latter is confined to the cuticle or skin, while the former extends to the parenchyma or cellular tissue below.

6. Irritability and Contractility of Leaves.

Certain leaves display evident movements under the influence of light, heat, and a stimulus either of a mechanical or chemical nature. The effects of light and darkness are frequently very marked in causing the elevation and depression of leaf-stalks, and the expansion and folding of leaves. The changes which take place in leaves during darkness were included by Linnaeus under what he called the sleep of plants. During darkness leaves often hang down, and, in the case of compound leaves, there is also a folding of the leaflets, either in an upward direction, as in the sensitive Mimosa, or downwards, as in Tephrosia caribea.

Very obvious movements occur in the leaves of many species belonging to the natural orders Leguminose, Oxalidaceae, and Droseraceae. Among Leguminous plants may be noticed species of Mimosa, Robinia, Eschynomene, Smithia, Desmanthus, and Neptunia; in the family of Oxalidaceae, many species of Oxalis exhibit a certain degree of irritability, but it is chiefly observed in the pinnate-leaved Biophytum sensitivum; while among Droseraceae the leaves of Dionaea muscipula have a remarkable irritability, and those of the species of Drosera also exhibit traces of it. In some plants the movements are most marked in the young state. The movements exhibited by the leaves of plants may be divided into—1. Those which depend upon the periodical returns of day and night; 2. Those, which, besides being influenced by light and darkness, are also occasioned by any external or chemical agency; 3. Those independent, to a certain extent, of external influences.

In Mimosa pudica and sensitiva, which usually receive the name of Sensitive plants, the motions of the leaves are very conspicuous. They are influenced by light and darkness, and they are exhibited on the slightest touch. In these plants the leaf, as represented in Figure 144, is a compound bipinnate one, having four partial leaf-stalks proceeding from a common petiole. The small pinnales or leaflets are expanded horizontally when the plant is in the light and in its natural state, but when it is in darkness, as well as when the leaves are touched or irritated, the pinnales fold upwards, so as to bring their upper surfaces into contact, and at length the petiole is depressed, so that the entire leaf falls down. When the whole leaves are thus folded and depressed the plant appears as if it were withered and dead. When light is introduced, or when the irritation is removed, the leaflets gradually unfold, and the leaf-stalk rises. In the ordinary state of the plant these motions go on daily. If two of the leaflets at the extremity are touched, or are irritated by heat from a lens, or by electricity, without agitating other parts, they fold upwards, and a similar movement takes place in the adjoining leaflets in regular succession from the apex to the base of the petiole. The irritation is also communicated to the neighbouring partial petiole, the leaflets of which fold in a reverse order, namely, from base to apex. The movement may be propagated until the partial petioles converge and fall down; and, finally, the general leaf-stalk is depressed. If the lower leaflets are first irritated, the foldings take place from the base to the apex of the petiole; if the middle leaflets are touched then the foldings occur on each side. The stem itself seems not to be directly concerned in the motions. It may be injured in various ways without causing contractions to take place. A section may be made of it with a leaf attached, and yet the leaflets may remain expanded. Artificial light from six lamps, according to De Candolle, caused the expansion of the leaves; and Zantedeschi states that the lunar rays also affect the motions.

The action of the wind, or any general agitation, causes the simultaneous folding and depression of the leaves; but the quick repetition of an irritation exhausts the sensitiveness towards it. It appears that the plants may become accustomed to a weak stimulus. The more vigorous the plant, and the higher the temperature to which it is exposed, the more sensitive it is. The leaf of the Mimosa is sensitive of various kinds of stimuli, such as shaking, wounding, burning, contact of irritating fluids, electric and galvanic shocks. Many chemical stimuli cause the leaves to fold. Thus the vapours of prussic acid, of chloroform, and of ether, are found to produce this effect; and in such cases the irri- tability of the leaves is either destroyed, or, at all events, a considerable period elapses before it is restored.

The Yellow-water Sensitive plant (Neptunia plena), found in the East and West Indies and in South America, exhibits irritability in its petioles and leaflets. The leaves of Venus's Fly-trap (Dionaea muscipula), an American marsh plant, are provided with a jointed blade (Fig. 145), on each half of which are placed three hairs, with swellings at their base. When these hairs are touched or irritated in any way, the two halves of the leaves close. Flies and other insects are often found inclosed in the leaf, and hence the name given to the plant. It is said that the Sundews (Drosera) of our marshes also exhibit a certain degree of contractility, but this has not been distinctly proved. Their leaves (Fig. 107) are provided with viscid glandular hairs, to which insects are often found adherent, while the leaves are partially folded.

In the case of Hedyarum (Desmodium) gyrans, a native of the East Indies, the phenomena of leaf-motions are very remarkable. The leaf, as represented in Figure 146, is unequally pinnate, having a large leaflet or pinna \(a\), at the extremity of the stalk, and two pairs of small pinnae \(b\), placed laterally. The large leaflet exhibits oscillatory lateral movements, as well as the ordinary sleep movements, in an upward and downward direction. During the day it rises and appears to have slow motion from one side to the other, so that it often is seen in an oblique position as regards the stalk; during the night it is depressed and motionless. The little pinnae, on the other hand, constantly exhibit a jerking motion, by which they first approach to each other, and then retire, the length of time required to complete their movements being about three minutes when the plant is vigorous and exposed to bright light. The leaflets exhibit motions even in darkness, although to a less extent. Other species of Hedyarum exhibit similar movements.

The cause of these phenomena is obscure. Some have supposed that they are to be ascribed to the presence of a peculiar nervous system in plants. But there is no evidence of the existence of such a system, and the motions do not require that we should have recourse to such a theoretical explanation. All may be accounted for by changes in the contents of the cells. In the case of the sensitive Mimosa, there are evident cellular swellings at the base of the small leaflets, as well as the base of the petioles. These swellings, when touched directly, communicate motion to the leaves. They consist apparently of two kinds of cells, some of which display contractility, and others distensibility. When in their ordinary state these functions are balanced; but when mechanical or chemical stimuli are applied, a change in the cell-contents takes place, accompanied with a derangement of equilibrium. When the swellings at the base of the leaflets are touched gently on the superior surface, then the liquid contents of the upper contractile cells are sent into the distensible inferior ones, and the leaflets fold upwards. This change, however, is not effected by touching cautiously the lower surface of the swellings. Again, in the swelling at the base of the petiole, the reverse is the case, for there the lower cells are contractile, and the upper distensible, and the movement caused is in a downward direction. Touching the upper side of the intumescence at the base of the petioles does not give rise to the movement. If a portion of the lower side of the swelling is removed, then the balance between its resistance and the expansive tendency of the cells on the upper side is destroyed, and the petioles remain depressed. Any irritation applied to one part of the leaf is propagated by means of the vascular system to another part, and more especially it is communicated to the distensible portion of the cellular swellings just mentioned.

In the daytime, and under the influence of light, according to Fée, the fluids drawn to the surface of the plant are kept in equilibrium by rhythmical evaporation. There is a constant renewal of fluids to supply those which have been transpired. A blow or wound, or the application of cold, interrupts the equilibrium, the circulation is deranged, and liquids pass quickly from the cells into the vessels, and thus cause distension. During the night the sap is feebly drawn to the surface, and thus a change takes place in the relative contents of the different cells and vessels. The phenomena are thus referred to changes in the fluid contents of the cells and vessels caused by certain vital actions. Mohl refers the movements partly to the distension of the cells, and partly to different states of tension in the tissues, and he considers the movement of irritability as not identical with the sleep movement. He says that the articulations are composed of numerous parenchymatous cells containing chlorophyll, each also exhibiting in its interior a larger or smaller globular mass of a substance strongly refracting light. The parenchymatous tissue, he says, exhibits a considerable distension. If a flat portion is cut longitudinally out of the middle of the joint, and afterwards this portion is cut lengthways into thin strips, the cellular tissue forming the sides of the strips immediately expands about one-fifth longitudinally, while the vascular bundle in the middle continues as before. Hence, he says, the vascular bundle appears to be too short in proportion to the turgid mass of cellular tissue of the articulation, while the latter is compressed in the direction of the longitudinal axis in the uninjured part. In the ordinary state of the plant, the expansion of the cellular tissue of the upper side of the articulation maintains the equilibrium with the cellular tissue forming the under side, and thus curvature is prevented. But if the cellular tissue is cut away down to the central vascular bundle on the upper side of the articulation of a leaf still attached to the plant, the cellular tissue of the lower side having now lost its antagonist can pursue its expansion, and the leaf becomes at once pressed upwards at a sharp angle—the reverse occurring when the cellular tissue of the under side is removed.

In the case of Hedyarum gyrans and other species, the movements are probably referable to changes in the contents of the cells and vessels, not directly induced by mechanical irritation, and only partially influenced by the stimulus of light and heat. In Venus's Fly-trap (Dionaea muscipula) the irritation of the hairs is apparently communicated by means of vessels to the cells between the two halves of the leaf-blades, in such a way that distension takes place in the lower cells, and thus the leaves close. The object of these various movements is not known.

7. Defoliation, or the Fall of the Leaf.

Leaves continue to perform their active functions for a certain length of time, and are then replaced by others. In temperate climates these functions go on vigorously during spring and summer, but towards the end of autumn they become languid. In the ordinary trees of this country the leaves fall off during winter, a latent bud having originated in their axil whence new leaves arise in spring. In warm climates the dry season often causes a similar exuviation of the leaves. This is observed in the Brazilian forests called Cattingas. The times of the appearance and of the fall of the leaves vary in different countries, and from them may be deduced conclusions as to the nature of the seasons.

The fall of the leaf has not received the attention it deserves from physiologists. The reason frequently given for this phenomenon is the choking up of the cells and vessels of the leaf by deposit of earthy and saline matters, in consequence of the process of absorption in autumn not keeping pace with the exhalation of watery fluid. There is no doubt that mineral substances do accumulate in the leaves in autumn, but there seems to be no proof that this is the sole cause of their fall. When autumn approaches, it is found that a gradual separation takes place between the leaf-stalk and the stem or the axis to which it is attached. This is not a mere accidental occurrence, but is a process for which regular provision is made. According to Inman a process of disjunction goes on from the time the leaf-stalk is fully formed until the leaf has ceased to perform its functions.

In cold climates various causes operate in causing defoliation. As the light and heat diminish there is a cessation of the functions of cells and vessels, evaporation takes place from the surface; inorganic matters accumulate in the tissues, the leaf becomes dry, its attachment to the stem is loosened, and then it either falls by its own weight, or is detached by external agencies of different kinds. Dr Fleming states, that winter is not the immediate cause of defoliation. Many leaves fall before the approach of winter, others perish in spring. He divides trees in reference to the duration of their leaves into three classes—1. Those in which the leaves cease to perform their functions when the bud is complete. 2. Those in which the leaves continue to perform their functions until new ones appear the following season. 3. Those in which the leaves continue to perform their functions for several years.

The leaves of the first class are Deciduous, and they seem to be connected with the ripening of the bud. When this takes place, these leaves change their colour and perish. In Willows, even in midsummer, many of the branches become naked from the fall of such leaves. In trees having two evolutions of buds in the season, as the Beech, the leaves produced in spring fall sooner than those which are developed on the summer shoots. Leaves of the second class Dr Fleming calls Annual. These continue till new leaves are produced, and are cast off in the order of their development. In Evergreen trees and shrubs the leaves of one season continue their functions until those of the next season are produced. The leaves of the third class Dr Fleming calls Persistent. Their duration does not seem to be regulated by the perfection of the bud, nor by the development of new leaves. They continue their functions for several years. This is the case with ordinary Evergreen Firs. In these plants the leaves of various years seem to be required for the complete formation of the stem and its secretions. On the same tree, may be seen leaves two, three, or more years old.

The sap absorbed by the roots, and which contains various inorganic matters in solution, reaches the leaves, and is thus exposed to air and light. There is a large transpiration of watery fluid, and the inorganic matters not required for the organism and secretions of the plant are stored up in the leaves, forming at times incrustations on the walls of the cells. The quantity of ash left after burning leaves varies at different periods of the plant's growth. Vernal leaves contain a small amount of ash, while autumnal ones leave a large quantity when burned. The latter contain from 10 to 30 times more ashes than the wood of the same plant.

V.—GENERAL CIRCULATION OR MOVEMENT OF THE SAP.

Plants are not provided with a circulating system like that of animals, and they do not exhibit movements of fluids to and from a common centre. Liquids are diffused throughout the whole plant by the action of cells and vessels having a different chemical constitution and different functions. One cell takes the juice from another, and acts by diffusion on the others. The cells of the rootlets imbibe by endosmosis fluid matters which are carried into the stem, and the cells of the leaves, by their exhaling functions, aid in promoting a general movement of sap throughout the whole system.

It is not easy to make experiments on the motion and course of the sap, both on account of the minuteness of the vegetable tissues, and the unavoidable injury which must be inflicted on them in any attempt to observe these living actions under the microscope. We cannot, as in animals, put ligatures on vessels, nor by an injecting apparatus send coloured matters into them. Endeavours, however, have been made to trace the course of the sap by causing the roots to absorb solutions of substances which can be easily detected by chemical reagents at different parts of their progress. Thus a weak solution of acetate of lead has been employed, which can be detected by iodine, sulphuretted hydrogen, and other tests; also a solution of ferrocyanuret of potassium, which can be tested by chloride of iron, or by sulphate of the peroxide of iron. The last has been used recently by Hoffmann in his experiments, and he finds the blue colour produced by the action of salts of iron on the ferrocyanuret a good means of tracing the course of the sap. As the Prussian blue thus formed is insoluble in water, a little care in dissecting enables us to avoid the spreading of the colour to unaffected parts.

It may be remarked in general, in regard to these experiments, that very different results followed, according as the absorption took place by the uninjured roots, or by the cut surfaces of plants. In the latter instance, the fluids were found in vessels which they did not enter in the former case. In cellular plants the sap seems to move through all parts, and is not confined to any definite set of cells. In vascular plants it appears in general that the sap enters the cells and woody vessels (and perhaps the intercellular spaces); and that the spiral vessels and those allied to them, such as annular and scalariform vessels, very generally contain air when the sap enters slowly. But when there is a rapid movement of sap either from the root upwards or from the leaves downwards, especially in Dicotyledons, then the spiral vessels take up fluids as well as air. It seems probable that the spiral vessels and their allies are receptacles for gaseous matter formed in the course of the movement of the sap.

In truly cellular plants, as Fungi, the course of the circulation has no accurately fixed boundaries, and presents no anatomical peculiarities. The fluid is found to proceed both forwards and laterally in the cells and intercellular spaces, proceeding most rapidly in those parts where the tissue is most lax. In plants such as Lichens, where the tissue is dense, and in which there is not much fluid, the sap passes with great slowness between and through the cells. In the case of mosses possessing leaves, the fluid was found to pass through the stem and fruit-stalk, and in the leaves it moved most rapidly in a peculiar layer of cells along their margin and not in the midrib. Probably the condensed cells and vessels of the midrib are concerned in the conduction of fluids from the leaves in a downward direction.

In Ferns it was observed that the scalariform vessels and closed spirals contained air, and that they did not take up any of the solution of the ferrocyanide. If the petiole of the frond is cut across and inserted in the solution, then the latter passes into the scalariform vessels, driving out the air. The leaf of the Fern, when dipped in the liquid, absorbs it, but it does not pass into the scalariform vessels. In Ferns there did not appear to Hoffmann to be any path for descending juices, and this is probably connected with their mode of growth, which is by additions to their summit (acrogens). The streaked vessels in Ferns seem to be destined exclusively for gaseous matters, while the fluids absorbed from the earth first ascend within the loose cellular tissue in the vicinity of those vessels, and are from them diffused throughout the remainder of the tissues after suitable elaboration. In Monocotyledons the solution of the ferrocyanide ascended chiefly through the elongated cells surrounding the spiral vessels, and the latter contained, in ordinary circumstances, air in their interior. In regard to the course of the sap in Dicotyledons, numerous experiments have been made. Walker, Burnett, and others made incisions into the bark and wood of trees in spring and summer, and marked the points where the sap made its appearance. In this way they endeavoured to trace the course of the fluids in the stem. Walker concludes, from his experiments, that the spring sap begins to flow at the root, that it ascends slowly upwards, and bleeds successively as it ascends to the very extremity of the tree; that there is no descent of sap until after the development of the leaves. Burnett cut notches in the trunks of various trees in spring, at different heights in each tree, from one to six feet from the ground; and in every instance the sap was seen distinctly exuding from the lowest side of the lowest section first, and progressively rising to the others day by day. The chief current was axial in the first instance, and afterwards the sap entered the branches. To the progress of the sap in the direction of the axis he attributes the early development and vigour of terminal buds. Mohl states that when a ring of bark is taken off, the flow of sap to the parts above it is not interrupted; but if a portion of the wood is carefully removed without injury to the bark covering it, then the portion of the plant above the wound dries up at once.

Hoffmann bored holes in the stems of trees, such as the Sycamore, and inserted quills with the inner ends cut off obliquely, and the orifices looking upwards—the quills being cemented in their place. He made experiments with the spring sap, by inserting the roots of plants in a solution of the ferrocyanuret of potassium, and testing the fluid at different heights as it was discharged in drops from the quills. He found that the exudation of the sap in spring occurred obviously earlier in the lower than in the upper part of the stem, and that the ascent of the fluid was confined to that side of the stem which corresponded to the absorbing root.

In spring, it appears that the sap, as it increases in quantity, besides filling the cells and vessels of the wood, also enters the spiral vessels. This is the time when the plant bleeds freely on being wounded. As the leaves expand, transpiration of fluids takes place, and then the spiral vessels contain air. In some climbing plants, this state of fulness in the spirals, as well as in the wood, continues permanently. After the leaves expand, in ordinary trees the conduction of sap takes place through the newer woody vessels and cells, and not through the fibro-vascular tissue. The circulation of the sap during summer, when the leaves are most active, differs from that in spring, in the circumstance that the trees do not bleed when wounded. In summer, as in spring, there exists a rapid ascent of crude sap; but in addition to this, there is a descent of the elaborated fluids from the leaves to all parts of the plant. Hoffmann states that there is also a descent of unelaborated fluids after every shower of rain.

Some authors believe that the chief channels by which the sap ascends are the intercellular canals, which are more or less continuous from one end of the plant to the other, and that from them it passes to the other parts, each cell and vessel taking from the general circulation what is required for its growth and nutrition. In this view the cells and vessels would be regarded as secreting organs, acting in various ways on the general mass of crude sap, and separating from it by a chemico-vital action different liquid and gaseous matters. The recent experiments of Hoffmann do not support this theory of sap movement, and the general opinion of physiologists appears to be that in its upward progress the sap passes through the newer pletenchyma, as well as through the intercellular spaces, until it reaches the leaves, where it is elaborated. The different layers of wood convey sap in different quantity, the youngest being those chiefly concerned in the process. The conveyance of sap is not carried on by the old layers of wood when they become hardened by deposits. Hence trees with a large amount of hard wood, and a moderate quantity of sap wood, dry readily, while trees, like the Birch, with a large quantity of albumum, have sap movements even in the central layers of wood.

While such is the way in which the sap of Dicotyledons ascends, it is not easy to trace the mode of its after-diffusion. The usual opinion is, that after undergoing changes in the leaves and other green organs, it descends in the direction of the bark, and is thence conveyed to all the active cells and vessels of the stem. Experiments similar to those already detailed were made by Walker and Burnett as to the descent of the sap. When incisions were made in the bark, after the sap had reached the leaves, it was found that the upper portion of the cut was first moistened apparently by liquid from the upper part of the stem. If a complete ring of bark is cut off, then the growth of the portion below the wound ceases, the thickness of the stem is not increased, and, in the case of the potato, according to Mohl, no tubes are formed. At the same time the part of the stem above the wound increases much, and, in the case of trees, a thick layer of wood is formed. It would thus appear that there is a descent of elaborated sap from the leaves towards the bark, and that from this it is diffused through the rest of the tissue. Ranney thinks that the descent is through the vessels, and not the cells nor intercellular spaces; and Schultz considers the laticiferous vessels as those through which the elaborated sap descends.

Thus, as represented generally in Figure 147, the sap in a Dicotyledonous tree describes a sort of circle not in determinate vessels, but by a definite path, through different parts of the plant; passing upwards from the roots, \(a\), through the newer woody tissue, \(b\), reaching the leaves, \(c\), and after elaboration descending towards the exterior of the trunk, \(d\), whence it is diffused in various directions, both internally and externally. An absorption of water, containing various matters in solution, is constantly going on through the extremities of the rootlets. This crude sap is carried forward through the cells, vessels, and intercellular passages, by a force which acts by propulsion. The stimulus of light, acting on the cellular tissue of the leaves, or on green stems when no leaves are present, enables these parts to elaborate the organic compounds which are necessary for vegetable nutrition. The leaf-action may be reckoned one of attraction or suction. The diffusion of the elaborated matters constitutes the descent of the sap. Gaseous matters are also carried up with the sap.

Various causes conspire in originating and keeping up the movement of the sap. During winter, when vegetation is arrested, the cells of perennial plants are filled with albuminous and starchy matters. The conversion of starch into sugar in spring will at once determine an endosmotic action in the cells. The cells of the root, with their delicate walls, allow the fluids from the roots to pass readily by imbibition. A physico-chemical endosmotic action takes place, by which the fluid is propelled upwards. As the sap is constantly parting with its fluid contents, more especially when it reaches the leaves, the fluid in the upper cells is thickened, and consequently the thinner fluid below passes in by endosmosis. In addition to this, there are vital actions going on in the cells and vessels, which give rise to a constant interchange of ingredients.

Schacht says the property which certain cells have of absorbing and elaborating one substance more abundantly than another, produces an ascending and a descending current. It is possible that each cell may direct the substances it holds in solution upwards, laterally, or downwards, according to the demands of the neighbouring cells. The current of sap will consequently be directed according to the wants and the degrees of vital activity of cells having different functions. The active processes of cell-formation going on at the extremity of the stem powerfully promote the ascent of nutritive juices. As the cambium of the vascular bundles extends from the extremity of the root to the apex of the stem, there is a constant transmission of fluids from cell to cell. As new cells are constantly formed at the extremity of the stem, by means of which azotized and other matters are consumed, there is a constant demand for a supply from below. The exhalations going on in the leaves naturally give rise to a constant flow of fluids to supply the place of those which have been carried off. The capillary action of the intercellular canals may also aid in the movement, in proportion as watery fluid is removed from their extremities.

The various physical, chemical, and vital causes operating in the movement of the sap may be thus enumerated:

—Endosmotic acting as a vis a tergo or propelling power, and commencing in the cells of the root; chemico-vital actions causing changes in the contents of the cells and vessels; capillarity in the intercellular canals; and a vis a fronte or attracting power depending on the transpiration from the leaves. Heat and light materially promote the movement of the sap.

The force with which the sap ascends in the stem was measured by Hales by means of an apparatus such as is represented in Figure 148. A bent tube, \( f \) \( b \), was firmly attached to a stem, \( a \), the top of which had been cut off, and the force of the sap was estimated by the rise of the mercury previously introduced into the tube, so as to fill the curvature between \( e \) and \( f \). The force of the sap in one experiment was equal to 38 inches of mercury, which Hales states is nearly five times greater than the force of the blood in the crural artery of a horse, and seven times greater than the force of the blood in Brucke found that in a Vine, the spring sap, having a specific gravity of 1·0008, raised a column of mercury to the height of 14\(\frac{1}{2}\) inches, and therefore exerted a pressure equal to that of a column of water 195 inches high. In another experiment sap of specific gravity 1·0009 raised the mercury to the height of 17\(\frac{1}{2}\) inches.

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**CHAPTER III.**

**REPRODUCTIVE ORGANS OF PLANTS.**

I.—ANATOMY OF THE REPRODUCTIVE ORGANS.

I.—REPRODUCTIVE ORGANS OF FLOWERING PLANTS.

The flower or Floral organs concerned in the production of seed, containing the young plant, are called Organs of Reproduction. In Dicotyledons and Monocotyledons they are usually obvious, and hence these plants are called Phanerogamous or Phanerogamous (φανερός, to show, or φανέρος, conspicuous, and γάμος, marriage), while in Acotyledons they are obscure, and hence the plants are called Cryptogamous (κρυπτός, concealed, and γάμος, marriage), the former being Flowering plants, the latter Flowerless.

1. The Inflorescence.

This term designates the arrangement of the flowers on the flowering stem or branch. Flowers are produced from flower-buds, as leaves are from leaf-buds. These two kinds of buds have a resemblance to each other as regards the arrangement and the development of their parts; and it sometimes happens, from injury and other causes, that the part of the axis which, in ordinary cases, would produce a leaf-bud, gives origin to a flower-bud. It will be afterwards shown that, morphologically considered, the flower is to be looked upon as a shortened branch bearing parts analogous to leaves. The flower-bud contains either one or many flowers.

Bracts.—Like leaf-buds, the flower-buds arise either from the extremity of an axis, and are then terminal, or they are produced from the axil of leaves called Bracts. These bracts are sometimes like the ordinary leaves, as in many species of Speedwell, Periwinkle, and Pimpernel, where they bear single flowers, and in the common Bugle, Dead-nettle, and some species of Veronica, where they produce several flowers. They have the colour of leaves in such instances, and consist of cells and vessels, similarly arranged, in the form of parenchyma, ribs, and veins, with epidermis and stomata.

Bracts, however, in many plants, as regards colour, size, and form, present a different appearance from leaves. In Amherstia nobilis, and in some species of Salvia, they are large, and of a fine scarlet colour, so as to give a marked character to the flowers. In Palms, and in species of Arum, the bracts are large and sheathing, and are called Spathe; they inclose numerous flowers, supported on a common succulent stalk, called a Spadix. In some South American Palms, such spathes inclose upwards of 200,000 flowers, and they are sometimes twenty feet long. In the species of Narcissus (Fig. 149) and Snowflake, sheathing bracts are seen. In Grasses, the bracts constituting the outer covering of the spikelets of flowers are called Glumes (Fig. 150, gl).

In the case of numerous flowers on a common stalk, the bracts are often numerous also, and are arranged in a whorl or Involute, as it is called. An assemblage of involucral bracts, called phyllaries, is seen in composite flowers, such as the Daisy, Dandelion, and Marigold (Fig. 151), and in Umbelliferous plants, such as Hemlock. In some Umbelli-PL CXX. Botany.

There are two rows of bracts in each head of flowers—one, denominated the general involucre, at the base of the large umbel; the other the partial involucre, or involucel, at the base of the smaller umbels, or umbellules.

In Fool's Parsley (Aethusa Cynapium), the involucre consists of three deflexed leaflets. The bracts connected with the flowers, in the catkins of the Poplar, of the Willow, the Walnut, and other amentiferous (catkin-bearing) plants, are called Scales.

Bracts sometimes fall off when the flowers expand; at other times they continue during flowering, and, in certain instances, they form part of the fruit. The cup (cupula) of the Acorn (Fig. 132, a), and the husk of the Hazel-nut, are formed by bracts; so also are the scales of the Hop-fruit, of the Fir-cone, and of the Pineapple.

Bracts are said to be empty when they do not give origin to flowers. Thus, in Salvia Horminum, the top of the flowering axis ends in a series of coloured empty bracts, and in the Pine-apple plant the fruit is terminated by a crown of leaves, which are to be considered as empty bracts, terminating the axis. The outer row of scales in the involucre of some compound flowers consists of empty bracts, which occasionally produce buds, as in the case of the Hen-and-chickens daisy. In Cruciferous plants, such as Wallflower, and in the Borage tribe, such as Forget-me-not, bracts are very rarely developed, and hence they are called elonctated.

When an axis bearing numerous stalked flowers arises from a bract, there are sometimes smaller leaves, called Bractelets or Bracteoles, at the base of the small flower-stalks. When bracts or bractelets are placed, so as to be close to the outer envelope (calyx) of the flower, there is occasionally some difficulty in determining what parts are to be referred to each of these organs. In the Mallow tribe the outer calyx (epicalyx) seems to be of this nature. When bracts adhere to the flower-stalk and become decurrent, as in the Lime-tree (Fig. 153), they appear like winged branches, giving origin to the inflorescence.

Flower-stalk.—The axis bearing the flower or flowers is called the floral axis. It is a branch coming from a flower-bud. The term Peduncle is that usually given to a stalk supporting a single flower, or numerous flowers, which are either sessile (applied closely to the peduncle) as in the catkin, or are placed on stalks called Pedicels. When the peduncle proceeds in a straight line from the base to the apex of the whole inflorescence, it is often called the Rachis, or axis of inflorescence. A peduncle arising from a stem, either subterranean or close to the ground, and bearing a solitary flower, as in the Primrose, or bearing numerous stalked (pedicellate) flowers, as in the Cowslip, Narcissus (Fig. 149), or numerous sessile flowers, as in the Daisy and Dandelion, is called a Scape or Radical peduncle. In the female flower of Vallisneria (Fig. 22, b), the scape is spiral, and uncoils, so as to allow the flowers to appear above the surface of the water in which the plant grows.

The peduncle is usually rounded like a branch, but this is by no means its invariable form. Thus, in various species of Butcher's-broom (Fig. 154), and Epiphyllum, it is a broad leaf-like (phyllod) expansion. In the Cashew-nut* the pedicels supporting single flowers become succulent, and are used as food. When the peduncle bears numerous flowers, in place of being elongated, it sometimes is shortened and thickened, especially at its apex, so as to form a broad flattened disk, as in the Thistle and Dandelion (Fig. 155), a conical projection, as in the Daisy, a concave surface, as in Dorstenia (Fig. 156), or a hollow fleshy pear-like body, as in the Fig (Fig. 157). The peduncle is transformed, in some instances, into tendrils or spines, at other times its apex is hollowed out, so as to form part of the calyx, as in Eschscholtzia,* or of the fruit, as in Hovenia. Flower-stalks, bearing hairs in place of flowers, occur in the Wig-tree (Fig. 158).

The arrangement of the flowers on the peduncle or floral axis exhibits considerable variety. The simplest kind of inflorescence (floral arrangement) is that in which single flowers are supported on flower-stalks, as is seen in the Gentianella, and in the common Periwinkle, the Pimpernel, and Fumitory. In these instances there is a difference in the mode of floral development. In the Gentianella (Fig. 159) when the floral axis elongates, they form a raceme. If the

flower, b, with two leaves at its base, terminates the general or primary flowering axis, a; in the Fumitory (Fig. 160) the floral axis elongates, producing leaves, while the flowers are borne on secondary axes or stalks, which are axillary and lateral. In the former case the axis is arrested in its growth, and the inflorescence is Definite or Determinate; in the latter the axis is progressive, and the inflorescence is Indefinite or Indeterminate. These plants illustrate, in their simplest forms, two marked forms of Inflorescence, which it is necessary to bring more fully under notice.

Indeterminate or Indefinite Inflorescence.—The simplest form of this inflorescence is that in which the flowers arise singly from the axil of ordinary leaves, which, in this instance, serve the purpose of bracts, while the axis goes on elongating and bearing leaves at its apex. In place of a single flower, however, there are frequently several flowers produced on a floral axis in this kind of inflorescence; as is seen in some species of Speedwell, in which there arises from the axil of a bract a cluster of flowers expanding in an ascending series from below upwards. As the flowers in the indefinite inflorescence are produced like buds in the axils of leaves, they are denominated Axillary; and, when numerous, they follow the ordinary law of leaf development—the lowest (i.e., those next the primary axis), expanding first when the floral axis is elongated (Fig. 160); or the outermost when the axis is depressed or abbreviated (Fig. 151). The expansion of the flowers, in such cases, is denominated Centripetal, in consequence of proceeding in a progressive manner towards the centre or apex.

Axillary flowers, on elongated and shortened axes, present different forms of inflorescence, according as the flowers are stalked or sessile, the stalks simple or branched, and equal or unequal in length. When the primary floral axis (peduncle or rachis) lengthens and bears equally stalked (pedicellate) flowers, each originating from a bractlet, a Raceme is produced, as in the Hyacinth, Currant, and Fumitory (Fig. 160). In this instance, the lowest flowers, i.e., those next the primary axis, are first expanded, and the others follow in succession from base to apex. When the raceme has the lower flowers supported on longer stalks than the upper, in such a way that all form nearly a level top, as in the Hawthorn, and some species of Cerasus (Fig. 161), a Corymb is formed. In Cruciferous plants the flowers, when first produced, frequently appear as a corymb, and the primary axis of a raceme is shortened, so that the floral stalks all proceed from apparently the same point, forming nearly equal radii, as in the Cowslip, an Umbel is produced. In the indefinite umbel, the outermost flowers, i.e., those of the circumference, expand first. The simple Raceme, Corymb, and Umbel, may become compound by the stalks of the flowers branching. In the case of the umbel, the branching takes place by the secondary stalks coming off from a point like radii of a circle, in the same way as the primary ones did (Fig. 162). When bractlets occur at the base of the primary stalks, or, in other words, at the base of the primary umbel, they are arranged in a whorled manner, and form an Involute, and such is also the case with the bractlets at the base of the secondary flower-stalk or secondary umbel. The secondary, or partial umbels, are called Umbellules, and the verticillate bractlets receive the name of Involute. In some instances, as in Fool's Parsley, there is no general involucre, but simply an involucel (Fig. 163, b); while, in other cases, as in Fennel, neither involucre nor involucel are developed. Compound umbels are frequent in... In compound inflorescences there occurs a combination of these forms. Thus, the primary divisions may be racemose, or corymbose, or umbellate, while the secondary are of a different nature. A raceme in which the secondary branches assume the form of a corymb, or a corymb in which the secondary branches are racemose, is called a *Panicle*, a form of inflorescence met with in many grasses, and in some rushes.

This term, however, is rather vaguely applied, and includes often definite, as well as indefinite, forms of inflorescence. It is usually applied to any loose racemose inflorescence in which the stalks are irregularly elongated and branched. When the panicle is shortened, as regards its secondary branches, and forms a compact cluster resembling a bunch of grapes, as in Lilac and Horse-chestnut, it is called a *Thyrus*.

In the instances of inflorescence which we have noticed, the flowers are all supported on stalks either of the same or different lengths. When the flowers are sessile, i.e., without stalks, different forms of the indefinite inflorescence arise. A raceme, with sessile flowers, becomes a *Spike*, as in Plantago (Fig. 164). In grasses the flowers are arranged in small spikes called Spikelets (*Locustae*), as seen in Figure 165, and these spikelets are themselves arranged either in a panicked form, as in Oats, or in a spiked form as in Wheat. The latter may be called a compound spike, consisting of a series of small spikes sessile on a common rachis. Occasionally, as in Egyptian wheat, several compound spikes proceed from the top of the stalk or culm. A *Spadix* is a succulent spike, inclosed in a sheathing bract called a Spatha, as in the Cuckow-pint* (Fig. 166), and *Ethiopian Calla*, where it is simple, and in Palms, where it is branching and compound. A *Catkin*, or *Ament*, is a spike having scaly bracts. It occurs in the Willow (Fig. 167), the Walnut, the Hazel, the Birch, the Poplar, and in many other trees which are hence called *Amentiferous*.

Catkins bearing sterile flowers only, generally fall off early, and in one piece. Some restrict the term catkin to such deciduous forms of inflorescence; while others include also the fertile scaly spikes of Hazel, of Birch, and of Willow. The catkin is sometimes branching, i.e., produces numerous separate catkins on a common axis, as in the male flowers of the Fir. The *Cone* of the Pine, Spruce, Fir, and other cone-bearing plants, is a female spike of flowers with hard scales covering naked seeds, while the *Strobilus* of the Hop is a similar kind of spike with membranous scales covering seed-vessels. Some of these modes of inflorescence determine the nature of the fruit.

In the Spike, the Spadix, and the Catkin, the floral axis is elongated. Other cases occur in which sessile flowers are produced on a shortened axis. The *Head* (*Capitulum*) is a congeries of sessile flowers, supported on a more or less flattened axis (receptacle), and expanding centrifugally. In the American Button-bush the heads are globular, in some species of Teazel elliptical, while in Scabious, and in Composite plants, as Sunflower, Dandelion, Thistle, Burdock, and Marguerite (Fig. 151), they are somewhat hemispherical, with a flattened, slightly hollowed, or convex disk. In the latter class of plants, besides the general bracteal envelope, called the involucre, there are frequently *chaffy* and *setose* bracts at the base of each flower. In Dorstenia (Fig. 156) the receptacle of the flowers varies from a flattened disk to one in which the edges are incurved and turned upwards. When this incurvation of the receptacle is complete, so as to form a hollow cavity bearing the flowers inside, the inflorescence is like that of the Fig (Fig. 157). By this mode of formation the flowers at the circumference are turned towards the apex, while the real centre remains next to the stem of the plant.

**Determinate or Definite Inflorescence.**—In this inflorescence, the flowers, in place of arising from axillary buds, are considered as represented by terminal buds, beyond which the axis does not extend. The simplest form is that in which a single floral axis is produced, terminated by a solitary flower, as in Gentianella (Fig. 159), with two opposite leaves, e, at the base of the inflorescence. When such an inflorescence branches, it is by the production of axillary buds, whence arise floral axes, terminated, as the first axis, by solitary flowers. The axes are thus arrested in their development, and do not grow in an indeterminate manner. This kind of inflorescence is very commonly associated with opposite leaves, but it occurs also in plants with alternate leaves, as Lint.*

If such a plant as Gentianella, with opposite leaves, produces additional flowers, it does so in a descending series, that is to say, the buds produced by each of the opposite leaves on the stem (Fig. 159, c), and bearing solitary flowers, expand after the flower terminating the primary axis, and successively later as we proceed downwards. Thus, the expansion of the flowers is *centrifugal*, i.e., farther and farther from the central terminal bud of the primary axis, and later as regards time. A racemose or spiked inflorescence of this kind would be at once distinguished by the upper flowers being first expanded, and not the lower, as in the indefinite... Botany.

raceme and spike. The order in which the flowers expand determines the nature of the inflorescence. Attention must be paid to the axis terminating in a single flower, to the bract which it gives off laterally, and to the flower-bud produced between the bract and the axis.

When the different floral axes in the definite inflorescence come off close to each other, and are much shortened, there is often apparent confusion in the arrangement, and it is only by noticing the development of the flowers in the different clusters that we can pronounce on the nature of the inflorescence. The branched kind of definite inflorescence is seen in the Cyme. This is a corymbose inflorescence, more or less branched, forming a cluster of flowers, which is either flattened at the top, or has a rounded contour. It is illustrated in the Elder, the Hydrangeas, and the Laurustinus. It appears like a combination of the umbel and corymb, but is known by its centrifugal floral expansion.

The mode in which the cyme is formed may be studied in the common Spearwort, and other species of Chickweed. In them, as shown in Figure 168, there is a solitary flower, \(a\), which terminates the primary axis, and has two opposite leaves, \(b\), at its base. Each of these leaves (bracts) gives origin to flower-buds, which form axes, \(c\), ending in solitary flowers. Each of these secondary axes in their turn bear opposite bracts, or leaflets capable in the same way of forming tertiary axes, with solitary flowers, and so on until the plant is exhausted, or the axes produced have no leaf-nodes. This division, by pairs of axes, forms a spreading, loose, dichotomous (dividing by pairs, \(b\), \(a\), in two ways, and \(r\), \(o\), a section) cyme. If three whorled leaves develop axes, the cyme becomes trichotomous (dividing by threes). Sometimes the two bracts on the axis do not produce flower-buds, and then the primary axis, with its single flower, is alone present, with two empty bracts on the stalk, as seen in the Heart's-ease (Fig. 169, \(b\)) which produces a unifloral cyme.

At other times the primary axis produces a solitary flower, and only one of the bracts develops a flower-bud, as in the common Bind-weed, in which we meet with bifloral cymes, and also unifloral cymes.

If the flower-buds on one side of a dichotomous cyme are the only ones developed, it becomes unilateral, and often turns round in a peculiar way, so as to resemble a snail, or the tail of a scorpion, and hence it is denominated helicoid or scorpionoid. The terms gyrate and circinate are also sometimes applied. The same thing occurs also in alternate-leaved plants, where each leaf or bract produces one flower, and a flower-bud which elongates into an axis between the first flower and the bract. In such cases the flowers seem to be placed opposite the leaves, and when the leaves disappear, or are abortive, as in many of the Borage tribe, it is difficult to determine whether the inflorescence is a one-sided (unilateral) raceme, or a series of single-flowered axes, produced in a racemose manner. The appearance of the helicoid cyme is represented in Figure 170, in the case of the Forget-me-not; on the axis a leaf, \(c\), gives origin to a flower-stalk, ending in a solitary flower, \(a\); there are no bracts developed on this primary floral axis, but two racemose cymes, \(b\), are given off, each of which curls up in a circinate manner. These cymes are formed by a series of single-flowered axes, which are produced in a secund manner, i.e., only on one side. The theoretical formation of this inflorescence is given in Figure 171, where the primary floral axis, \(I\), ends in a solitary flower, and so do the other axes from 2 to 10. The small dotted lines indicate the points where floral leaves (bracts) occur. The expansion of the flowers is centrifugal. The flower of axis 1 expands first; this axis gives origin to a flower-bud forming axis 2; in its turn axis 2 expands its solitary flower, and gives rise to axis 3, and so on. Thus, the inflorescence is composed of a series of unifloral axes produced from each other, and not alternating to right and left, but always developed on one side, forming a broken line, which has a tendency to return upon itself. In the diagram ten unifloral axes are shown, each bearing a solitary flower. When the bracts are abortive, as in the Borage tribe, the nature of the inflorescence is not detected at first sight. The formation of the different axes between the previously expanded flower and the bract, indicates the nature of the inflorescence. When the internodes of such a floral axis are shortened, and the bracts disappear, some anomalous inflorescences are produced, as in Solanaceae. The appearance of a peduncle opposite a leaf leads often to a correct conclusion in regard to the morphology of the inflorescence; in the same way as has been already noticed in the case of the tendrils of the Vine, which are leaf-buds producing separate axes, in a centrifugal manner. In some kinds of cymose inflorescence the flowers are sessile on an elongated axis, forming a cymose spike; in other instances they are nearly sessile, and form a rounded head or short spike, called a Glomerulus, as seen in species of nettle, and in the Box.

Sometimes stalked flowers arise from the same part of the axis, in the form of a cluster, called a Fascicle, as in the Mallow (Fig. 172), and in species of Pink. In the case of Labiate plants, as Mint, and Dead-nettle (Fig. 173), the flowers appear to be in whorls, but in reality they arise in two clusters or fascicles, called Verticillasters, which are cymes bearing a few nearly sessile flowers, expanding centrifugally. Each cluster is produced from one of the opposite leaves. What are properly called whorled flowers are seen in the Common Marigold (Hippuris vulgaris), in which each leaf of the whorl produces a single flower.

Mixed Inflorescence.—There are certain kinds of inflorescence in which there is a combination of the definite and indefinite forms. These have been called Mixed. They are by no means uncommon in the Vegetable Kingdom, and they require to be studied carefully. In Composite plants, the branches bearing the heads of flowers (capitula) are often developed centrifugally, while in the individual heads the expansion is centripetal. The general inflorescence, in such a case, may be said to be definite, while the partial inflorescence is indefinite. Thus, in Figure 174, the central head \(a\) of flowers is expanded, while the others are only partially so; the inflorescence is mixed, and the whole puts on the aspect of a corymbose cyme, with the flowers in each head centripetal.

In Labiate plants (Fig. 173) the general inflorescence is centripetal, while the verticillasters are centrifugal.

2. The Flower and its Different Parts.

a. Symmetry and Morphology of the Flower.

The term Flower, in botanical language, is not confined to the mere showy parts in which the gay and brilliant hues reside, but embraces all the organs, however inconspicuous, which are concerned in the production of seed. These organs, or parts of the flower, must all be considered as modifications, or, as it may be more properly expressed, analogues of leaves. In their structure and arrangement they are similar to the foliar organs, and they follow the same laws of development. When a student, therefore, has acquired a knowledge of the anatomy and arrangement of leaves, he is prepared to enter upon the consideration of the floral organs.

When the flower is complete it consists of four whorls (verticils), placed alternately within each other. The two internal are the Stamens and Pistils, which are the essential organs of reproduction, and the two external are the Calyx and Corolla, constituting the floral envelopes, or protective coverings.

In Figure 175, an ideal section of a complete flower is given, each whorl consisting of five parts, which are arranged alternately. In Figures 176 and 177 the parts of the flower are represented: the calycine whorl (calyx), \(c\), the corolline whorl (corolla), \(p\), the staminal whorl (stamens), \(e\), and the pistilline whorl (pistil), \(s\), being all inserted into a common receptacle, \(r\), which may be considered as the termination of the peduncle, ped, or flower-stalk.

The Calyx is the outer covering (Fig. 176, \(s\)), formed of whorled leaves, called Sepals, which are generally of a greenish colour. The Corolla is the next covering, composed of whorled leaves, called Petals (Fig. 176, \(p\)), often showy, arranged alternately with the sepals. The calyx and the corolla are sometimes included under the common name of Perianth or Perigone (\(\tau\pi\eta\alpha\), around, \(\alpha\tau\delta\omega\sigma\), flower, and \(\gamma\alpha\pi\eta\), offspring), especially in cases where both are similar in appearance, as in the Tulip. A flower with a single perianth (Fig. 178) has a calyx only, while one with a double perianth may be considered as having both calyx and corolla. Some restrict the term perianth to cases where the envelope surrounds a staminiferous flower, while perigone is applied to the envelope of a flower having both stamens and pistil, or a pistil only.

The Stamens (Fig. 177, e) are placed within the petals, with which they alternate. Each stamen consists of a peculiar folded leaf, called the Anther (Fig. 179, a), either sessile (unstalked), or supported on a stalk, denominated a Filament (Fig. 179, f), and containing powdery matter called Pollen (Fig. 179, p), which is discharged through slits or holes. The whole staminal whorl, taken collectively, is styled the Androecium (ἀνδρος, male, and ἐκτίσις, habitation).

The Pistil is the central organ (Fig. 180), below and around which the other floral whorls are arranged. It consists of one or more folded leaves, called Carpels (καρπός, fruit), either separate (Fig. 181), or combined (Fig. 180), and collectively forming the pistilline whorl, which is denominated the Gynoecium (γυνή, female, and ἐκτίσις, habitation). The parts distinguished in the pistil are the Ovary (Fig. 180, o), which is the lower portion inclosing the Ovules destined to become seeds, the Stigma (Fig. 180, g), a portion of the loose cellular tissue, uncovered by epidermis, which is either sessile on the apex of the ovary, as in the Poppy, or is separated from it by a prolonged portion called the Style (Fig. 180, s). The essential organs must be present, in order that seed may be produced, but the floral envelopes may be wanting, and still the reproductive functions may be performed. When both calyx and corolla are present, the flower is Dichlamydeous (διά, twice, κλαμύς, a covering), when the corolla is wanting, the flower is Monochlamydeous (μόνος, one), and when both are wanting, it is Achlamydeous (α, privative).

All the organs of the flower are attached to the extremity of the flower-stalk, and the part on which they are situated has received the names of Thalamus, Tonus, and Receptacle (Figs. 177, 180 r). The different organs are verticillate leaves, produced at nodes which are placed close to each other, without the intervention of marked internodes. Each organ forms one or more whorls, and the parts of each whorl are

In certain instances the internodes are lengthened, and thus the different whorls are separated from each other, just as in verticillate leaves. Thus, in some plants of the Caper tribe, there is an enlarged, rounded, disk-like receptacle (anthophore, ἀνθός, flower, and ἐκτίσις, to bear), bearing the petals, from the centre of which arises a stalk or internode (androphore, ἀνδρός, stamen), bearing the stamens, and finally, another lengthened internode (gynophore, γυνή, pistil) bearing the pistil. In some cases the pistil is stipitate, or supported on a stalk which proceeds from the centre of the receptacle. This is seen in the Caper-plant, in the Passion-flower, in some of the Chickweed order, and in Fraxinella (Fig. 182).

In the Geranium, the part of the receptacle bearing the pistil is prolonged in the form of a long beak-like (rostrate) process, to which the styles are attached (Fig. 183, a). In the Strawberry (Fig. 184) the receptacle, after giving origin to the calyx, corolla, and stamens, becomes enlarged and succulent, bearing the parts of the pistil on its surface, and constituting what is commonly called the fruit. The Sacred Bean of India and of the Nile (Nelumbo), has a large top-shaped (turbinate) receptacle inclosing the pistils. In the fruit of the Rose the portion of the receptacle (Fig. 185, re), bearing the parts of the pistilline whorl, or, is adherent to the inner surface of the calyx, co. In some monstrous specimens of Avena and Rose there is occasionally an unusual development of the central part of the receptacle, so that the pistilline leaves become arranged alternately on an axis which ends in an abortive flower-bud.

The leaves and the different parts of the flower are considered by botanists as homologous (ὁμολογοῦν, having an agreement). In other words, they are constructed on the same plan, and the forms which they assume depend on the nature of the functions which they are required to perform. Leaves being concerned in nutrition and in the assimilation of food, assume an arrangement and colour fitted for these purposes, and have all their parts developed in conformity with the functions allotted to them. The parts of the flower, on the other hand, are concerned in the function of reproduction, and in their structure and development are fitted for the office which they have to perform. The parts of the flower originate in the same way as the leaves, in the form of simple cellular projections from the axis. The appearances which they afterwards present depend on organogenic (organ-producing) laws of development—the arrangement of the cells and vessels, and their contents, being modified in each special organ.

The leaf is considered as the Type of all. This idea was started by Linnæus, and was afterwards more fully brought forward by Goethe. In speaking of the parts of the flower... Botany, as metamorphosed or modified leaves, it must not be supposed that we mean that these parts have, at any period of their existence, been true leaves. All that is implied in the statement is, that both are formed on the same general plan, that both are arranged upon the same principle, and that one law pervades their morphology. The cell from which the leaf is formed is no doubt very different as regards the organogenic law impressed upon it from the cell which gives rise to a sepal, a petal, a stamen, or a carpel. Nevertheless, when we examine the parts scientifically, we perceive certain homologies in form and structure belonging to the one set of organs which are represented in the other. This morphological view of the organs of the flower associates them with the leaves in a very interesting manner, and enables us to give a philosophical exposition of the harmonies subsisting between them.

In passing from leaves to flowers, there are certain intermediate organs called bracts, which are merely altered or modified leaves, producing flower-buds at the part where they emerge from the stem. From these we proceed to the flower-stalks, which are branches bearing flower-buds in place of leaf-buds. The outer whorl of the flower has generally more or less of the appearance and colour of leaves, and, in many instances, the leaflets produced on the flower-stalk pass by insensible gradations into sepals. Between sepals and petals there are transition forms, as seen in the White Water-Lily, the Magnolia, and many plants where the colour of both is similar. The petals, in their turn, sometimes become narrowed and altered, so as to pass into stamens, as in the White Water-Lily, where it is scarcely possible to say where the different whorls end. It is very rare to find the stamens passing into the pistil. In the case of monstrousities, however, produced by cultivation, the pistil undergoes such changes as to prove that it is formed on the same type as the rest. Occasionally all the parts of a flower, as in some monstrous specimens of Dutch Clover, are converted into leaves.

When sepals are changed into petals, petals into stamens, or the latter into carpels, the alterations are said to be in the ascending series, and it is called a case of ascending or progressive metamorphosis. By cultivation, and other causes, this series of phenomena is sometimes reversed. Thus, in the double cherry, the pistil is frequently altered, so as to appear in the form of one or more leaves (Fig. 186, a and b); and in double flowers the stamens are changed more or less completely into petals. In Figure 187 is exhibited

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**Fig. 186.**

The carpel of the double-flowering Cherry. In this plant the fruit is abortive, and in its place one or more leaves are produced. The carpellary leaf is either expanded, a, or folded, b. This shows that the fruit of the Cherry is formed in the same type as the leaf.

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**Fig. 187.**

Diagrammatic representation of the Rose. The stamen, c, is altered gradually, passing through the states represented at 2, 4, and 6 until it becomes a complete petal, 2, and the petal at 1 becomes a stamen. The diagram shows the origin of a stamen with a strongly marked midrib prolonged beyond the apex.

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**Fig. 188.**

An ideal representation of a flower arising from a bud, b, and formed by a single sepal, c, a single petal, p, a single stamen, s, and a single carpel, f; the parts being alternate, and separated by internodes.

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**Fig. 189.**

Diagrammatic section of a symmetrical pentamerous flower of Stonecrop (Sedum). The diagram shows five stamens, ten stamens alternating with the sepals, ten stamens in two rows, and five carpels containing seeds. The dark lines on the outside of the carpels are glands.

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Figure 190 there is a section of a symmetrical flower of Stone-crop, with five sepals, five alternating petals, ten stamens in two rows, and five carpels. Figure 191 shows a flower of Heath, with four divisions of the calyx and corolla, eight stamens in two rows, and four divisions of the pistil. In Figure 192 there are three divisions of the calyx, corolla, and pistil, and six stamens in two rows. In all these cases the flower is symmetrical. Flowers in which the number of parts in each whorl is the same are Isomerous (isos, equal, and μέρος, a part); when the number in some of the whorls is different, the flower is Anisomerous (ανίσως, unequal). When the parts of any whorl are not equal to, or some multiple of the others, then the flower is Unsymmetrical. This is seen in Veronica as given in Figure 193, where there are four divisions of the calyx, four of the corolla, and only two stamens, and two parts of the pistil.

Symmetry, then, in botanical language, has reference to a certain definite numerical relation of parts. A flower in which the parts are arranged in twos is called Dimerous (διά, twice, and μέρος, a part), the symmetry being Binary, and the arrangement marked thus $V$. When the parts of the floral whorls are three, the flower is Trimerous (τρίς, thrice), and the symmetry being Ternary or Trigonal, is marked $V$. When the floral pieces are in a series of four, the flower is Tetramerous (τετρά, four times), its symmetry being Quadrinary, and marked $V$. A Pentamerous (πέντε, five) flower, marked $V$, has Quinary or Pentagonal symmetry. The symmetry which is most commonly met with in the vegetable kingdom is trimerous and pentamerous—the former occurring generally among Monocotyledons, the latter among Dicotyledons. Tetramerous symmetry occurs also among Dicotyledonous plants, and the numbers 2 and 4 prevail in the reproductive organs of Acotyledons.

The parts of the flower are, generally speaking, arranged so that those of one whorl are alternate with those of the next whorl. Thus, the petals alternate with the sepals, and the stamens with the petals. When the numbers in any series, such as the stamens, are multiplied, and the flower is still symmetrical, then the organ is found to consist of a definite number of whorls alternating with each other. Thus, in diagram 192, the stamens are six in place of three, and they are arranged in two alternating whorls—the parts of the outer whorl alternating with the petals, and with those of the inner series. The pistilline whorl is more liable to changes than the other parts of the flower. It frequently happens, that when it is fully formed, the number of its parts is not in conformity with that of the other whorls. In such circumstances, however, a flower is still called symmetrical, provided the parts of the other whorls are normal.

The various parts of the flower have a certain definite relation to the axis. The terms superior and inferior have reference to their position. Thus, in axillary tetramerous flowers (Fig. 191) one sepal is next the axis, and is called superior or posterior; another next the bract, is inferior or anterior, and the other two are lateral; the petals (when present) being alternate with the sepals, are so placed, that two are posterior, and two anterior; while the four stamens are arranged like the sepals. In a pentamerous flower it happens, that either one sepal is superior, two inferior, and two lateral, as in the calyx of Rosaceae (Fig. 194); or two are superior, one inferior, and two lateral, as in the calyx of Leguminoseae (Fig. 195). The reverse, of course, by the law of alternation, is the case with the petals.

A flower normally consists of four whorls, calyx, corolla, stamens, and pistil, and when these are all present, the flower is complete. When each whorl consists of the same number of parts, or of a multiple of the parts, successively alternating with one another, we have seen that the flower is symmetrical. When the different parts of each whorl are alike in size and shape, the flower is regular. The absence of any of the whorls renders the flower incomplete. Want of correspondence in the number of the parts of the whorls causes want of symmetry, as has been already shown, while differences in the size and shape of the parts of a whorl makes the flower irregular, as in the papilionaceous flower represented in Figure 195.

In their earliest stage of development all the parts of the floral whorls are regular and symmetrical, consisting of similar minute cellular papillae arising from the axis. The alterations in their regularity and symmetry depend on changes taking place during their growth. These alterations are traced to the adhesion of one part to another, the union of different whorls, irregular growth, complete suppression of one or more parts or whorls, degeneration or degradation, multiplication of parts, and chorisis or deduplication.

A flower becomes incomplete by the non-development, or by the transformation of one or more whorls. It becomes irregular by one or more parts of a whorl being enlarged or diminished in size, and by irregular cohesions; and it becomes unsymmetrical when some of the parts of one or more whorls are suppressed, so that their numerical relations do not correspond. The consideration of all the changes which the parts of plants undergo, or, in other words, the permanent deviations from what may be considered as their normal state, is included under the term Teratology (τεράτων, a monster, and λόγος, discourse). Every alteration in the organs of the flower may be traced to the morphological laws to which we have already alluded. In treating of the separate floral whorls, notice will be taken of the changes which they undergo; in the meantime some general remarks will be made on the causes to which these changes are referred.

Union or adhesion of the floral whorls, or of the parts composing them, gives rise to various changes in form and symmetry. The adhesion is sometimes very irregular, so that certain parts are more completely united than others. Many forms of irregular flowers are due to this cause. The non- development of whorls gives incompleteness to the flower. The absence of the corolline whorl renders a flower Apetalous or Monochlamydeous, the absence of both the calyxine and corolline whorl makes the flower Naked or Achaemydeous. The suppression of the stamens, or of the pistil, renders the flowers Uniseriate. The non-appearance of a whorl deranges the relation of the different parts, and destroys their alternation. Thus, in the apetalous flower of the Nettle, the stamens, in place of being alternate with the whorl on their outside, are opposite to it, and this relation of parts leads to the detection of the suppressed whorl.

Various parts of the flower are apt to become abnormal, or degenerate by Transformations of different kinds. Some of the parts may be converted into scales or into hairs. The floral leaves of the catkin of the Willow, and those of the Hop, are membranous scales, while those of the Cone are hard scales; the Wig-tree (Fig. 158) produces hairs instead of flowers on some of its peduncles, and the calyx of the Dandelion, and other compound flowers, assumes the form of hairs, which remain attached to the fruit. In double flowers the stamens and pistils degenerate by being converted into petals.

Sometimes the parts of a flower are increased in number by the growth of additional parts, or by the splitting of organs during their development. This latter process is called Choris (separation), and seems to account satisfactorily for the appearance of certain anomalous parts which do not follow the law of alternation. This choris consists in the formation of two parts out of one, the separated parts being either placed one in front of the other by transverse choris, or side by side by collateral choris. The lamina of a petal may be split in such a way that a scale is produced on part of it, as seen in Lychinis. Stamens may be divided so that two standing collaterally are produced in place of one; in this way some account for the abnormal state of the stamens in cruciferous flowers, such as Stock and Wallflower. In these plants, while the calyx and corolla consist of four parts, the stamens are six (Fig. 177), owing, it is said, to collateral choris of two of them. The flowers are thus considered normally tetramerous. In the Fumitory there are two sepals, four petals in two rows, and six stamens. The latter consist of two perfect stamens, and four incomplete, which are considered as being produced by collateral choris of two stamens. In this way the flower would be normally dimerous. When the parts of contiguous floral whorls are opposite to each other, in place of being alternate, the occurrence may be accounted for, either by suppression of a whorl, or by choris.

b. The Flower-Bud.

The various parts of the flower, consisting of the floral envelopes and the essential organs of reproduction, are contained in the flower-bud. They appear at first in the form of small cellular mammillae, or prominences, the parts of each verticil being equal and separate. In their development (organogeny) they follow the same order as leaves—the extremities of each of the parts being first formed, and irregularities, caused by adhesion and other causes, occurring only during the progress of growth. In general the whorls are developed successively, from the calyx to the pistil; but, in some instances, the petals are retarded in their growth, so that the stamens are completed before them.

The terms Profloration (pre, before, and flo, flower) and Astivation (extives, pertaining to summer) are used to express the arrangement of the different parts of the flower in the flower-bud. The relation of these parts to each other is similar to that which occurs in the leaf-bud, and which has been considered under profloration. The same terms are also used to express the nature of many of these arrangements. As regards each leaf of the flower, it is either spread out, as the sepals in the bud of the Lime-tree; or folded upon itself (conduplicate), as in the petals of some species of Lysimachia; or slightly folded inwards or outwards at the edges, as in the calyx of some species of Clematis, and of some herbaceous plants; or rolled up at the edges (involute or revolute); or corrugated and crumpled, as the petals of the Poppy.*

*Plate CXXIV. fig. 2.

The position of the parts of the flower relative to each other, in the bud, gives origin to the terms valvar, contortive or twisted, and imbricated. In the first two the parts are placed at the same level, in a circular manner, while in the latter they are at different heights, and follow a distinctly spiral order. The astivation is Valvar, or the parts are arranged in a valvate manner (Fig. 196), when they are so applied as to be in contact at their edges without any folding. They are in a circular verticil. When the parts of the verticil are slightly folded inwards at their edges the astivation is Induplicative (Fig. 197), when folded outwards Reduplicative (Fig. 198). When the parts of the corolla are united they are occasionally folded in a plaited manner.

In Contortive astivation the parts are in a circle, or apparently so, and one edge of each is directed inwards, so as to be overlapped by the contiguous part, while the other edge covers the margin of the part adjacent on the other side; each part also is, as it were, twisted on its axis, and the whole whorl exhibits a convolute appearance (Fig. 199). It is well seen in the unexpanded petals of Malvaceous plants,* in the corolla of Cyclamen, and in that of many Apocynaceae, which were called Contortae by old authors.

The astivation called Imbricated or Imbricative embraces those bud arrangements in which the parts are placed at different heights so as to overlie each other, and form a more or less evident spiral cycle (Fig. 200). When the parts of a floral whorl are five, as is the case in many Exogens, it is often found that there are two parts wholly on the outside, two completely internal, and one intermediate, overlapped at one edge by one of the outer parts, whilst its other edge covers one of the inner parts (Fig. 201). This is Quincuncial or Spiral imbrication, and is the normal arrangement in pentamerous flowers, corresponding with the arrangement in leaves. In personate flowers, as Frogmouth, a variety of imbricated astivation occurs, called Cochlear, in which the second part of the cycle, in place of being external (as in the ordinary quincuncial arrangement), becomes wholly internal. When imbricated astivation occurs in trimerous flowers, there is one part outside, one inside, and one intermediate, the arrangement being 3, as in leaves. When the flower is tetramerous, there are two outer parts and two inner parts; this being analogous to what occurs in opposite decussating leaves. In pea-like

*Plate CXLII. Botany. blossoms it is usual to find a modification of imbricated

Fig. 200. Diagram to illustrate imbricative or imbricated nativation, in which the parts are arranged in a spiral cycle, following the order indicated by the figures 1, 2, 3, 4, 5.

Fig. 201. Diagram of a papilionaceous flower showing vexillary nativation, in which the parts of the flower are arranged in a spiral cycle, so that 1 and 2 are wholly external, 3 and 4 are internal, and 5 is partly external and partly internal.

Fig. 202. Diagram of a papilionaceous flower, showing vexillary nativation, 1 and 2 are also external, but 3 is partly internal, while 4 is a calyx or corolla, which, in place of being internal, as marked by the dotted line, becomes external, 5 the remaining part of the keel.

The order of the sepals is indicated by the figures.

nativation, called Vexillary, in which the large petal called the vexillum, and which is superior or next the axis, overlaps the rest (Fig. 202). In some instances, as in the Judas-tree, the vexillum is included between the lateral petals (ale), as represented by the dotted lines, Figure 202.

The different verticils of the flower have not always the same nativation. In the Mallow tribe the calyx is valvate, while the corolla is twisted; in St John's Wort the calyx is imbricated and the corolla twisted; in the Rock-rose the three inner sepals are twisted in one direction, while the petals are twisted in an opposite direction.

c. The Floral Envelopes.

* The Calyx or Outer Floral Envelope.

The Calyx is the outer floral envelope, and is composed of a whorl of leaves called Sepals. These leaves have usually the structure and appearance of ordinary leaves, as regards the distribution of their cells and vessels. They are frequently of a greenish hue, having chlorophyll in their cells, and stomata on their lower (outer) epidermal covering. When not green the calyx is said to be coloured, as in Columbine, Monkshood, Larkspur, Fuchsia, and Indian cress. It is not common to find the individual sepals divided. Sepals are usually sessile leaves, having no stalks. They are either distinct from each other, as in Wallflower, or they are combined, as in the Melon. When the sepals are of the same size and form, the calyx is regular, when not so it is irregular.

When the sepals are separate the calyx is Polysepalous, Polyphyllous, or Dialysepalous (πολύς, many, ἐσχάτων, to separate), the number of sepals being marked by the Greek numerals prefixed. Thus, discapalous means a calyx with two distinct sepals; trisepalous with three; tetrasepalous with four; pentasepalous with five; hexasepalous with six; or the Greek word phyllia, meaning leaves, is used, and a discapalous calyx is denominated diphylous, and so on. When sepals are united by adhesion, they form a Gamosepalous or Gamophyllous (γάμος, union) calyx (Fig. 203), terms implying union of sepals or leaves, and therefore preferable to monosepalous and monophyllous, which mean literally one sepal or leaf. This adhesion of sepals varies in extent, and thus gives rise to the terms entire, when the union is complete, and there are no divisions at the top, toothed, cleft, and partite, when the divisions are mere toothings, or extend to the middle, or to near the base. Thus, a gamosepalous calyx (Fig. 203), may be five-toothed (quinque-dentate), five-cleft (quinquefied), or five-partite (quinque-partite), the number of divisions usually indicating the number of sepals of which the calyx is composed. In an entire gamosepalous calyx the venation assists in the determination of the number of sepals.

When the union of the sepals is not equal in all the parts, the calyx has an irregular form, as in Labiate flowers (Fig. 204). In the latter case the calyx is two-lipped (bilabiate), the upper lip being composed of three sepals, one of which is either arched or stands out from the rest in a marked manner, and the lower lip being formed of two sepals. The united parts of a gamosepalous calyx form the tube, the free portions at the apex are the lobes or segments of the limb, and the orifice of the tube is the throat (fauc).

The tube of a gamosepalous calyx frequently adheres more or less completely to the other whorls, especially to the pistil. In the latter instance the calyx remains persistent, and forms part of the fruit, as in the Gooseberry. In such instances the limb of the calyx often becomes degenerate, and is either absent, or appears in the form of scales or pointed projections, or of a circular rim (Fig. 205), or of pappus, as in Composite flowers (Fig. 206). In the adherent calyx of Valerian, the limb is at first a ring, but ultimately expands in the form of hairs, and hence is called pappose.

The calyx may continue persistent, and yet be separable from the fruit, as in Hembane,* and in the Peruvian Winter-cherry and other species of Physalis (Fig. 207), where it increases after the flower has withered, and surrounds the fruit like a bladder. It sometimes continues in a withered state, as in the Heath, and is called marcescent. The term superior is applied to the calyx or perianth when it is so united to the fruit as to appear to arise from its summit, as in Melon, and Iris. In the Rose (Fig. 185) the tube of the calyx bears numerous carpels on its concave surface, and the limb at the summit is divided into five segments.

In place of being persistent, the calyx is frequently deciduous, falling off immediately after the flower expands, as in Crowfoot. In the Poppy* (Fig. 208) the two sepals are detached before the anthesis or the opening of the flower, and they are said to be caducous. In Eschscholtzia,* the calyx is composed of sepals united together, and joined by an articulation to the thalamus; as the flower expands, they give way at the joint, and fall off in the form of a candle-extinguisher. By the irregular development of one or more sepals, the spurred (calcarate) calyx of Larkspur and of Indian Cress is produced, as well as the hooded or helmet-shaped (galeate) calyx of Monkshood. In Grasses and Rushes the perianth Botany assumes a glumaceous or scaly appearance. It is very rare to find the calyx wholly absent. This, however, occurs in some of the Euphorbias,* in which the flowers are naked (achlamydeous), as shown in Figure 200. In these plants there is a series of bracts which at first sight appear to be the calyx; but they are really an involucre inclosing several distinct flowers (Fig. 210). In the Strawberry, Potentilla, and Mallow, the calyx consists of two alternating whorls, the exterior of which has been called Epicalyx, and is by some considered a row of bracts. An epicalyx is also seen in the Carnation. When there is only one floral envelope present, as in Goosefoot (Fig. 178), it belongs to the calycine whorl, whatever may be its form or colour.

† The Corolla or Inner Floral Envelope.

The Corolla is the inner envelope of the flower, and is composed of a whorl of leaves called Petals (pétales, a lamina or leaf), which alternate with the sepals, as seen in Figure 173, and are frequently equal to them in number (isomeres), or some multiple of them. The petals differ from the sepals in being rarely green. They usually exhibit showy colours, and are often odoriferous. Structurally they are composed of cellular and vascular tissue, the latter being spiral vessels and delicate tubes. The epidermis of petals does not in general exhibit stomata, but it sometimes displays beautiful hexagonal and radiating markings under the microscope. It is usually smooth (glabrous), but occasionally coloured hairs occur on it, as in the Bogbean. Petals originate in cellular projections, which are either connected by a ring of cellular tissue, or are separate, according as the parts are ultimately to be united, or to remain distinct. Even when the petals become irregular in after growth, they are equal in the first instance. Some petals continue to increase in size after the flower has expanded.

The forms of petals vary. Sometimes they resemble sessile coloured leaves, as in Crowfoot (Fig. 211); at other times they are separated into two portions, as in the Wallflower (Fig. 212), one narrow, c, forming the claw, and the other broad, l, constituting the limb or lamina. Petals being like leaves, exhibit varieties in their outline or circumscriptioin. In some plants they are split at the apex, so as to be bifid or trifid, or cut into numerous segments (Fig. 213). When a small portion of their apex is deficient they become emarginate and obcordate, and when lobed at the base they are cordate. The apex of petals is sometimes prolonged in the form of a narrow thread, as in Strophanthus, or it ends in a point, which is either straight or inflexed, as in Umbelliferous plants.* Some petals are folded, *Pl. CXXI., so as to assume a tubular or pitcher-like form, as in the fig. 1, Hellebore* (Fig. 214), a spurred form, as in Columbine *Pl. CX. (Fig. 215), Violet, and Larkspur, a gibbous form, as in Fumitory, or a horn-like aspect, as in the petals under the helmet-shaped sepals of Monkshood (Fig. 216). These anomalous petals sometimes assume a normal form, as in a variety of Columbine, in which the spurs disappear.

When the petals are separate (free and distinct) the corolla is Polypetalous or Dialypetalous (woxis, many, and xélos, to separate), and the number of the petals is indicated by prefixing the Greek numerals to the term petalos, in the same way as in the case of the sepals; thus, in Figure 217, the corolla is pentapetalous. In the Vine (Fig. 218), in which the corolla is polypetalous, the petals in their early state are united together by their rapices, and afterwards separate and fall off. When the petals are united, the corolla is Gamopetalous or Monopetalous (yayos, marriage or union, pétaos, one), and the number of its parts is marked by the venation, or by the divisions of the apex, just as in the case of the calyx. Thus, in Figure 219, the corolla consists of five petals united, their number being ascertained by the lobes at the apex, as well as by the midribs. The united portion is called the tube, the divisions are called lobes, and the orifice is the throat (faux). The term limb is often given to the expanded and free part of a gamopetalous corolla.

Some varieties of polypetalous corollas deserve notice. Of the regular forms may be mentioned the roseaceous, as in the Rose and the Strawberry (Fig. 220), in which there are spreading petals, without claws or with very short Botany.

claws; the *liliaceous*, where the petals gradually taper from the apex to the base, as in the Lily; *caryophyllaceous*, where the petals have long, narrow, tapering claws, inclosed in the calyx, as in the Carnation and Pink; *cruciferous* or *cruciate*, in which there are four petals, usually with claws (Fig. 212) and arranged in the form of a cross, as in Wallflower (Fig. 176).

Among the *irregular* forms of polypetalous corollas we may notice the *papilionaceous* (butterfly-shaped) corolla, as seen in the Pea (Fig. 221), consisting of five parts, differing in size and shape, the upper, *st.*, called the *standard* (vexillum), the lower, *car.*, called the *keel* (carina), formed of two partially-united petals, and the two lateral, *a*, called *wings* (alae). These parts are separately represented in Figure 222, *a* being the vexillum, *b* the carina, and *c* one of the alae.

In Monocotyledonous plants the coloured perianths are often polyphyllous, and there is a peculiar irregular kind which is met with among Orchids. It may be called the Orchidaceous perianth, and consists of six parts, one of which, called the *Labellum*, presents many remarkable forms. It is shown in Figure 223, which represents an Orchis, with its labellum, *l*, and a spur, *s*. The labellum varies much in form. In Cypripedium it is hollow, like a slipper, and is called *calceolate*.

Gamopetalous corollas are also divided into regular and irregular forms. In the former the parts are equal in size and equally united, while in the latter they are unequal in these respects. Regular forms are bell-shaped (campanulate), that is, shaped like a bell, and swelling out regularly from base to apex, as in the Harebell (Fig. 219); funnel-shaped (infundibuliform), in which the tube is narrow below, and expands towards the summit, as in Tobacco (Fig. 224); tubular, or nearly uniformly cylindrical, as in some composite flowers; salver-shaped (hypocrateriform), when the limb or lobed portion spreads out at right angles to the tube, which is long, as in Auricula and Primrose; and wheel-shaped (rotate), when a salver-shaped corolla has a very short tube, as in Forget-me-not (Fig. 225). There are also intermediate forms, as in Comfrey, in which the corolla is campanulate-tubular, presenting a combination of the bell-shaped and tubular forms.

Irregular gamopetalous corollas are seen in the tipped (labiate and bilabiata) forms (Fig. 173), in which the union of the petals takes place in such a way as to produce an upper and lower portion, with a gap (hiatus) between them, like the mouth of an animal (Fig. 226). The upper lip is usually composed of two petals, the lower of three. The same form is met with in the calyx (Fig. 204), but the number of parts in the lips is reversed. A labiate corolla or calyx, with the upper lip much arched, like a helmet (galea), is said to be ringent (Fig. 226). Sometimes the upper lip is very short and nearly wanting, as in Bugle. When the lower lip is approximated to the upper, so as to leave only a chink (ricus), with a projecting portion below it, called the palate, the corolla is denominated masked (personate), as seen in Frogmouth (Fig. 227). In Calceolaria there is a peculiar irregular corolla with two hollow lips. When a tubular corolla is split down on one side (Fig. 228), as in the florets of the... Botany.

Dandelion," and in the white florets of the Daisy, it is called strap-shaped (ligulate).

The lower part of some gamopetalous corollas, such as Valerian and Frogmouth (Fig. 227 b), projects in the form of a bag or sac, and is called saccate or gibbosus. Sometimes the projecting part assumes the form of a spur (calcar), as in Red Valerian, and Snapdragon (Fig. 229). In some gamopetalous corollas there is a very slight irregularity of form. Thus, in Digitalis® the corolla has a somewhat campanulate form, but its development is not equal; the Speedwell (Fig. 230) has a form nearly rotate, but the lobes are unequal; the Bugloss has a funnel-shaped corolla with a curved tube.

In some gamopetalous corollas with a single spur, it happens occasionally, that what are called Pelorian varieties occur in which five spurs are produced. This occurs in common Snapdragon frequently, as well as in species of Frogs-mouth.

In Grasses and Sedges the arrangement of the parts of the flower is peculiar. In place of verticillate leaves forming the flower, there are alternate scales or glumes. The flowers of grasses usually occur in spikelets® (Fig. 165), which consist of one or two glumes, covering several flowers, having the form represented in Figure 231, and inclosing flowers which are composed of scales (pales or glumella), delineated in Figures 232 and 233—the former being the outer, and the latter the inner pale or glumella, which are placed at different heights in an alternate manner. In the flower of the Oat (Fig. 234), after removing the outer pale or glumella, the inner one, ps, is seen with two scales (lodiculae or squamae), sq, at the base, inclosing the essential organs of reproduction. In Carices the male flowers are borne on scales, and so are the female, as shown in Figure 235, in which the scale, s, is placed on one side. Within the scale the female flower is situated, having a peculiar bag-like covering, u, termed perigynium.

Abnormalities in the Corolline Whorl.—The parts of the corolla are frequently adherent to those of the calyx, and any change taking place in the latter also causes an alteration in the former. Some of the petals are occasionally suppressed, and sometimes the entire corolla is wanting. The latter occurs normally in apetalous monocotyledonous flowers, such as Chenopodium (Fig. 178); and it also occurs accidentally. Petals, which are in general coloured, sometimes become green. A corolla, normally gamopetalous, is sometimes divided into separate petals. Flowers become double by the multiplication of the parts of the corolline whorl. This arises in general from a metamorphosis of the stamens. Union of separate flowers (synanthos, ovir together, and ἀνάστασις, flower) occasionally occurs, and the adhesion which thus takes place causes various changes in the whorls.

Connected with the inner surface of the petals, there are placed occasionally appendages in the form of scales® or filamentous processes. These are considered as being modified petals, and they are usually traced to transverse chorisis, in consequence of their being placed opposite to the petals. In many of the Borage order, such as the Comfrey (Fig. 236), Forget-me-not (Fig. 225 b), as well as in the Chickweed tribe, and in the Crowfoot (Fig. 211), petaline scales or lamellae of this nature are observed, which, like many other processes connected with the flower, received, in the days of Linnaeus, the name of Nectaries. Peculiar changes in an inner row of petals and in the stamens may also give rise to corolline appendages, as, for instance, the beautiful fringes of the Passion-flower, the crown of the Narcissus (Fig. 149), and the glandular scales of the grass of Parnassus (Fig. 237).

d. Essential Reproductive Organs.

These organs constitute the inner whorls (verticils), and originate, like the floral envelopes, from the thalamus or torus (the upper part of the axis or peduncle), in the form of minute cellular processes. In their development they resemble leaves, but in general they differ much more in their appearance from the leaves than the floral envelopes do. The essential organs are the stamens and pistil, as shown in Figure 238, where there are five stamens arising from the thalamus, and surrounding one pistil. The stamens constitute the Androecium, and the pistil the Gynoecium.

These organs are necessary to form a perfect flower, and without them no seed is produced in flowering plants. When, by cultivation, they are changed into floral envelopes, the flower cannot perform its proper functions. These organs are not, however, always present in every flower. When both are present in the same flower, it is Bisexual, Hermaphrodite, or Monoclinous (μονόκλινος, one, and κλίνω, bed), and is marked Φ. When one of the organs only is present, the flower is Unisexual or Diclinous, and is marked Φ Φ; being called Staminate, male or sterile, when the stamens alone are developed, as indicated by the mark Φ; and Pistillate, female or fertile, when the pistil only is produced, as indicated by the mark Φ. Unisexual Plants, such as the... Hazel and Arum (Fig. 166), in which the staminiferous and pistilliferous flowers are on the same individual, are denominated Monoeious (ποικιλος, and δοξαν, habitation), and are marked δ—♀; unisexual plants, such as the Willow and Hemp, in which the staminiferous and pistilliferous flowers are on separate individuals, are denominated Dioecious (δοξαν, twice, and δοξαν, habitation), and are marked δ♂♀. In the case of Palms it often happens that, while some flowers are staminate and others pistillate, there are others which are perfect or hermaphrodite; on this account such plants are called Polygamious (πολυς, many, and γαμος, marriage), and are marked δ♂♀♂♀. In all cases in which one of the whorls of the essential organs is absent, it is considered as depending on suppression or non-development; and this view is confirmed by the fact that, in many unisexual flowers, the rudiments of the suppressed organ may be seen, and that in certain circumstances it is developed.

*Androecium or Staminal Organs.*

The stamens are placed immediately within the petals. When there is one whorl the stamens are usually equal in number to the petals, and alternate with them (Fig. 175). When the stamens are twice as many as the petals, they are in two whorls, alternating with each other (Figs. 191 and 192). When there are more than two whorls, each successive verticil alternates with that preceding it. When, in place of being alternate with the petals, the stamens are opposite to them, as in the Primrose, the abnormality is considered as depending, either on the suppression of an outer row, or on transverse chorisis of the petals, or vertical chorisis and union of the stamens.

In cases in which the stamens are not equal in number to the petals, the abnormality may be traced to suppression of a certain number, to abortion, adhesion, or chorisis. In Cruciferous plants there are four sepals, four petals, and six stamens, four of which are longer than the others (Fig. 177). It is supposed that in this case each pair of long stamens is in reality one which has been split by lateral chorisis. This is confirmed by finding teeth only on one side of the filaments of these stamens, while in the two shorter ones teeth exist on both sides, and also by the fact that partial adhesions between them are sometimes seen, as in Streptanthus, and that some cruciferous plants have only four stamens.

A perfect stamen consists of two parts, the Filament (Fig. 239, f), representing the petiole of the leaf, and the Anther (Fig. 239, a) analogous to the blade, containing minute cells, in the form of Pollen (Fig. 239, pp). The filament, like the petiole, is sometimes wanting, and the anther is then sessile. The filament is usually articulated to the thalamus, so that the stamen falls off after performing its functions; but in some instances it is persistent and not articulated.

In the filament cellular tissue exists in a condensed form, surrounding a central bundle of spiral vessels, which represents the fibro-vascular system of the petiole. It has a thin epidermal covering, which sometimes presents stomata. Cellular prolongations also occur in the form of hairs, as in the Virginian Spiderwort (Tradescantia), Anthicum, and Verbascum, where the stamens are called stypose, and in Anagallis tenella, where the hairs have a beautiful knobbed appearance.

The anther, like the lamina of the leaf, is developed before its stalk. It consists originally of a cellular mammilla, containing a mass of thin-walled cells (Fig. 240, ee and ef). In the progress of growth larger cells are produced in the interior (Figs. 241 and 242, cm), forming four separate clusters, each of which is surrounded by a special cellular covering (Fig. 242, ef). These larger cells are destined for the formation of pollen, and the four places at which their development commences may be seen on a transverse section of a very young anther. These clusters of pollen cells increase in size, and gradually cause absorption of the surrounding parenchyma. It generally happens that two of the adjacent clusters of pollen cells unite by obliteration of their special covering at one side, and thus ultimately two pollen cavities are found in the anther, in place of four.

In its fully developed state, the anther presents two lobes (Fig. 239, b), like the two halves of the blade of the leaf; these lobes being united by a partition, called the Connective (Fig. 239, g), representing the midrib, and consisting of cells and spiral vessels. Each anther lobe has one or two cavities, which are receptacles of the cellular grains of pollen. These cavities correspond to the large cells seen in Figure 242, cm, with their special covering, ef, which forms the inner lining of the anther case, called Endothecium (εσωτερος, within, θυρος, a box or loculeum). This lining exhibits elastic spiral fibres, which probably assist in bursting the outer epidermal covering of the anther called Exothecium (εξωτερος, without), corresponding to the cells marked ce in Figures 241 and 242. In the cells of the endothecium, as the anther approaches to maturity, the membrane becomes sometimes obliterated, so that the delicate fibres alone are left, as is seen in the Melon (Fig. 243), and in Cobra. These spiral fibres appear also to fill up the space between the two coverings in many full-grown anthers.

Thus the anther represents the lamina of a leaf, with its two halves divided by a midrib, surrounded with a double epidermal covering, the inner being fibro-cellular, and containing cellular tissue which assumes the form of pollen. When there are four cavities (loculi or thecae as they are called) in the anther, they may be considered as represent- ing the two halves of the leaf, each with its upper and lower stratum of cells. This division into four is seen in the young state of anthers, and is considered as the normal state. When it remains in the fully developed anthers they are called quadrilocular or tetrathecal (Fig. 244). When, owing to obliteration of some of the partitions, only two loculi remain, as is very generally the case, the anther is bilocular or dithecal (Fig. 239 a).

It happens occasionally that, by the suppression of one lobe, as in Gomphrena, or by the disappearance of the partition between the two lobes, the anther becomes dimidiate, or one-celled. In the Mallow tribe the divergence of the base of the anther lobes, and their complete union at the apex, render them one-celled (unilocular, monothecal); while in Labiate plants, by the turning of one of the lobes, a union takes place by their bases, so that they form one cavity. The long connective of the Sage and other species of Salvia separates the anther lobes, so that each appears a monothecal anther (Fig. 245), one of which, \(a\), contains pollen, while the other, \(b\), is abortive.

The stamens vary in number, and names are given to flowers accordingly. Thus,

1. stamen is Monandrous (\(μόνος\), one, and \(\alphaνθός\), male or stamen), Hippuris. 2. stamens is Diandrous (\(διά\), two), Veronica. 3. stamens is Triandrous (\(τρία\), three), Grasses. 4. stamens is Tetrandrous (\(τετρά\), four), Alchemilla. 5. stamens is Pentandrous (\(πέντε\), five), Primula. 6. stamens is Hexandrous (\(ξήξ\), six), Tulip. 7. stamens is Heptandrous (\(ἑπτά\), seven), Trientalis. 8. stamens is Octandrous (\(ὀκτώ\), eight), Heath. 9. stamens is Enneandrous (\(ἐννέα\), nine), Butomus. 10. stamens is Decandrous (\(δέκα\), ten), Saxifrage. 11. stamens is Dodecandrous (\(δώδεκα\), twelve), Asarum. 20. stamens is Icosandrous (\(ικοσ\), twenty), Strawberry.

Numerous and indefinite stamens is Polyandrous (\(πολύ\), many), Poppy.

In the common Marc's-tail there is only one stamen in each flower, while in Cereus nycticalus 400 have been counted. The number of the stamens determines some of the classes in the Linnaean artificial system of classification.

In the case of Euphorbia, flowers are met with, consisting of a single stamen (Fig. 246), and others consisting of a single pistil. These, when inclosed in one common involucre, or bracteal envelope (Fig. 247, i), seem to be stamens and pistils in the same flower. But on examination it is seen that a joint occurs at a part of the supposed filament (Fig. 246, a), indicating its connection with the peduncle, \(p\), and so also in the case of the pistil. In some of the species of Euphorbia a proper floral envelope appears at the joint indicating the true nature of the organ. The flowers represented in Figure 247 are therefore naked or achlamydeous male and female flowers on one plant, which is therefore said to be monocrous.

The position of the stamens is normally within the petals, and outside the pistil. They arise from the part of the peduncle below the latter, and hence they are Hypogynous, which means under the pistil (\(ὑπό\), under, and \(\γυνή\), female or pistil). But, as in all other parts of the flower, adhesions take place by which changes in apparent position are produced. Thus the stamens, in place of being free and truly hypogynous, sometimes adhere to the tube of the calyx, becoming Perigynous (\(περί\), around), which means surrounding the pistil; while at other times they adhere completely to the ovary, and appear to arise from the top of it, and are hence called Epigynous (\(ἐπί\), upon). When the stamens adhere still more completely to the pistil, the union extending above the ovary, they become Gynandrous (\(γυνή\), female, and \(\ανθός\), male), as in Orchis, and in Birthwort (Fig. 248), and form with the pistil a column in the centre of the flower.

In place of adhering to the contiguous organs, the stamens may be distinct from them, but united to each other either by their anthers or by their filaments. When the filaments are combined into one mass, more or less completely, the flowers are Monadelphous (\(μόνος\), one, and \(\δάλφις\), brother), as in the Mallow (Fig. 249); when in two sets or bundles they are Diadelphous, as in Fumitory, and in some papilionaceous flowers, in which the bundles are often unequal, nine stamens being united in one set, and only one (which is superior) in the other (Fig. 250); when in three sets they are Triadelphous, as in St John's Wort; and when in more sets Polyadelphous, as in the Castor-oil plant (Fig. 251). The numerous stamens in the Mallow and St John's Wort, and Castor-oil plant, are by some traced to collateral chorisis, or repeated divisions of the stamens. Sometimes the filaments are united by means of an interposed membrane (a sort of crown), as in the Pancratium. When the stamens are united by their anthers, the flowers are termed Syngenesious or Symantherous (\(συν\), together, \(\γυνή\), origin, \(\ανθός\), anther), as in Composite (Fig. 252), in Violet, and in Lobelia.

Stamens are often shorter than the corolla, and are then said to be included; but at times they elongate and extend beyond it, when they are exserted. In some flowers we find certain stamens constantly longer than others. Thus, in many Labiate flowers (Fig. 253), and in Frogmouth, we meet with two long and two short stamens, the flowers being Didynamous (\(δύο\), twice, and \(\εὐχαρίστων\), superiority), and in Cruciferous flowers there are four long and two short (Fig. 177), the flowers being Tetradyamous (\(τετρά\), Botany.

Stamens in general stand regularly round the pistil, but occasionally their upper portions are curved to one side of the flower, and they become de-clinate, as in the Amaryllis and Horse-chestnut.

The filament is slender and cylindrical, or slightly flattened. It is curved and elastic in the Pellitory (Fig. 254) and in the Nettle, petaloid in the White Water-Lily, and in Indian Shot and Ginger, broadened at the base in Campanula, thickened in Barberry (Fig. 257), with appendages in Borage (Fig. 255) and Asclepias (Fig. 256). The filament is attached to the anther lobes, either by adhering along their whole length on one side, called the back, and the anther is then innate, as in Magnolia, Crowfoot, and Barberry (Fig. 257); or it extends only to the base of the lobes, which are firmly fixed to it, and the anther is innate, as in Carex (Fig. 258), or its apex is attached to a single point of the anther, which then swings easily about, and is called Versatile, as in Grasses (Fig. 165).

The anther presents a groove or depression between its lobes, indicating the place where the septum or partition is situated (Fig. 239, g). Each anther lobe also presents a line or furrow running from top to bottom, and placed more or less laterally. This is called the Suture, or line of dehiscence, and marks the place where the anther opens to discharge the pollen (Fig. 239, f). The suture corresponds to the edge of the leaf; and in innate anthers it is lateral, while in others its position is more or less distinctly on the face of the anther, or on the side opposite to the attachment of the filament. At the suture the epidermal tissue is thin, and the endothecium is wanting.

The face of the anther is usually directed towards the centre of the flower, in which case the anther is called Introrse, as in the Vine (Fig. 238); at other times it is directed towards the circumference of the flower, and the anther is Extrorse, as in the Meadow-saffron and in the Iris. The mode of opening or of dehiscence varies in different anthers. Sometimes the lobes split along the whole face, either in the centre or at the side, longitudinally (Fig. 239), at other times transversely (Fig. 259). Sometimes the slit only takes place at the apex, so as to present two holes or pores, as in Rhododendron and Solanum (Fig. 260), or four pores, as in Parnassia, or two tubes, as in the Heath, or so as to form a separable lid, as in Gamboge. In the Barberry, each lobe of the anther opens by a single valve, which is rolled upwards (Figs. 261, v); and the same thing occurs in many Lauraceae, in which, however, there are frequently four valves, that is, two to each lobe, corresponding to the antherine cavities.

The union of the anther lobes is effected either by a continuation of the filament (Fig. 257), or by a mass of cellular tissue with spiral vessels, called the Connective (Fig. 238). This extends to a greater or less height between the lobes, and is sometimes so narrow as to be inconspicuous, as in Euphorbia. Sometimes it reaches beyond them in the form of a cellular expansion, as in Magnolia, Violet (Fig. 262, p), and Asarum, or of a long feathery appendage, as in Oleander; while at other times it proceeds backwards in the form of a spur, as in the Violet (Fig. 262, e), and in the Heath. It divides into two branches occasionally, each bearing another lobe, as in Sage (Fig. 245), and then it is distactile.

The Pollen—is contained in the anther, and presents the appearance of a minute, usually yellow powder, which, Botany.

when examined by the microscope, is found to consist of cellules (Fig. 263) of different forms, varying from \( \frac{1}{4} \)th to \( \frac{1}{8} \)th of an inch in diameter. Pollen-grains, when fully formed, are usually spherical, oval, or triangular (Figs. 267, 268, 269). In Podostemon the pollen is of an oblong shape, with an hour-glass contraction in the middle; while in Zostera it consists of long slender threads.

Pollen-grains are developed in the large cells seen in the early state of the anther (Figs. 241, 242, cm). Each of these cells is called a parent or mother cell (Fig. 264, cm). Its contents divide first into two, and then into four parts, each of which becomes covered with cellulose, so as to constitute an independent cell or pollen-grain (Fig. 264, p). These grains either burst through the parent cell and become free, or they remain united in fours or some multiple of four, as in many species of Acacia; or in large masses, such as those seen in Orchids (Fig. 265), and in Asclepias, where they constitute Pollinia. The remains of the partially destroyed mother cells sometimes remain in the form of threads.

Each pollen-grain has usually two coverings, the outer called Exine, being a firm membrane marked frequently with bands, reticulations, or rough points (Fig. 266); the inner, denominated Intine, being thin and capable of extension. The intine alone is present in Zostera. In the ripe pollen of the Fir (Fig. 267) the distension of the intine is such as to separate the exine into two hemispherical parts.

In the interior of pollen-grains a minute granular matter exists called Forilla, mixed with starch or oily matter. The forilla granules vary from \( \frac{1}{4} \)th to \( \frac{1}{8} \)th of an inch in diameter. These display motions which are looked upon by some as molecular, or such as are seen under the microscope among minute particles suspended in fluid; while by others they are regarded as analogous to the phytozoic movements seen in the antheridia of Cryptogamic plants.

The surface of pollen-grains is often marked by grooves or folds, or by rounded markings. At these parts the exine is either deficient, or separates like a lid, as in the Passion-flower. When the pollen is moistened in water its grains absorb it and become enlarged, and the intine bursts at one or more points, sending out the forilla (Fig. 268). When the pollen is scattered on the pistil, and is moistened on one side by the fluid of the stigma, the intine, in place of bursting, protrudes in the form of a tube called a pollen-tube (Fig. 269, t). The number of tubes protruded in different kinds of pollen-grains varies.

Transformations of Stamens.—Changes take place in the stamens by suppression and degenerations of various kinds. Whenever the stamens are below the number of the parts of the calyx, we may suspect that there has been some suppression. In many irregular flowers, such as Figwort and Dead-nettle, four stamens only occur, although the parts of the calyx and corolla are five. This depends on the suppression of one stamen, and in the case of Figwort we find a rudimentary stamen in the form of a staminodium attached to the corolla on the upper side. Again, in allied plants, such as Pentstemon, the fifth stamen is produced. The stamens are suppressed in the case of pistilliferous flowers. In flowers with numerous stamens, such as Poppies, Roses, and Crowfoots, there are always some of the stamens abortive, for we do not find two flowers in which the number is the same. It seems to be a law in vegetable organography that the number of the floral organs is less constant the greater it is. Stamens in some plants have a great tendency to be changed into petals, especially in cultivation. When the anther is abortive the filament sometimes produces hairs in its place. In the case of Canna, where only one anther lobe is perfected, the filament becomes petaloid. It is probable that the peculiar gland-like scales of Parnassia are only an altered state of the stamens (Fig. 237). Occasionally the anthers are converted into carpels.

The Disk.—The organ which botanists call the Disk seems to be in many cases an alteration of some of the staminal whorls. This is more especially true of such cases as Gloxinia and Gesnera, where the scales alternate with the developed row of stamens, and where the fifth stamen assumes the form of a scale. The Disk may be said to consist essentially of processes arising from the thalamus between the developed stamens and pistil. In the Orange the disk is in the form of a ring surrounding the base of the pistil; so also in Rue, where it is very large and conspicuous. In the Vine (Fig. 238), the disk-scales are evident. In the Tree Peony (Fig. 270) the disk forms a dark red expansion which covers the follicles. In Umbelliferous plants, the remains of the disk are seen at the upper part of the fruit.

† Gynoecium or Pistilline Organs.

** Pistil before becoming the Fruit.

The pistil is the vertical which terminates the axis of growth, and is placed in the centre of the flower. It is composed of leaves called Carpels or Carpidia (καρπός), from their connection with the fruit. These leaves are folded, so that their lower surface is external, and they are well seen in the Cherry, with double flowers, in which the organs of reproduction are more or less completely altered. In this plant one or more leaves (Fig. 271) occupy the place of the pistil. When there is a single carpel (Fig. the pistil is Simple, and the two terms (carpel and pistil) are synonymous; when there is more than one carpel, the pistil is Compound (Fig. 273, c). The carpels are either distinct or united; and it frequently happens, that by adhesion or obliteration, changes take place by which


**Fig. 271.** Folded carpellary leaf of the double-flowering Cherry. In place of petals, the plant produces leaves.


**Fig. 272.** Pistil of Broom, consisting of ovary, style, stamen, and stigma. It is formed by a single carpel. The terms pistil and carpel are here synonymous.


**Fig. 273.** Vertical section of the flower of Meadow-sweet (Spiraea). The pistil is compound, consisting of several distinct carpels, each with ovary, style, and stigma. The stamens are indefinite, and inserted into the calyx.

the number of the carpels is diminished, so that they do not equal the other whorls. It is rare to find the parts of the pistilline whorl symmetrical with the others. A flower, however, is still called symmetrical if the numbers of the three outer whorls are equal to or multiples of each other.


**Fig. 274.** Compound syncarpous pistil of Primrose (Primula). The five carpels, which it comprises, are completely enclosed in a common pericarp, and the styles, stamens, and stigmas, are united. The flower is called Monogynous, although in reality there are five ovaries.


**Fig. 275.** Pistil of Apple (Pomona Americana), cut vertically. The solitary ovule, ov, is contained in the ovary, which consists of three coats, the innermost of which is the epidermis of the carpellary leaf, and which finally becomes the hard stone of the Apple. The middle, mc, corresponding to the mesophyllium or parenchyma of the leaf, becomes the flesh of the Apple; the outer, ec, becomes the fleshy part of the Apple; and the outer, ep, corresponding to the lower epidermis of the carpellary leaf, and which finally constitutes the skin of the Apple, is prolonged upwards, containing a canal, te, and ending in the stigma, st, consisting of loose cellular tissue uncovered by epidermis.

A pistil is called Apocarpous or Dialycarpous (ἀπό, separate, διάλυσις, to separate, and καρπός, fruit) when all the carpels are separate (Fig. 273); and Syncarpous (σύν, together or united) when they are combined into one (Fig. 274). The parts of a perfect pistil are the Ovary, containing ovules or rudimentary seeds, the Style, and the Stigma. These terms are rather vaguely used, as applying either to the parts of a single carpellary leaf, or to the parts of a pistil formed of more than one carpel, and in which the ovaries, styles, and stigmas are united completely. In Figure 275 the lower portion is the ovary containing the ovule, ov, the style is marked te, and the stigma st. The style is not always present, and, when absent, the stigma is sessile, as in the Poppy.

The ovary of a simple pistil consists of the folded blade of a single leaf (Fig. 276), and resembles it in structure. The outer surface of the ovary (Figs. 275 and 276, ep) represents the lower epidermis of the leaf, sometimes covered with hairs, and, when green, exhibiting stomata; the inner surface (Fig. 275, end, and 276, en) represents the upper epidermis; between these surfaces are placed the parenchyma, and the vascular tissue consisting of woody, spiral, and dotted vessels of various kinds (Fig. 275, me). The midrib is on the outer or dorsal surface, and therefore is inferior, while the two edges of the leaf (Fig. 276, pf) are united at their inner part, or face next the axis, and are superior.

The face of the ovary is called the ventral suture, while the back is called the dorsal suture. At the ventral suture there is a cellular growth called the Placenta (Fig. 276, pd), to which the ovules, ov, are attached often by a distinct cord, cf. As each margin of the folded leaf or carpel forms a placenta, this organ is essentially double, and it sometimes shows its formation by appearing as two lamellae (Fig. 276, pf). Along the placentas the ovules are placed in one or more rows. Sometimes they occupy a small part of the placenta, as in cases where they are reduced to one (Fig. 275) or two. The parenchymatous tissue sometimes becomes hard, as in the nut; at other times it is much developed, and forms a succulent covering, as seen in fleshy fruits (Fig. 275, me).

When the style exists, it is a prolongation of the cells and vessels of the leaf upwards, and represents the narrow portion of an acuminate leaf, folded so as to form a canal (Fig. 275, tc), with loose cells inside. It is terminated by the stigma (Fig. 275, st), which is a loose cellular portion divested of epidermis, and moistened with fluid, so as to retain the pollen-grains when scattered. The stigma is sometimes a mere point, at other times it extends along one or both sides of the style. It is to be considered as continuous with the placenta.

When the pistil is formed of a single carpel, it terminates the axis, and appears to be continuous with it. When the pistil is bicarpellary, that is, formed of two carpels, they are placed opposite to each other, and if they unite, it is by their ventral sutures. The carpels, in such a case, are usually placed so that one is superior, that is, next the axis, and the other inferior, next the bract of the axillary flower, as in the Figwort order. Sometimes, however, they are lateral, that is, to the right and left of the axis in a plane at right angles to the axis and bract, as in the Gentian order, and Cruciferae. When the carpels are more than two, they follow the usual laws of alternation with the other parts of the flower. It is chiefly in apocarpous pistils that the alternation can be satisfactorily seen; for in syncarpous pistils the adhesion which takes place often obscures the arrangement.

The number of carpels in an apocarpous pistil, or the number of separate styles in a syncarpous one (i.e., one in which the ovaries are united), is indicated in the following way:—A flower with a simple pistil or one style is Monoecious (μονοεκος, one, and γυναικειος, female); with two separate carpels or two separate styles, Digynous; with three, Triecious; with four, Tetraecious; with five, Pentacycious; with six, Hexacycious; with seven, Heptacycious; with eight, Octacycious; with nine, Enneacycious; with ten, Decacycious; with twelve, Dodecacycious; with a greater number, Polygonous. These differences are employed by Linnaeus in forming some of his Orders.

In an Apocarpous pistil, the carpels may be arranged in one circle (Fig. 273), or in several (Fig. 277). In the latter case, the inner whorls alternate in succession with the outer. Sometimes they are placed on a flattened receptacle or thalamus, as in Marsh Marigold; at other times on an In a syncarpous pistil, various degrees of adhesion take place. The carpels may unite merely at their inner angles, leaving marked external divisions, as in the Rue; or the ovaries may be completely united while the styles are separate, as in Flax (Fig. 278); or the whole may be consolidated into one, as in the Primrose (Fig. 274). In rare cases the styles and stigmas are united into one body, while the ovaries are separate, as in the Labiate and the Borage orders.

In syncarpous pistils, the number of carpels entering into their composition may be traced by observing the grooves or lobes of the ovary, by the number of styles and stigmas, and, when complete union takes place, by the venation, or by the divisions seen in the interior of the ovary. Thus, in the Lily, the syncarpous pistil is composed of three carpels united, and, by cutting across the ovary (Fig. 279), we observe three loculi containing ovules. The carpels are generally united in such a way, that partitions or dissepiments (septa), more or less complete, are seen on making a transverse section. These are formed by the union of the margins or sides of the carpellary leaves, each septum being essentially double or composed of the laminae of two contiguous carpels. The septa of collateral carpels are therefore vertical, and equal to the number of carpels. There can be no true septum in a single carpel, but spurious divisions (phragmata) may be formed, either in a transverse manner by cellular processes proceeding from the walls of the carpel, as in Cassia Fistula and Desmodium; or in a vertical manner, by projections from the dorsal suture, as in Flax; or by prolongations of the placentas, as in Cruciferae; where a replum is produced; or by a turning inwards of the ventral suture, as in some species of Oxytropis, or of the dorsal suture, as in Astragalus. In the Thorn Apple, the ovary, when cut transversely at the upper part, shows two cavities; but when the section is made at the lower part of the ovary there are four cavities formed by a spurious vertical septum.

When the partitions in the pistil extend to the axis, a transverse section shows a number of contiguous cavities or Loculariements (loculi), with the placentas in the centre bearing ovules (Fig. 280). A compound pistil of this sort composed of two carpels is two-celled (bilocular); of three, three-celled (trilocular), as seen in the Lily (Fig. 279); of four, four-celled (quadrilocular); of five, five-celled (quinquelocular), as in Campanula (Fig. 281); of many, without distinct reference to number, many-celled (multilocular or plurilocular). In these cases the placentas is in the centre, but still connected with the walls of the ovary by means of septa.

When the partitions do not extend to the centre, all the cells or loculi communicate, and hence such a compound pistil is really unicellular, or has one cavity, as in the Poppy and Orchis (Fig. 282). In these unicellular syncarpous pistils there may be seen partitions proceeding to a greater or less extent into the cavity of the ovary, and bearing placentas on their edges. Such placentas are called Parietal, and their number indicates the number of united carpels. These placentas are sometimes nearly sessile on the walls of the ovary (Fig. 283), at other times they are supported on distinct parietal septa (Fig. 284). Such are called cases of parietal placentation, and are considered as showing the formation of marginal placentas, on the edges of carpellary leaves more or less completely folded inwards towards the axis. The ovules, in these instances, are analogous to buds on the margins of leaves, as seen in Bryophyllum (Fig. 141).

Cases occur in which the carpels are united so as to have no apparent folding inwards of their edges, and in which the placentas are placed in the centre, quite separate from the walls of the ovary, as in the Chickweed and Primrose families. This is called Free Central placentation (Figs. 285 and 286). It is by some considered as being produced by the disappearance of the septa, or by their rupture, at an early period of the growth of the ovary, so as to leave the placentas in the This view is strengthened by seeing in some of the Chickweed tribe septa in a very early stage of growth, and imperfect remains of these partitions on the wall of the ovary, even in an advanced stage (Fig. 285). In some instances, however, especially in the Primrose tribe, no vestiges of septa are found, and no marginal ovules at any period of growth (Fig. 286). Hence this kind of free central placentation is supposed to be produced by a prolongation of the axis, and it is therefore denominated Axile—the leaves of the gynoecium being looked upon as united in a valvate manner, and as being verticillate round the placental axis, which bears ovules like leaf-buds. Those who adhere to the view of all placentas being formed on the margins of leaves, have endeavoured to account for cases of free central placentation like those of the Primrose, by considering the placentas as formed by chorisis from the edge of carpellary leaves, or by placentas produced only at the base of the carpel, and, after uniting together in the centre, becoming elongated and enlarged. On the other hand, some advocates of axile placentation not only apply this view to such cases as those of the Primrose, but to all cases of placentation whatever; and, in the case of parietal placentas, think that the axis divides into a number of cellular prolongations, which become attached to the edges of the carpellary leaves.

Marginal placentas are formed either by the edges of a single carpel, or by the edges of two contiguous carpels. The former takes place in apocarpous pistils (Fig. 276, p), and in syncarpous pistils with complete septa (Fig. 287); the latter in syncarpous pistils with parietal placentas (Fig. 282). The placenta does not always bear ovules throughout its whole extent. Sometimes it is ovuliferous (ovule-bearing) only at or near its summit, or in its middle or at its base. In such placentas the ovules are sometimes reduced to one, as in the Common Sea-Pink, and in Composite plants. The placenta in some instances extends from the margin of the carpellary leaves over the whole inner surface of the ovary, as in the Flowering Rush, and in the White Water-Lily. The spreading of the placenta over the surface may give rise to the appearance of ovules proceeding from the dorsal suture, especially when that is the only part of such a placenta which bears ovules.

The carpellary leaves forming the pistil or Gynoecial verticil are usually sessile, but cases occur in which they appear to be stalked so as to raise the ovary. Such an occurrence may be considered as depending either on a prolongation of the axis supporting the pistil, as seen occasionally in certain monstrosities of Rose and of Geum, or on the union of the petioles of carpellary leaves. In the Passion-flower, there is a distinct stalk or gynophore (γυνή, female, and ὁπός, to bear), bearing the pistil. The same thing takes place in some of the Caper tribe; as well as in Lychnis, in the Pink, and in Dictamnus (Fig. 182), where the stalk is short and thick.

When the pistil is free in the centre of the flower it is called superior, and the other verticils are inferior or hypogynous. It is often united to the calyx and the other whorls. When the adhesion between the ovary and calyx or perianth is complete, as in the Gooseberry, the ovary is said to be inferior. In such instances, the petals and stamens, which are attached to the calyx, appear to arise from the summit of the ovary, and are called Epigynous (ἐπί, upon, and γυνή, pistil). Between these two conditions, there are intermediate stages of adhesion, as seen in some Saxifragaceae, where the ovary becomes half-inferior.

In certain cases it has been supposed that the axis forms part of the walls of the ovary by spreading out in a concave manner, in the same way as the expanded axis of Eschscholtzia* seems to form part of the calyx. In the Rose the axis becomes united to the tube of the calyx (Fig. 185), fig. 7, and is prolonged so as to form a hollow cavity or disk, on the inside of which numerous separate carpels are placed.

The Style—is the prolonged apex of the carpellary leaf, and is not an essential part of the pistil. In some cases it seems to be a process from the placenta, as shown by Lindley in Babingtonia. It may, therefore, consist merely of cellular tissue, with spiral vessels, or it may also have woody tubes and other vessels of the midrib and blade of the leaf entering into its composition. A canal traverses it (Fig. 275, t), containing loose cells, called conducting tissue, which is continuous with the placenta. The style (Fig. 274, t) is situated at the proper apex of the leaf (spiculum), but, by changes in the direction of the apex, it frequently happens that the style appears to be lateral, as in the Strawberry, or even basilar, i.e., from the apparent base, as in Lady's-mantle (Fig. 288). In syncarpous pistils the styles are frequently united, so as to appear single (Fig. 274). When the carpels are placed round an enlarged axis, so that their apices are united to the summit of it, the styles, when united, appear to come from the axis of the plant, as in many of the Borage order, and in the Sage. The carpels are called in such cases Gymodioecia (γυνή, pistil, and διοικεῖν, to bear). In the Geranium the styles are united to the prolonged axis or beak, from which they separate when the fruit is ripe (Fig. 183).

The style in its form is generally rounded, but at times it becomes flat, like a petal, as in Indian-shot. In the Bell-flower there are peculiar hairs on the style, apparently connected with the application of pollen. The style in the pistil of Clematis is also hairy, so as to render the fruit ciliate or tailed. A style, apparently simple, may be formed of several united. Frequently the divisions of such a style extend downwards for a certain length, showing the parts of which it is composed, and thus indicating the number of carpels. But there are cases in which the style, proceeding from a single carpel, actually splits into two parts, becoming forked, as in Euphorbia. This splitting is accounted for by the circumstance that the style is in reality double, formed of two sides of the leaf.

The Stigma—is a part of the pistil, composed of loose cells, which secrete a viscid fluid, and which are uncovered by epidermis. This organ is either sessile on the summit of the ovary, as in the Tulip and Poppy, or it is placed at the apex (Fig. 274, s), or on the side of the style. It may be said to be continuous with the placenta, differing from it in not bearing ovules. This connection with the placenta is evidently seen in cases where it can be traced along one or both sides of the style as far as the ovary. Being formed like the placentas, the stigma is essentially double, and sometimes shows a division on one side, as in Drosera and some Euphorbias. The half of one stigma occasionally unites to the half of that next it, thus giving rise to a peculiar abnormality in the relation of the parts.

Stigmas in a syncarpous pistil are either united or free. In the latter case their lobes or lamellae indicate the number of carpels. The united stigmas sometimes become large and orbicular, as in Rock-rose, or capitulate, as in Primrose (Fig. 274, s), or they radiate along a shield-like body, as in the Poppy.* In the Periwinkle the stigma is covered with hairs, and exhibits a marked contraction in the middle like an hour-glass, with a broad rim below. In the Nettle the stigma is covered with hairs radiating from a point, and Botany.

is called penicillate. In the Violet (Fig. 289, s), the stigma has a hooded and hooked appearance.

The name of stigma is sometimes erroneously given to parts of the style. Thus the upper petaloid portions of the style of the Iris (Fig. 290, sty) have been called stigmata, a term which ought to be restricted to the little slits at their apex (Fig. 290, stig). So also the umbrella-like stigma of Sarracenia is in reality an expansion of the styles with the stigmata at their edges. In some stigmata, as those of Mimulus, the two lamellae are irritable, and close when touched. In Orchids the stigma is sessile on the common column (gynostemium, γυνοστήμιον, pistil, and στεγόν, stamen), and appears as a viscid space immediately below the anther lobes.

Transformations of the Pistil.—These are of frequent occurrence, and depend, generally, on abortion of a certain number of carpels, and on adhesions of various kinds. In the apocarpous pistils of Aconite, Nigella, Larkspur, and Parny, we find on the same plant pistils composed of two, three, four, five, and six carpels. In some of the Brambles, Moquin-Tandon has seen all the carpels except one disappear, thus making the fruit resemble that of the Plum. In the case of Leguminous plants, there is usually only a single carpel, although the flower is pentamerous; this state has been traced to abortion of carpels, and the view is confirmed by finding plants in the same natural order with more than one carpel. Pistils of a succulent nature, such as those of the Sloe and Bird-cherry, sometimes assume the form of a pod, like that of the Pea. Occasionally stamens are changed into carpels, and at other times the carpels are transformed into stamens, and bear pollen.

The Ovule—is the rudiment of the future seed (Fig. 275, ov), and in its early state it appears as a minute cellular projection or mammilla of the placenta. It is analogous to a bud produced on the edge of a leaf, or to a bud formed on a branch in cases where the placenta is axile. The cells multiply until the ovule assumes a more or less enlarged ovate form, constituting what has been called the Nucleus, or the central cellular mass of the ovule (Fig. 291, n).

The ovular nucleus alters in the progress of growth, so as to be prepared for the development of the embryo plant in its interior. At the apex of the nucleus an absorption or obliteration of cells takes place, by which a hollow cavity is formed, which becomes lined with a thin cellular membrane (epithelium), and forms the sac in which the rudiments of the embryo first appear (Fig. 292, s). This embryo-sac is surrounded by a cellular layer derived from the nucleus (Fig. 292, n), to which the name of Terceine has been given. In some instances the terceine appears to be the only covering of the sac, as in the Mistletoe. In most cases, however, other cellular layers are formed, which first appear in the shape of annular appendages at the base, and then gradually spread over the central mass. These ovular coverings are usually two, one next the nucleus, and first formed (Fig. 293, s), called the Secundine, and the other on the outside (Fig. 293, p), called the Primine. These two coats or coverings of the ovule are sometimes incorporated so as to appear one.

At the base of the ovule these coverings and the nucleus are intimately united at one point by a cellular and vascular process, called the Chalaza (Fig. 292, ch), where the nourishing vessels enter from the placenta. At the apex of the ovule they leave an opening called the Foramen or Micropyle (πιπόν, small, and πύρην, a gate), through which the influence of the pollen is afterwards conveyed. This foramen extends through both ovular coats, the opening in the outer (Fig. 293, ex) being the Exostome (ἐξω, outside, and ὀστέον, mouth), and that in the inner (Fig. 293, end) being the Endostome (ἔσω, within). The foramen indicates the organic apex of the ovule, while the part connected with the placenta by means of the stalk (Fig. 293, f) called the Funiculus or Podosperm (ποδός, a foot, σπέρμα, a seed), is the base or Hilum.

The relation which the hilum, the micropyle, and the chalaza bear to each other, varies in different ovules. In an Orthotropous (ὀρθός, straight) or straight ovule (straight as regards its axis), the chalaza is at the hilum, and the micropyle at the opposite extremity (Fig. 292). In such an ovule the chalaza, ch, is at the base, and the micropyle, m, at the apex, and no curvature nor inversion takes place either in the nucleus or in its coverings. In a Campylotropous (καμπύλος, curved) or curved ovule, the chalaza is still at the hilum, but the whole ovule is bent upon itself, so that the micropyle or apex approaches the hilum. This is shown in Figure 294, which exhibits a vertical section of the ovule of Wallflower; the nucleus, n, is curved on itself, and so are the primine, p, and secundine, s; the chalaza, ch, is at the base of the ovule, and the foramen or apex is close to it. In an Anatropous (ἀνατρέπω, to subvert) or inverted ovule (Fig. 295), an inversion of the nucleus, n, takes place, so that its base, ch, is removed to the opposite side from the hilum, h, or base of the ovule, and the micropyle, f, is so placed as to be close to the hilum. In this case the chalaza, ch, is at the apertant apex of the ovule, and its connection with the placenta is kept up by a cord, r, called the Raphe, consisting of cellular tissue and of spiral vessels. When the hilum is placed midway between the micropyle and the chalaza, the ovule becomes *Heterotropal* (Greek, diverse), and in such cases it frequently happens that the funiculus proceeds at right angles from the ovule, so that the latter becomes horizontal. Such ovules are considered by some as produced by a partial adhesion of the funiculus to the upper part of one side of the ovule.

Anatropous ovules are very common. They appear to be formed with the view of allowing the pollen tubes to reach the foramen easily. Campylotropous ovules are by no means uncommon. They are met with in Cruciferous and Caryophyllaceous plants, in Mignonette, and in the Bean. The orthotropous form is rare as a permanent condition of the ovule; it is met with in a few natural orders, such as the Buckwheat and Rock-rose tribes. Many look upon it as being the earliest state of all ovules, and refer the other forms to changes produced during growth.

Ovules vary in number. Sometimes there is a solitary ovule in each ovary, or in each loculacium, at other times there are several. When the number is not great, and is uniform, the ovules are said to be *definite*, when very numerous they are *indefinite*. They are attached in various ways to the placenta, and their position in the ovary varies. When the placenta at the base of the ovary is the only part ovuliferous, then the ovule is *erect*, as in Polygonum. When the ovuliferous part is above the base, and the ovules proceed obliquely upwards, they are *ascending*, as in the Peltitory, and if they are developed equally on either side of the attachment, they are *horizontal* or *pettate*, as in Crassula. When the ovuliferous part of the placenta is at the apex of the ovary, the ovules are *pendulous*, as in Valerian, when below the apex, they are *suspended*, as in the Apricot (Fig. 275). In the Common Thrift, a funiculus extends from the placenta to the apex of the ovary, and curves downwards so as to suspend the ovule. When an ovary is multi-ovular (contains many ovules), the ovules may be all attached in the same way, and be placed either collaterally or one above the other (Fig. 279); or they may be attached in different ways, so that some are erect and others pendulous. These terms apply only to the position of the ovule as respects the ovary, and they have reference alike to orthotropous, campylotropous, and anatropous ovules. Thus, an anatropous ovule may be either erect or pendulous as regards its position in the ovary. The same terms apply to the seed in its relation to the seed-vessel.

Some ovules are not contained in a true pistil, i.e., in a carpel consisting of true ovary and stigma. These ovules are met with in the Cycas* and Cone-bearing orders. In the former, the ovules are arranged on the edges of metamorphosed leaves, and the pollen from the male flowers is applied directly to them, without the intervention of a stigma. In the latter the ovules (Fig. 296, oe) are covered by scales, eca, which are hardened bracts or floral leaves covering the female flowers. In this case also the pollen is applied to the micropyle, mic, of the ovules, without the intervention of a stigma.

†† Pistil after becoming the Fruit.

The Fruit—is, properly speaking, the pistil arrived at maturity, containing the ripe seeds, in which the embryo plant is developed (Fig. 297, pt). The simplest form of fruit is that formed by a single carpel, inclosing one or more seeds (Fig. 276). It often happens that changes take place by which some parts of the carpel are rendered succulent, and, then, in place of a dry fruit, there is produced a fleshy one. This is well seen in the case of the Peach, in which the outer epidermal covering of the carpel forms what is called the skin, the parenchymatous cells of the mesophyll constitute the flesh, and the inner epidermis of the carpellary leaf is changed into the stone; the kernel being the ripe seed containing the embryo plant. In the Coco-nut, in place of fleshy cells, woody fibrous ones are produced; the outer layer of the husk representing the external epidermis of the ovarian carpel, the fibrous portion being the parenchyma of the carpel, and the hard shell being the inner epidermis of the carpel inclosing the seed and the embryo.

As in the case of the pistil, so in the fruit, the carpels composing it may be distinct or united. When the fruit consists of a single ripe carpel, or of several separate and distinct carpels, it is said to be *Apocarpous* or *Dialycarpous*, as in the Pea (Fig. 276) where there is a single carpel, and in the Ranunculus (Fig. 277), and Columbine (Fig. 298),

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**Plate CXXXIV.**


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**Fig. 297.** Fruit of a species of Dock (Rumex), cut vertically. It is a monoecious indehiscent dry fruit, called an Achene, or Achene-fruitlet. The pericarp, p, is the pericarpium, or outer coat of the seed, with its contents, which contains nourishing matter, called albumen or pericarpia, a, b, and the embryo plant, p, with its cotyledons, c, d, and the plumule, e. The pericarp is smooth, and the embryo is inserted. At the upper part of the pericarp two of the styles and stigmas are seen curving downward, and the ovary is seen opening at the lower end.

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**Fig. 298.** Apocarpous fruit of Columbine (Aquilegia vulgaris), consisting of five separate mature carpels, with styles and stigmas.

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**Fig. 299.** Fruit of a species of Oak (Quercus), cut vertically. It has three carpels with two ovules in each, of which it is originally composed. Two of the carpels and five of the ovaries are represented in the diagram, and the mature fruit is unicellular and monocarpellate. Surrounding the ovary the mass of brevis is seen.

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**Fig. 300.** Achenes or fruits of the Oak (Quercus), consisting of the ovary containing a single seed, and surrounded by a series of bracts which form the cup or cupula.

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In which there are several separate mature carpels. When the mature carpels are combined, as in the Poppy, the fruit is *Syncarpous*. Sometimes the mature pistils of several flowers are incorporated into one hard or succulent mass, as in the Cone, in the Mulberry, and in the Fig (Fig. 157), and in these instances, what is commonly called the fruit, consists, in reality, of a great number of fruits united together. Such fruits are called *Collective* or *Multiple*.

The fruit may be formed not merely by the pistil, but also by other parts of the flower united to it, more or less completely. Thus, in the Apple, Pear, Gooseberry, Currant, and Melon, the calyx is combined with the pistil; in the Hazel-nut, the Acorn (Fig. 300), and Chestnut, bracts form the husk, the cup, and the hull; in the Rose the receptacle is enlarged, and covers the pistil. Occasionally the fruit seems to consist not merely of a number of rows of transformed leaves, but of a transformed branch in addition.

By ascertaining the anatomy and structure of the pistil, we are led to a knowledge of the nature of the fruit, and we are enabled to see the changes which take place during growth. These changes depend on increase of the parenchyma, adhesion of one part to another, obliteration of lo- culaments or of ovules, and the development of additional processes or partitions from the placenta, and from other parts of the pistil. Thus, the Coco-nut in its young state, is formed by three carpels, each containing a single ovule, while in its mature condition there is only one loculament and one seed. In this case the partitions between the carpels are obliterated, and one ovule is developed at the expense of the other two. These changes may be traced on careful examination; and even in the ripe fruit indications of them are seen in the markings on the shell. The Acorn in its early condition (Fig. 299), is formed of three carpels, with two ovules in each, as seen in the Figure, but in the progress of development changes are induced by which the fruit (Fig. 300) becomes one-celled and one-seeded. In these cases a trilocular sex-ovular pistil becomes a unilocular and monospermic fruit. In the Hazel, the Ash, the Elm, the Beech, and the Horse-chestnut, similar changes are produced in the pistil by the abortion of ovules, and the obliteration of divisions. In the Thorn-apple the pistil is formed of two carpels, separated by a septum, while the fruit exhibits four loculaments, produced by prolongations from the placentas, forming a spurious septum in each carpel.

It sometimes happens that the receptacle or peduncle becomes succulent, and is called the fruit in ordinary language. Thus, in the Strawberry (Fig. 301), the true fruit consists of small single-seeded (monospermic) dry seed-vessels (commonly called seeds), scattered over a succulent convex receptacle; in the Rose, the true fruit consists of similar seed-vessels arranged on a fleshy concave receptacle (Fig. 185); and in the Fig the true fruit consists of mono-spermic seed-vessels produced by separate flowers, and scattered over the inner surface of a concave succulent receptacle (Fig. 157).

In the Cashew,* the nut or true fruit is borne on a coloured succulent stalk, which enlarges during ripening.

In the interior of some fruits a pulpy substance is produced, apparently as a secretion from the inner lining of the ovary. This kind of pulpy matter is met with in the Gooseberry, Currant, Grape, Orange, and pod of Cassia Fistula. Occasionally the organs adjacent to the pistil become the succulent parts of the fruit. In Strawberry-Blite, the calyx surrounding the pistil, and separate from it, becomes red and juicy; in Gaultheria procumbens, the free calyx, after flowering, becomes red and succulent, surrounding the true fruit, which is dry. In the Yew, the bracts enveloping the seed become succulent.

The fruit, generally speaking, consists of the seed-vessel or Pericarp (περικάρπιον, around, and κάρπος, fruit), and the Seed. It cannot be said to be perfect unless the seed and embryo are produced. In many cultivated fruits, however, the seeds are abortive. Thus, in the case of the Bread-fruit, Banana, and Pine-apple, the best fruit is seedless, and such is often true of the Orange and the Grape. The Pericarp, in its simplest state, represents the carpellary leaf, and, like it, can be separated into three parts: the outer epidermal covering (Fig. 302, cp), called Epicarp, or Exocarp, (ἐξωτερικόν, ἐκών, upon, ἐξωτερικόν, outside, ἔξω, fruit), the middle parenchymatous portion, me, called Mesocarp (μέσον, middle), and when succulent, Sarcocarp (σάρκα, flesh), and the inner epidermal covering, en, called Endocarp (ἔσωτερον, within), and when hard and stony Putamen (πυταμέν, the shell of a nut). These three coverings are well seen in the Peach, in the Cherry, and in the Date. In their original structure these parts correspond with the leaf, but changes take place during ripening, by which some cells are hardened and others become succulent, and thus the resemblance to the leaf is much obscured. That succulent fruits, such as the Peach, Apricot, and Cherry, are to be regarded as altered carpellary leaves, is shown in the case of the double Cherry, where true leaves occupy the place of the fruit (Fig. 186). Dr Wyville Thomson records instances of the common Sloe and Bird-cherry producing red-coloured follicular pods. In many fruits, as in the Nut, the different pericarpial layers are so blended that it is not easy to mark their separation.

Some fruits fall without opening or dehiscing, the seeds being liberated during the process of decay; such fruits are Indehiscent (indēhisco, not to open). Other fruits open or dehisc in various ways, so as to scatter the seeds, and are called Dehiscent. The dehiscence takes place either in a vertical or in a transverse direction; the former is the usual mode. Vertical dehiscence takes place through the sutures, or by the separation of the parts of which a syncarpous fruit is composed. The separate parts are called Valves. In fruits formed by a single carpel, the dehiscence occurs either at the ventral or dorsal suture, or both. In the follicles of the Peony, the Columbine (Fig. 298), and the Marsh Marigold, the dehiscence is ventral; in Magnolia grandiflora the dehiscence is sometimes dorsal; while in the pod of the Pea (Fig. 276) and of the Bean, it is both ventral and dorsal.

When the fruit consists of several carpels united, or is syncarpous, the dehiscence takes place either by a separation of the constituent carpels through the dissepiments (Fig. 303), and in that case is Septicidal (septum, partition, and cedo, to cut), as in Figwort and Gentian, where there are two valves, in Meadow-saffron, where there are three valves, and in the Fig-Marigold and the Rhododendron, where there are five or more valves; or the dehiscence takes place by the dorsal suture of each carpel (Fig. 304), and in that case is Loculicidal (loculus, a loculement, and cedo, to cut), as in the Iris, the Pansy, the Lily, and the Horse-chestnut.

There are modifications of these kinds of dehiscence. Thus, in the septicidal form the valves, on separating, sometimes carry the placentas with them, as in Gentian and Colchicum (Fig. 287); at other times, the placentas or placentaries are left attached to the central axis or columnella, as in Rhododendron. In the case of Hura, Euphorbia, and Jasminia,* each carpel, or coccus as it is called, separates from the columella, carrying with it an inclosed seed. In fig. 2, the loculicidal dehiscence the dissepiments may remain attached to the middle of each of the valves, and separate along with them, or the septa may adhere to the axis, and allow the valves to fall off without them (Fig. 305), as in the Thorn-apple and Purple Convolvulus. The latter kind of loculicidal dehiscence is called Septifragal (septum, a partition, and frango, to break). In some cases the dehiscence is at first loculicidal, and afterwards the carpels separate. from each other in a septicidal manner. This union of the two kinds of dehiscence is seen in some Spurges, in the Castor-oil fruit, and in the Purging Flax.*

In Orchis, the placentas, as represented in Figure 282, are parietal, and the seed-vessel opens by three valves (Fig. 306, v), which are placentaferous in their middle, but be founded on a consideration of their original formation, Botany, and of their anatomical structure in the early state. This is often puzzling to the student, inasmuch as it requires that he should trace the fruit during its different stages of development. By so doing, however, he is enabled to observe the various changes which take place by absorption, obliteration, adhesion, and division of parts, and he is in a condition to explain many apparent anomalies. Thus, in the Coco-nut, he sees that there are at first three loculicaments and three ovules, but as the fruit ripens, two of each of them disappear, and finally only one remains. The three ridges, however, which remain on the endocarp, are at once explained by a reference to the early condition of the nut.

Such is the case with many fruits, the structure of which would be obscure without a knowledge of the morphological alterations which have taken place. The names applied to fruits have a reference chiefly to their fully developed condition.

Without attempting to give a rigorous and minute definition of Carpological (καρπός, fruit, and λόγος, discourse) terms which have been multiplied to a burdensome extent, we shall merely explain some of those which are most frequently employed, arranging them according as they refer to fruits formed by a single separate flower, and which are called Simple or Monogynacelial (formed by one Gynoecium); or to fruits formed by a combination of numerous flowers, and which are called Collective, Multiple, Anthocarpos (ἀνθός, flower, and καρπός, fruit), or Polygynacelial (formed by many Gynoecia).

Simple or Monogynacelial Fruits.—These may consist either of a single mature carpel, or of numerous separate carpels, arranged in one or more rows in a circular manner, on flat convex or concave receptacles. They may be formed not only of the pistil but of the other parts of the flower united to it, and they may either be dehiscent or indehiscent, dry or succulent.

A Follicle is a fruit formed by a single mature carpel dehiscing by the ventral suture (Fig. 312). The fruit may consist of a single follicle, as is seen occasionally in the Peony; more commonly it is formed by two or more separate follicles arranged in a circular or spiral manner, as in the Marsh Marigold, and Columbine (Fig. 298). In some follicular fruits the opening takes place by the dorsal suture.

A Legume. This is commonly known by the name of pod, and is well seen in the case of the Pea (Fig. 276). It consists of a single mature carpel dehiscing both by the ventral and by the dorsal suture, so as to separate into two halves. This kind of fruit is characteristic of the Pea order,* which has hence been called Leguminosae. Some legumes, as those of Cathartocarpus Fistula, do not open; others have divisions between each of the seeds formed by transverse foldings, as in Sainfoin (Fig. 313), and Bird's-foot. The latter is called a lomentaceous or moniliform legume or a Lomentum, and when mature it usually separates into pieces, each of which contains a single seed. In some legumes, a spurious division is formed in a vertical manner by a prolongation from the placenta, or by a folding inwards of the dorsal suture. The legume is sometimes twisted, and spiral; at other times it has a leafy and inflated aspect, as in Bladder-Senna. In some legumes, the outer portion or the exocarp (epicarp) separates from the endocarp, which still remains covering the seeds. In some indehiscent monospermal legumes the coverings become succulent; so that they are really drupaceous, thus establishing a connection between the Leguminous and Rosaceous orders.

A Silique is another kind of pod, formed (according to most authors) by the union of two carpellary leaves with

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*Plate CXXVIII. Pimpnel, Purslane, and in various species of Monkey-pot (Fig. 311), in which the upper part of the fruit separates like a lid. This is called Circumscissile (circum, around, and scissilis, cleft) dehiscence, and seems to indicate that the seed-vessel in these cases is formed by jointed leaves which separate at the articulations—the united petioles forming the lower part of the fruit, and the united lamina constituting the lid.

Carpology.—A classification of fruits ought properly to Botany, parietal placentas, and delhisce by two valves which separate from below upwards. It is well seen in the common Wallflower (Fig. 307), and in other Cruciferous plants. The two valves separate from the placentas, leaving them united is closely applied to the seed. At first sight it is difficult to distinguish this kind of seed-vessel from a seed, and hence Linnaeus termed some achene-bearing plants naked-seeded (gymnospermia—γυμνός, naked, ὁρίζων, a seed). It is common to find several separate achenes forming the fruit. In Buttercups, the achenes are aggregated on a convex receptacle (Fig. 277), in the Strawberry they are placed on a convex succulent receptacle (Fig. 301), and in the Rose on a concave receptacle (Fig. 185). In all these cases, the presence of styles and stigmas enables the student to ascertain that what are commonly called seeds are in reality fruits. In the instances already noticed, the numerous achenes are the produce of a single flower, but cases occur, such as the Fig (Fig. 157) and Dorstenia (Fig. 156), in which they are each the produce of a separate flower. In the Borage and Mint orders, the two or four achenes forming the ripe fruit (Fig. 318) are at first united, and even when matured, there is a common style which is attached to the apparent base of each achene. Cases also occur in which the achenes are united to the tube of the calyx.


**Fig. 314.** Lomentum or lomentaceous legume of a species of Sainfoin (Hedysarum). Each seed is contained in a separate cavity by the folding inwards of the walls of the legume at equal intervals; and the interior is filled with ripe seeds.


**Fig. 315.** Compound ovary (Silique) of Wallflower (Cheiranthus), consisting of at least two carpels united. One valve has been removed to show the two carpels, c, c, united by their free margins to form a common placenta, ca, on either side, to which the ovules, o, are attached by means of funiculi. The style and stigma, s, are at the upper part of the ovary.


**Fig. 316.** Silicula of White-thistle (Dipsacus), opening by two flat valves, o, from the back and sides, leaving the seeds, s, exposed on the outside, united by a membrane or replum. The partition of the seed-vessel is broad, and hence the name Lateralis.


**Fig. 317.** Achene of Crowfoot (Ranunculus). A one-seeded, dry, indehiscent fruit, with the pericarp applied closely to the seed. The fruit resembles seeds in appearance; the style and stigma aid in distinguishing them.


**Fig. 318.** Calyx and fruit of Camfrey (Spergularia) cut vertically. The fruit is divided into four sections, each containing a single-seeded portion or achene, two of which are seen in this figure, while the style appears to arise from the base of the carpel.


**Fig. 319.** Fennel (Foeniculum vulgare), one of the Umbelliferae, cut vertically showing the fruit, f, consisting of four single-seeded portions, p, or achenes, united, as to form a syncarp. The pendulous heads consist of many small flowers. The two styles are seen at the apex of the fruit, with their dilated bases formed by a ring round each. The points (apicula) of the petals, p, are turned inwards. The calyx is adherent to the fruit, and the limb of the calyx is often obsolete.

Thus in Composite plants, such as the Thistle and Dandelion, what are called seeds are in reality single-seeded fruits, each produced by a separate flower, with the tube of the calyx united to it, and the limb of the calyx appearing as a rim or as a hairy appendage, called pappus (Figs. 206 and 252).

In Umbel-bearing plants, such as Hemlock and Fennel, two achenia, invested by the tube of the calyx, are united by their faces, so as to form a compound fruit called a Cremocarp (κρεμάω, to suspend, and καρπός, fruit), with a division or commissure between them (Fig. 319). This fruit, when ripe, shows its composition by separating into two achenes (called here, mericarps or hemicarps, μέρος, part, ἅμισυς, half), which are suspended by a slender central stalk or axis (Fig. 320), called a Carpophoré (καρπός, fruit, and φορέω, to bear). The outer surface of these mericarps is marked by ridges and furrows, and there are often peculiar vittae or receptacles of oil present in the pericarp.

A Caryopsis (καρπός, a nut, and ἀπόση, appearance) is a dry in- Botany.

Dehiscent monospermous seed-vessel resembling an achene, but differing in the complete adhesion and incorporation which exists between the pericarpial covering and the seed. It is seen in the common cultivated grains, as Wheat and Oats (Fig. 321), and in general in all Grasses. In these plants the pericarp cannot be separated from the seed. Hence the grains of Wheat, Maize, Barley, Rye, and Oats, are in common language called seeds. It is only by examining them in the early state, and noticing the styles, that we can determine their real nature.

A Nut is a dry unilocular one-seeded indehiscent fruit with a hard covering. In its early state, it is usually composed of two or more carpels, with one or more ovules in each; but, in the progress of growth, all disappear except one. It is illustrated by the Hazel-nut, the Chestnut, the Acorn (Fig. 300), and the Coco-nut. In many cases it is surrounded by a series of bracts forming an involucre, seen in the husk of the Nut, the cup of the Acorn, and the burr of the Chestnut. Some restrict the term nut (glans) entirely to such cases. The pericarp of the nut has its parts frequently so united as not to be distinguished from each other. In the Coco-nut, however, the pericarp can be separated into an epicarp or outer covering, a fibrous mesocarp, and a stony endocarp, marked with three ridges and three depressions, one of which is perforated. The epicarp of the nut of the Sago-Palm is scaly.

A Samara (Samara, seed of Elm), is a nut or acheneum, in which the pericarp is extended in the form of a winged margin or apex. There are originally two carpels united, but one of them is frequently abortive. This samaroid fruit occurs in the Maple (Fig. 322), and Sycamore, the Ash, and the Elm. The samara of the Sycamore opens by splitting into two in a septal manner.

A Drupe is the general name given to what are called stone-fruits, such as the Peach, the Plum, the Cherry, the Apricot, the Date, the Olive, and Coffee. It is a one-celled, one or two-seeded indehiscent fruit, having a fleshy mesocarp, which is hence denominated sarcocarp. In the Peach, the epicarp is the separable skin, the sarcocarp is the flesh which is eaten, and the endocarp is the hard shell or putamen, which can be split into two parts. In the Walnut, the putamen is divided in a marked manner into two, and from its interior bony partitions extend, so as to form lobes in the seed or kernel. Some fruits, such as the Almond, are called drupes or drupaceous, in which the sarcocarp is not succulent. Many call the Coco-nut a drupe, with a fibrous mesocarp. There seems to be, in reality, in such cases, a transition from the drupe to the nut. The aggregation of several drupes forms the fruit of the Raspberry, the Bramble, and the Quassia plant.

A Berry or Baccia, is the name given to all indehiscent syncarpous fruits, the seeds of which are immersed in a pulpy or fleshy mass. Such fruits are collectively called baccate or berried. In the true berry, such as the Gooseberry and Currant, the calyx adheres to the fruit, and the placentas are parietal (Fig. 323), while in the grape (Uva) the ovary alone is present, and the placentas are central. Instances of baccate fruits are seen in Solanaceous plants, such as the Potato, Belladonna, Winter Cherry, (Fig. 207) and Mistletoe.

In the Pomegranate there is a peculiar succulent berried fruit, called a Balanista (balanistium, the flower of the Pomegranate), in which the pulp cells are arranged in two rows, some of which are in the centre round the axis, and others are placed outside, all being adherent to the calyx. In the Orange there is a modification of the berry, called Hesperidium (the golden fruit in the garden of the Hesperides) in which there is a separable rind not formed by the calyx, consisting of epicarp and mesocarp, and pulpy separable cells formed by the endocarp.

A Pepo is a fruit allied to the berry, occurring in the Cucumber and Melon (Fig. 324). It consists of three carpels united, covered by a firm rind, which is partly formed by the calyx. The placentas are by some considered as parietal, and as sending processes inwards, by others they are looked upon as central, and as sending processes outwards, which reach the walls of the fruit and then curve backwards, bearing the seeds. The processes proceeding from the axis to the walls are usually obliterated, according to the latter view, giving rise to the appearance of the placentas being parietal. The fruit thus becomes one-celled. A transverse section of the Melon is given in Fig. 324, in which pf indicates the placentas, cf the septa, and s the processes connecting the curved placentas with the centre. In the Plantain and Banana, the fruit is allied to the pepo, consisting of three carpels, with parietal placentas, the perianth being adherent to the ovary, and the seeds immersed in a pulpy mass when ripe.

A Pome is a fleshy syncarpous fruit composed of two or more scaly, or horny, or bony carpels, covered by a pulpy mass, which is incorporated with the calyx. The outer fleshy portion may be considered either as the combined epicarp and mesocarp, or it may be reckoned the receptacle enlarged, as in the Rose, and united to the calyx. This kind of fruit is seen in the Apple (Fig. 325), the Pear, the Quince, and the Medlar. The cartilaginous cells inclosing the seeds of the Apple, and the bony coverings (nucleus) of the seeds of the Medlar, may be reckoned either as the endocarp, or as the entire pericarp, according to the view taken of the formation of the pulpy exterior.

Multiple, Collective or Polygynacal Fruits.—These fruits are formed by the Gynoecia of several flowers united, and the name anthocarpous is also applied, because they consist usually of the bracts and floral envelopes combined with the ovaries. They are either indehiscent or dehiscent, succulent or dry. A Cone, Strobilus (στροβίλος), a fir-cone, is a form of collective fruit, composed of scales or bracts covering one or more naked seeds (Fig. 296). Some consider these scales as carpels spread out, but from the absence of style and stigma, they seem more properly referable to floral leaves or bracts. The cone gives name to the natural order Coniferae, or Cone-bearers, such as the Fir and Larch. In the Juniper the scales of the cone are succulent, and the fruit has sometimes received the name of Gallulae. In the Yew the bracts enveloping the naked seed also become succulent.

In the Fig (Fig. 157) a multiple fruit occurs, called Syconus (συκών, a fig), consisting of numerous flowers inclosed in a hollow receptacle. What are called the seeds of the Fig, are in reality monospermous seed-vessels (achenes), with styles and stigmas. In the Mulberry, Bread-fruit (Fig. 326), and Pine-apple, the ovaries and floral envelopes of several flowers are all united into one fleshy mass, placed on a more or less convex or elongated receptacle, and the fruit is called a Sorosis (σωρός, a congeries or cluster). The crown of the Pine-apple may be regarded as a series of empty bracts terminating the axis. In the strobili of the Hop, the bracts covering the flowers are membranous in place of being succulent.

Transformations in Fruits.—The same causes which produce alterations in the other parts of the flower, give rise to anomalous appearances in the fruit. The carpels, in place of bearing seeds, are sometimes changed into leaves, with lobes at their margin. Leaves are sometimes produced from the upper part of the fruit, which is then called frondiparous (from, a leaf, and paro, to produce). In the genus Citrus, to which the Orange and Lemon belong, it is very common to meet with a separation of the carpels, so as to produce what are called horned oranges and fingered citrons. In this case a syncarpous fruit has a tendency to become apocarpous. In the Orange we occasionally find a supernumerary row of carpels produced, giving rise to the appearance of small and imperfect oranges inclosed within the original one. It sometimes happens that, by the union of flowers, double fruits are produced. Occasionally, a double fruit is produced, not by the incorporation of two flowers, but by the abnormal development of a second carpel in the flower.

The Seed.—When the ovule arrives at maturity it constitutes the seed, which is contained in a seed-vessel in the plants which are called Angiospermae (ἄγγιος, a vessel, and σπέρμα, a seed); while, in Gymnospermae (γυμνός, naked, and σπέρμα, a seed), such as Coniferae and Cycadaceae, it is naked, or, in other words, has no true pericarpial covering. By far the larger number of flowering plants belong to the former division. It sometimes happens in Angiosperms, that the seed-vessel is ruptured at an early period of growth, so that the seeds become more or less fully exposed during their development; this occurs in Mignonette, where the capsule opens at the apex, and in Cuphea, where the placenta bursts through the ovary and floral envelopes, and appears as an erect process bearing the young seeds.

The seed (Fig. 327) consists of a nucleus, c, usually covered by two cellular integuments, e, and te, which are sometimes included under the general name of Spermoderm (σπερμόδερμα, a seed, and δέρμα, skin). The outer integument is denominated the Episperm, Exosperma, or more commonly the Testa (Fig. 327, te). It corresponds usually to the primine of the ovule, but it is frequently formed by a union of both primine and secundine. It varies in its texture, being sometimes thin and membranaceous, at other times thick and hard. It presents various colours, being brown, white, red, black, and mottled. Its surface sometimes presents ridges and furrows, as in Larkspur, reticulations, as in the Water Cress, alveolar depressions, as in the Poppy, and tubercular eminences, as in Chickweed. Occasionally, the seminal integument is furnished with appendages in the form of wings, as in Pine seeds (Fig. 328) and Bignonia, or with a margin as in Sandwort; and at other times it is provided with hairs, as in the Cotton plant, Asclepias (Fig. 329), and the Willow. It is of importance to distinguish between such hairs and the pappus of Composite plants, and of Valerian,* which is in reality an abortive calycine limb attached to the fruit. We CXXII. have already stated that the presence of the style or stigma fig. 3, distinguishes single-seeded fruits from seeds.

The seed of some Polymoniacous plants has a covering, consisting of small cells or hairs containing spiral fibres inside. These hairs are closely applied to the surface of the episperm, and are confined by a mucilaginous coating. When placed in water, the mucilage dissolves, and the hairs are liberated, so as to spread out in all directions. The walls of the cells are also usually ruptured, so as to allow the spiral fibres to uncoil, and form a beautiful object under the microscope. The same kind of structure occurs in the pericarpial covering of some Labiate plants, such as Salvia, and of some Composite plants, such as Senecio. The spreading out of these fibrous cells is apparently intended for the purpose of fixing the seed in the moist soil, into which they are carried by the wind. Sometimes the secundine of the ovule assumes a succulent consistence in the seed, and forms a lining to the episperm.

The Endopleura or Tegmen is the inner seminal envelope or integument. In general, it is formed from the tercine or the membrane of the nucleus, and it is sometimes united with the embryo-sac. In some cases, as in the Water-Lily, Ginger, and Pepper, this sac remains as a distinct covering of the young plant under the name of the vitellus (Fig. 333, es). The endopleura is often incorporated with the testa, and scarcely separable from it. It is composed usually of a thin layer of cellular tissue, and when the nucleus is sinuous, as in the Walnut, it follows its windings, so as to enter between the lobes.

The spermoderm, or general seminal integument, has certain markings corresponding to those mentioned in the ovule. Thus, we observe the micropyle or small opening in the coats which extends to the nucleus (Fig. 327, m), the chalaza (Fig. 327, eh) or the fibro-vascular connection between the nucleus and the coats, and the base or hilum by which the seed is connected with the funicle (Fig. 327, f). These parts bear the same relation to each other as they do in the ovule. Thus, in an orthotropous seed, the hilum and chalaza are united, and the micropyle is at the opposite end or apex; in a campylotropous seed, the hilum and chalaza are united, and the micropyle is slightly removed from the hilum; while in an anatropous seed, the nucleus is inverted—its base and the chalaza being removed from the hilum, and the micropyle being close to the hilum.

The micropyle is smaller and less distinct in the full-grown seed than it was in the ovule. It indicates the place where the radicular extremity of the embryo is situated. Its situation in the Bean and Pea, when they begin to sprout, is marked by a little lid-like process (embryotega) which is pushed upwards. The chalaza is more or less evident in different seeds. It is conspicuous in anatropous seeds, such as the Orange (Fig. 330, c), where the raphe (Fig. 331, r) or vascular connection between it and the placenta exists. The raphe forms a cord usually along the inner side of the seed, and may be considered as a prolongation from the funicle, along with a covering derived from the integument of the seed. The scar or hilum is of different sizes and colours, and indicates the base of the seed or the place where it is attached to the placenta. This attachment is either direct, or is accomplished by the intervention of a stalk or cord called the funicle, which in Magnolias becomes much elongated. In the Bean the scar is of a black colour; in other cases it is white or brown. It sometimes extends over a large portion of the seed, as in the Horse-chestnut.

On the outside of the integument of the seed there is sometimes an additional partial covering of a cellular nature which is developed after the ovule is fertilized, and which has received the name of Aril (arillus). It proceeds from the placenta or top of the funicle in some instances, while in others it arises from the funicle or the seed. In the former case it is called a true or funicular aril, while in the latter it is called a false or micropylar aril, or sometimes Arilode. In the Passion-flower and Water-Lily, a funicular aril exists, while in the Spindle-tree, Nutmeg, Spurge, and Milkwort, a micropylar aril (Fig. 332, a) is seen. In the Nutmeg, the arilode is laciniated and of a fine scarlet colour, constituting the mace. Certain cellular processes are occasionally seen at the base, apex, or sides of the seed, which fig. 6 have received the names of Carnules and Strophiolites.

The different parts of a seed are represented in Figure 333, a being the nucleus or central portion, composed of nourishing matter including the embryo-sac, es, with the embryo-plant, e, the radicle of which points to the micro-ple, m; f the funicle, ch the chalaza, r the vessels running from the placenta to the base of the nucleus, i the integuments or spermoderm, and a a the funicular aril.

The nucleus or kernel of the seed (Fig. 333, n) is the fully-developed central portion of the ovule. It is much altered in general by the deposition of starchy, azotized, and ligneous matter, and by the development of the embryo. It consists either of the embryo alone, as in Wallflower (Fig. 334), or of the embryo along with a separate deposit of nourishing matter called the Albumen or Perisperm, as in the Pansy (Fig. 335). This albumen consists of starchy, ligneous, oily, saline, and nitrogenous substances contained in cells of various consistence. It is, therefore, not merely what chemists call vegetable albumen; and hence it is better to give it the name of perisperm or endosperm.

A seed is said to be albuminous or perispermic when it has a separate store of albumen distinct from the embryo, as in the Coco-nut, Wheat, and Pansy (Fig. 335); and exalbuminous or aperispermic when the nutritious matter is incorporated with the lobes of the embryo, as in Cruciferous plants (Fig. 334), in the Bean, the Pea (Fig. 327), and Almond. The perisperm varies in its consistence according to the nature of the deposit and the state of the cells. In the Vegetable-Ivory Palm, the cells are thickened by ligneous deposits, and the perisperm is of a horny consistence; so also in Coffee. In the Cereal grains, as Wheat, it is mealy and farinaceous; in the Poppy it is oily; in the Coco-nut it is cartilaginous; in the Mallow, mucilaginous. When cut, the perisperm may present a uniform appearance, as in Castor-Oil, or it may have a mottled or riminated appearance, as in the Nutmeg and Betel-nut. The latter depends on some unaltered cells of the endopleura or of the CXXXL embryo-sac ramifying through the substance and forming convolutions. The proportion which the perisperm bears to the embryo varies much. Sometimes, as in the Coco-nut, in the Date, and in Monkshood, the embryo is very small, while the albumen is abundant; at other times, as in the Nettle, the embryo is large and the albumen small. The deposit of albumen takes place within the integuments of the seed. It either occupies the space between the endopleura and the embryo-sac, when it is called exospermic, as in the Water-Lily and other plants which have a distinct vitellus; or it is deposited within the sac, and then is endospermic; or it occupies both positions at once, and then may be called by the general name of perisperm.

The Embryo—is the young plant contained in the seed. It is the part to the production and nourishment of which all the floral organs contribute. It is contained originally in a cavity called the embryo-sac (Fig. 333, es), and appears at first as a small vesicle or cell (Fig. 333, e), attached to the sac by a cellular process called a suspensor, which is often very long, as in Cruciferous plants. The embryo-sac is sometimes separated from the endopleura by a quantity of perisperm (Fig. 333, n), at other times it is incorporated with it. The embryo-sac exhibits peculiar tubular prolon- The Embryo in its structure exhibits cells and spiral vessels. It consists of a general axis, one part of which is concerned in the production of the root (Fig. 335, p), and another in the formation of the stem (Fig. 335, co). The radical or root-portion of the axis always points to the micropyle of the seed. Hence, in orthotropous seeds, the embryo is said to be inverted, because its radicle points to the apex of the seed where the micropyle is situated, while in anatropous seeds (Fig. 335) it is erect. The axial portion of the embryo is provided with foliaceous or fleshy organs called seed-leaves (Fig. 335, eo) or Cotyledons (sorobolos, name of a plant with fleshy leaves), which serve a temporary purpose in nutrition. From the upper part of the axis, the stem called the Plumule rises, bearing the ordinary, or primordial leaves of the plant. These separate parts are well seen when the young plant has begun to grow, as in Figure 59, where t is the general axis, with the roots, r, at the base, the cotyledons, c e, above, and the plumule with the primordial leaves, g g, coming from between the cotyledons.

The embryo is sometimes placed in the centre of the albumen, or in the axis of the seed, and in a straight direction (Fig. 335), it is then axile or axial; when not in the centre of the seed it is abaxile or eccentric. In place of being straight it is often curved in various ways. This may depend on the curvature of the seed itself, as in the Snake-nut, and in Campylotropous seeds; or the seed may be straight, and the embryo alone curved. In the Chickweed order the embryo is curved round the albumen (Fig. 336), becoming peripherical. In other cases, as the Thorn-apple and Solanum, it is curved in a similar way within the albumen. In Grasses it is situated at the base of the seed, and outside the albumen (Fig. 321). In the Poppy the embryo is in the axis, but is curved or arcuate, in Geranium the cotyledons are twisted and doubled, in Convolvulus they are corrugated, and in the Potato and in Buphias they are spiral. In some Cruciferous plants the cotyledons are bent like a leaf folded laterally on its midrib, and they are then called conduplicate, and marked o >; in other Cruciferous plants, they are flat, and the radicle is either bent along their edges, as in Wallflower (Fig. 337, r), and marked o =; or lies on the back of one of them, as in Rocket (Fig. 338, r), and marked o ||. In the former case, the cotyledons c are accumbent, in the latter incumbent. Some authors speak of the position of the embryo not merely in reference to the seed, but also in reference to the fruit. This is apt to lead to confusion. A superior or ascending radicle is the name given by them when it points to the apex of the fruit, while an inferior or descending radicle points to the base of the fruit; a centripetal radicle points to the centre or axis of the fruit, while a centrifugal one points in the opposite way.

In some plants, the embryo is entirely cellular and has no cotyledons. They are denominated Acotyledonous. They correspond to Cryptogamic or flowerless plants. The embryo, in such cases, is called a Spore (Fig. 8). It gives off roots and stems from different parts of its surface, and not from any fixed points. It may either be regarded as an ovule remaining in a cellular state, or as a simple cellular embryo. It will be noticed when treating of the organs of Cryptogamic plants.

Plants which possess cotyledons in their embryo (Figs. 57 and 61) are called Cotyledonous, and they are divided into those having two cotyledons (Fig. 59), and which are called Dicotyledonous, and those having one (Figs. 60 and 63), called Monocotyledonous. The former correspond with the Exogenous division of Phanerogamous or flowering plants, the latter with the Endogenous. A dicotyledonous embryo at first appears in the form of a cell, (Fig. 333, e), the production of which in the embryo-sac depends on the application of the pollen to the stigma. This cell is nucleated, and develops others in succession, until the embryo assumes the appearance of a congeries of cells suspended by a cellular filament (suspensor) as shown in Figure 339, 1. The globular cellular mass becomes afterwards more elongated, and passes through the stages 2 and 3 of Figure 339 until it assumes the appearance seen at 4, having an oblong or cylindrical form, with one extremity, a, undivided, and the other, b, lobed or notched. The undivided portion is the radicle (young root), and it may be considered as part of the rudimentary axis, from one end of which the roots are given off; and from the other the primary bud or plumule. The split portion of the embryo is composed of two lobes or cotyledons, formed at one node, and placed opposite to each other.

The cotyledons vary in their consistence, being sometimes leafy, at other times fleshy. They are sometimes so large as to form the great bulk of the seed, as in the Bean, Pea, and Almond. They form the first bud of the axis, which may thus be said to consist of a radicular and cotyledonary portion—their point of union being the Collum, neck, or crown. The part interposed between the neck and the cotyledons, which is often very short, is sometimes called the Cauliculus or Tigellus. The dicotyledonous embryo then is composed of two leaves or two unifilar phytoms, as they are called, united together so as to form one axis. The sheathing lower part of the cotyledons helps to form the caulicule; and from the axil of the cotyledons, or from the axis between them, is produced the plumular or gemmular bud (Fig. 339, g g), which forms the stem and leaves. This embryo may be represented by the ideal Figure 340, in which b is the axis or tigellus, a the radicular portion, connected with the soil and darkness, d the two cotyledons, united at their lower part so as to form the tigellus, and e the primary bud or plumule, connected with air and light. The embryo may be called a bifilar phyton.

Although this is the usual state of the embryo in Exogens, nevertheless there are a few exceptions. In some Exogens without leaves, as the Dodder* and Rafflesia, the cotyledons are also suppressed. The embryo of these plants has a resemblance to the spore of Acrogens. In Cone-bearing plants, as the Pine, Spruce, Fir, and Cedar, the cotyledons are split by collateral chorisis, so as to be divided into several (Fig. 341), and this has given rise to the term polycotyledonous applied to them. The cotyledons of the Geranium and Lime-tree are divided into lobes. Accidental divisions are also seen in the cotyledons of the Sycamore and Rue. In Schizopetalon and some other Crucifers, the cotyledons are usually bipartite, so as to appear to be four. A monocotyledonous differs from a dicotyledonous embryo in having only one cotyledon or seed-leaf (Fig. 63, e). It is composed of an axis having a radicular portion, r, and a cotyledonary portion, c, and it may be represented by a single leaf or a unifloral phyton. In Figure 342 is given an ideal representation of a monocotyledonous embryo, with its tegillus or axis, b, having a radicular portion, a, one coty-

Fig. 341.

Fig. 342.

Fig. 343.

Fig. 344.

Fig. 345.

Fig. 346.

Fig. 347.

Fig. 348.

Fig. 349.

Fig. 350.

Fig. 351.

Fig. 352.

Fig. 353.

Fig. 354.

Fig. 355.

Fig. 356.

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Fig. 358.

Fig. 359.

Fig. 360.

Fig. 361.

Fig. 362.

Fig. 363.

Fig. 364.

Fig. 365.

Fig. 366.

ledon, d c, with a sheathing base, and a bud in its axil, e, which rises as the stem. When this embryo is examined in the seed, it frequently exhibits no marked divisions—the cotyledon being coiled round the axis like a sheath, and embracing the plumule so as to conceal it. This is the case with the embryo of the Coco-nut. Sometimes a monocotyledonous embryo has more than one cotyledon. In that case, the second cotyledon alternates with the first, being produced at a second node, which is separated from the first by an internode.

Transformations in Seeds.—Changes take place in seeds by abortion, degeneration, and union. There are few plants in which all the ovules become perfect seeds. Many are suppressed during the progress of growth, so that frequently one seed is developed at the expense of several ovules. Sometimes the seeds are converted into leaves. There is usually a single embryo in each seed, but cases occur in which a plurality of embryos is produced. This is a very common occurrence in the Orange, Cycas, and Cone-bearing orders. In the case of the two latter orders, the suspensor often ramifies so as to produce numerous separate embryos on its branches. These embryos are frequently abortive. In the seed of the Fir there are certain cellular bodies, called corpuscles by Brown, which give origin to filaments by which the embryos are suspended. Accidental union of embryos also take place.

II.—REPRODUCTIVE ORGANS OF FLOWERLESS PLANTS.

It has already been stated that Flowerless or Cryptogamic plants are composed either entirely of cells, as occurs in Seaweeds and Mushrooms; or of cells and vessels united, as seen in Ferns, Mosses, and their allies. The vascular tissue consists chiefly of pleuroenchyma (Fig. 24) with closed spirals, annular (Fig. 32), and scalariform vessels (Fig. 34). In the simplest plants, as Protococcus (Fig. 343), the cell performs all the functions necessary for the nourishment and reproduction of the plant. In the more complicated Flowerless plants, there are some organs specially adapted for nutrition or vegetation, and others for reproduction. In the higher Cryptogams, there are roots, conspicuous stems, and leaves for the purposes of nutrition, and certain special organs destined for reproduction. As these tribes produce a foliaceous axis or corm, they are denominated Cormogens or Cormophytes, and when their stems are woody, they present the acrogenous structure already described. In the lower Cryptogams there are no true roots, nor stems, nor leaves, and their nutritive and reproductive organs are frequently assimilated. These tribes, from having no foliaceous axis, but simply a cellular expansion, have been called Thallogens or Thallophytes.

While the nutritive organs of Cryptogamic plants bear a greater or less resemblance to those of Phanerogams, the case is very different with the reproductive organs. Cryptogams have no flowers and no true seeds; they are propagated by cellular bodies denominated Spores (Fig. 344), which are cells capable of sprouting and forming new plants, (Fig. 358), and which some have called cellular embryos without cotyledons, or leafless phytos. The plants are consequently Acotyledonous.

The term spore (σπόρος, seed) should be confined to the ultimate germinating cell of Cryptogams. It is frequently, however, applied to the cell in which the true spores are formed. Hence spores have been called simple or compound, according as they are formed by one or by several cells. The term Sporidium is applied to the compound spore of Lichens (Fig. 345).

Spores are developed either in the interior of the cell which gives origin to them, or on the outside of it. In the former case, they are called Endospores, in the latter, Exospores or Gymnosporae. In Protococcus (Fig. 343), the fructification consists of numerous spores in the interior of a mother-sac, more or less spherical; in Palmella (Fig. 11), the mother-cell contains two or four spores; while in Vaucleria, only one spore is produced. A cell containing one, four, six, eight, or numerous spores or sporidia, receives the name of Theca (Fig. 346, f).

The exospores or naked spores in certain Moulds consist of elongated filaments which are formed by a series of cells placed end to end (Fig. 18, e). When ripe, the cells separate. In Botrytis a single spore only constitutes the exospore, while in Cantharellus there are two, and in Agarics four (Fig. 347, sp). Leveillé called the mother-cell, on the exterior of which one, two, four, or many spores are formed, a Basidium (Fig. 347, b). In Agarics, the basidia bearing four spores at their extremity are ingeniously united together so as to form a tissue called Hymenium (Fig. 347, h). In Lichens, Sphaerias, and Pezizas, the thecae containing four, six, or eight spores or sporidia placed one above the other are often separated by filaments or Paraphyses (Fig. 346, p); and the united thecae and paraphyses constitute the hymenium, which is placed on the tissue forming the cortical or medullary layers called the subhymenium (Fig. 347, sh). The spore-bearing tissue is sometimes called generically the Receptacle; it may be flat, as in Usnea, and is then called Apothecium, or hollow, as in Peziza, and then called Receptacle; or it may form a closed cavity with an opening (ostiolum) only at one part, and then it is called a Conceptacle. In Ferns and Mosses, Botany.

the hollow cavities containing the spores receive the name of Sporangia (σπόρος, seed, ἀγγελος, a vessel) or spore-cases.

Spores are generally regarded as being produced by the agency of certain organs equivalent to the stamens and pistils of Phanerogams. These organs have been demonstrated more or less completely in all the orders of Cryptogamic plants, and they have received the names of Anthéridia (Fig. 348, a), and Pistillidia or Archegonia (Fig.


Fig. 348. Anthéridium, a, of the Hair-moss (Polytrichum), consisting of cells, each containing a spermatozoon in its nucleus. The protoplasts have a thickened extremity, where proceeds a tapering tail-like process. Along with the anthéridium are two separate filaments, each consisting of several cells, and terminating in a small globular mass.


Fig. 350. Spores, a, of a Fern (Pteris longifolia) sprouting, giving off a root-like structure, b, and a flat cellular expansion, c, called the pro-thallus or pro-embryo. On this expansion anthéridia and pistillidia are said to occur.

349—ἀρξιν, beginning, and γένος, offspring), the former representing the stamens or the male, the latter the pistil or the female. The anthéridia were early noticed by Hedwig in the case of Mosses, and their presence has of late years been detected in nearly all the Cryptogamic tribes. In Mosses and in Liverworts anthéridia and archegonia occur on the fully-developed plants. In Ferns and Horse-tails, they are seen on a cellular structure of a leafy character, called the Pro-embryo or Pro-thallus (Fig. 350), developed from the spores.

In anthéridia there have been detected cells containing moving filaments, Phytozoa, or Spermatozooids, or Anthéridozoids (Glos, an animal—Fig. 348, c). Each phytozoon (Glos, a plant, and Glos, an animal) is formed in a special cell, is rolled upon itself in a spiral manner, and escapes either by a pore or by a dissolution of the wall of the cell. It is often furnished with slender threads at one extremity (Fig. 351). In the thecae and sporangia, also, of many Cryptogamics, certain moving spores have been observed, furnished with vibratile threads or cilia (Fig. 8). These spores have been denominated Zoospores or Spermatozooids (σπόρος, a seed, τοξος, an animal, τοξος, resemblance). Their motions seem to be connected with vibratile processes which vary in number, and which proceed from different parts of the spore.

Filicose Ferns.—These Cryptogamic plants are composed of cellular and vascular tissue. They have roots, leaves, an acrogenous stem, containing scalariform vessels, and an acotyledonous embryo. The stem or Candex either rises conspicuously into the air, as in the case of Tree-ferns with their elegant foliage, or it appears as a rhizome running along the surface of the earth or under ground, as seen in the native Ferns of Britain. The trunk of Tree-ferns is hollow when fully formed, generally simple, sometimes dichotomous, having on the outside leaf-scars which display the markings of the vascular bundles (Fig. 88). The leaves, which are called Fronds, are produced at the summit of the stem, and they form a very graceful crown or coma. In the young state, they are rolled up in a circinate manner, so as to resemble a crozier (Fig. 100). They consist of veins and parenchyma, the former being usually of equal thickness throughout, and divided in a forked (fucate) or reticulated manner. The epidermis has stomata, but they are not very numerous. The fronds bear the fructification. In some instances they produce bulbils or gemmae, which, when separated from the plant, take root and give rise to new individuals; such Ferns are called Bulbiferous or Gemmiparous.

The fructification in its fully developed state appears as Sporangia, or Spore-cases, situated on the veins on the back, or on the margins of the leaves, containing spores. These spore-cases are arranged in clusters (sorti) of a round (Fig. 352, s) or elongated form, and they are either naked or covered by a layer of the epidermis, which forms an Indusium or Indusium (Fig. 353). This indusium presents various forms, and is pushed off during growth in different ways, according to its mode of attachment to the leaf. It sometimes happens that the sporangia, in place of being in clusters on the back of the frond, as in the dorrisferous fructification, appear in the form of a simple or branched spike, as in Osmunda.

The sporangia commence as cellular buds from the parenchyma. Some of the cells constitute the stalk when present (Fig. 354, p), others form the sporangium, s, in the interior of which spores are formed. It frequently happens that the cells outside the sporangium form an Annulus or ring (Fig. 354, a), which is either vertical, and attached by its base, as in Polyody, or horizontal and free, as in Hymenophyllum. The cells composing the ring have walls which vary in thickness on the inner and outer side, and by their unequal contraction finally rupture the delicate sporangium, so as to allow the spores to escape. The ring is very obscure and imperfect in some Ferns, as Osmunda, and it is wanting in Moonwort and Adder's-tongue, and in many other Ferns. Hence, some Ferns are called annulate (having a ring), others exannulate (not having a ring). The spores are covered by a double membrane, and the outer layer is marked with points (Fig. 344). These spores, during germination, give rise to the pro-thallus or pro-embryo (Fig. 350), bearing the anthéridia and archegonia.

Equisetaceae, or Horse-tails.—The plants of this Cryptogamic order exhibit cells, vessels, a siliceous, striated epidermis, and stomata. They have roots, rhizomes, or underground stems, and aerial branches, but no true leaves. The rhizomes sometimes extend to the depth of many feet. The stalks sent up from the rhizomes are hollow and jointed, the articulations being separable, and surrounded by toothed sheaths (Fig. 355, s).

The fructification in its advanced state consists of spore-cases inclosing spores, attached to the under surface of shield-like hexagonal scales (Fig. 356), and collected into a common pyramidal head (Fig. 355, f). The scales (Fig. 356, s) bear on their under surface a circular row of membranous sacs elongated like teeth, t. The sacs open towards the centre of the scale, or that part to which the stalk is attached. Within these sacs there are mother-cells which produce each a single spore. This spore is provided with two elastic spiral appendages, which at first completely cover the wall of the mother-cell and inclose the spore, but finally spread out so as to burst the walls of the sac (Fig. 9, a, b). The spore, when sprouting, produces a pro-embryo or pro-thallus, which at first appears as a green-lobed leaf supported on a stalk. The lobes of the pro-embryo extend and subdivide until a number of cellular septate tubes are produced, containing green matter. It is in this state that bodies resembling the antheridia of Ferns have been detected, as well as peculiar cells, which have been regarded as equivalent to archegonia.

*Lycopodiaceae,* or *Club-mosses.*—These plants have creeping stems or corms, which produce leafy branches, having some resemblance in general appearance to Mosses. Structurally they consist of cells and vessels, the latter occurring in the form of woody and annular vessels, which occupy the axis or central part of the stems. Roots are given off from the primary stem, as well as from different parts of the branches. The leaves are small and sessile, imbricated (Fig. 357, l), or verticillate, and on their epidermis stomata exist in small quantity. The fully-developed fructification occurs in the axil of leaves, which are often collected together in the form of a spike, f. The fructification is of two kinds, one being kidney-shaped, two valved cases (Fig. 358), containing minute cells, which are discharged in the form of yellow dust, known as Lycopode powder, and used, from its inflammable nature, in place of sulphur. The other kind of fructification consists of a roundish and somewhat four-sided body, called by Müller *Oophoridium* (from *o* eggs and *phoros*, to bear), containing four large spores in its interior, and opening by two valves (Fig. 359). These large spores, called *ovules* by some, germinate and reproduce the plant. While the first mentioned organ is considered by some as an antheridium containing grains like those of pollen, the latter is looked upon as the plasmidium with ovules.

*Marsileaceae,* Rhizocorpea, or Pepperworts.—These plants have creeping stems with leaves, which are divided into three or more cuneate portions, and have a circinate vernation. The leaves have stomata and veins. The stem increases by its extremity. It contains a central vascular bundle consisting of woody and scalariform vessels surrounded by parenchyma. The fructification is produced at the base of the leaf-stalks. It consists of *Sporocarps* (*spora*, a seed, and *sporos*, fruit), or ovoid sacs inclosing organs of reproduction. In Figure 360 is represented the two-valved sporocarp or involucre, s, of Marsilea open, and giving out a cellular cord (called by some the midrib of the modified leaf forming the involucre), which at first was curved in a ring-like manner so as to unite the valves, and which finally is detached at one end, p, bearing the reproductive spike-like masses, f, on its surface. These masses consist of antheridia and pistillidia inclosed in first in sacs, and attached to mucilaginous placentas. The pistillidia give origin to the sporangia or ovules, each containing a single germinating spore.

*Musci* or *Mosses.*—These plants have stems bearing minute cellular leaves. The stems consist of cells which in the periphery are polyhedral, while in the centre they are elongated. There is no plexenychma nor true vascular system. In many Mosses the stem terminates at a certain epoch, by bearing the organs of reproduction. Such stems are determinate, and the Mosses are called *Aerocarpous* (*spora*, top, and *sporos*, fruit). In other cases the principal stem ends in a leaf-bud, and continues to elongate, the organs of reproduction appearing on lateral branches. Such stems are indeterminate, and the Mosses are called *Pleurocarpous* (*spora*, side, and *sporos*, fruit).

The leaves, when produced on the stem, are called *caulinary*; when they surround the reproductive organs they are called *perichaetial* (*spora*, around, and *yalyn*, stalk). The latter are usually more approximated than the others, and form a sort of rosette, in the centre of which the reproductive organs are situated. The leaves are very thin in their texture, and are frequently composed of a single cellular layer. The cells usually contain chlorophyll, but sometimes, as in Sphagnum, they are colourless. The cells are either uniform in their size and appearance or a certain number towards the centre are elongated, so as to form veins or ribs. The phyllotaxis of Mosses is usually $\frac{1}{2}$, $\frac{3}{4}$, or $\frac{5}{8}$. Buds, or what are called Innovations, are often produced in the axil of the leaves. These buds, when detached, become new plants.

Occasionally the reproductive organs of Mosses have a peculiar leafy covering or Perigone, formed by the adhesion of three or six small leaflets, which are quite distinct from the perichaetial leaves. The organs of reproduction are of two kinds: one, consisting of cylindrical, pear-shaped, or ellipsoidal stalked sacs, containing minute cells, with phytozoa or spermatozooids in their interior (Fig. 348); the other being also stalked sacs, of a more or less spherical form, containing germinating spores. The former constitute the antheridia, the latter the pistillidia or archegonia. These organs sometimes exist together on the same plant; at other times they are on separate plants. In the former case the Mosses are monoecious, in the latter dioecious. When both these organs are not only on the same plant, but also surrounded by the same perigone, the term hermaphrodite has been applied by some.

The antheridia of Mosses are produced from little clusters of leaves, which differ from those of the stem. They appear in the form of cellular, cylindrical, clavate bodies (Fig. 348, a), containing at first a mucilaginous fluid, and finally very minute, quadrilateral cells, c, (sometimes called Zoosporangia—$\zeta\sigma\omega\sigma\alpha$, animal, $\theta\beta\sigma\pi\alpha$, a sac), in each of which a spiral phytozoon is seen. The antheridia deliquesce by irregular openings at their apex, so as to discharge their contents. Along with the antheridia there are cellular jointed filaments (Fig. 348, p), called Paraphyses, which are considered to be an abortive state of these organs. The archegonia, often mixed with paraphyses or abortive filaments, arise also from small clusters or rosettes of leaves (Fig. 361, f), and appear in the form of spherical or obovate bodies having an outer envelope (epigone) and a central cellular nucleus. In the progress of growth, the central portion increases and rises upwards, and, at the same time, the epigone is ruptured near the base—one portion of it remaining below in the form of a small sheath (ragi-ruda), the other being carried up on the fruit-bearing stalk in the form of a Calyptra (Fig. 361, c). This calyptra is sometimes split at one side (Fig. 361), so as to become dimidiate (halved), and at other times it is either entire or split equally all round the base, and it is then called mitriform. The nucleus or central portion, when fully developed, constitutes the Sporangium. The sporangium is usually supported on a stalk or seta (Fig. 361, p), formed by the lower cells of the nucleus. The seta is often twisted, and, from its hygroscopic property, it produces changes in the position of the sporangium, according to the state of dryness or moisture of the atmosphere. A species of Funaria or Cord-moss, receives the name of hygrometrica, on this account.

The sporangium in its young state is a mass of cellular tissue, the cells of which are homogeneous, and contain green matter. When mature, it is an urn-like body (Fig. 20), with a cellular central axis called columella, and a cavity containing spores. In some instances the sporangium is indehiscent; in other cases it opens either by four lateral valves, as in the Split-moss (Andrea), or by means of a lid called an Operculum (Fig. 20). Sometimes there is a thickening or swelling called apophysis, at the union of the seta and urn.

When the operculum is removed, the opening (stoma or mouth) of the sporangium is seen. This is sometimes entire, as in Mosses called naked-mouthed (gymnostomous, $\gamma\mu\nu\nu\sigma\tau\omega$, naked, and $\sigma\tau\omega\alpha$, mouth); at other times it is surrounded by a Peristome ($\tau\epsilon\pi\tau\omega$, around, and $\sigma\tau\omega\alpha$, mouth), formed by prolongations and divisions of the two inner parietal layers of the sporangium (Fig. 20, p). The peristome consists of one or more rows of hygroscopic cellular teeth, which are either four, or some multiple of that number. When there is one row of teeth, the Mosses are called Apoperistomati ($\alpha\pi\omega\pi\tau\omega\tau\omega\tau\omega\tau\omega$, single); when there are two rows, the Mosses are called Dipoperistomati ($\beta\epsilon\pi\tau\omega\tau\omega\tau\omega\tau\omega$, double). The peristomatic processes (teeth) are sometimes twisted as in Tortula. In some Mosses the inner parietal layer appears as a membrane called Epiphyseum or Typanum, stretched across the mouth, from the walls of the sporangium to the columella.

Hepaticae or Liver-worts.—In these plants the vegetative system (organs of nutrition) consists either of a simple cellular expansion or thallus, or of an axis bearing cellular leaves. In Marchantia this thallus (Fig. 362) bears the organs of reproduction, as well as cup-like bodies with toothed edges, containing little germs or bulbi, g, which are not traced to a reproductive process, and differ from buds, in being contained in peculiar organisms.

In Hepaticae, the reproductive organs consist of zoosporangia or antheridia, and archegonia or pistillidia, either on the same or on different plants. The antheridia are small cellular sacs of a globular, ovoid, or flask-like form, (Fig. 363). They have a single or double cellular coverings, enclosing viscid matter, in which are developed four-sided cells, in each of which is a small filiform body, rolled up in a circular manner, and displaying rapid movements. These bodies, called phytozoa, are finally liberated, and unroll themselves, appearing as filaments swollen at one extremity, and gradually tapering to the other.

The archegonia or pistillidia of Hepaticae are either situated in the substance of the thallus, as in Riccia, or they are raised upon stalks, as in Marchantia and Jungermannia. In Marchantia there stalks bear radiated receptacles on the under surface of which the sporangia are placed. These sporangia have a membranous covering called epigone or calyptra, the upper end of which elongates like the neck of a bottle (Fig. 349 a), so that the pistillidium resembles a pistil, with its ovary, style, and stigma. When the sporangium is raised on its stalk, the calyptra is ruptured irregularly; its lower portion remaining in the form of a sheath round the base of the stalk. The pistillidium, thus formed by the central cellular spore-bearing sac and the epigone, is surrounded also by a cellular sac called the perigone (Fig. 349, b), which begins in the form of a ring at the base, and ultimately forms a cup-like covering. Occasionally there are certain cellular filaments, or perichetial leaves, surrounding the perigone (Fig. 349, c). In Marchantia the perigone incloses a single pistillidium; in Jungermannia it incloses several, but only one is developed. Along with the spores in Hepaticae there are elastic spiral fibres called elaters.

Lichenes or Lichens—are cellular plants growing on stones, on the surface of the earth, and on trees, and taking up nourishment by all points of their surface. They belong to the Thalloid division of Cryptogamia, in which no vascular tissue is seen. Their vegetative system varies much in its form and appearance. Sometimes it appears as fine pulverulent matter in the form of a leprous or mealy crust; sometimes it is a foliaceous expansion, as in Parmelia (Fig. 364), and in Iceland Moss; sometimes it is in the form of filaments, as in Archil, of horn-like processes, or of branching stalks, as in the Reindeer Moss; and sometimes it is a gelatinous mass.

The vegetative system is sometimes called the thallus. It consists of two layers of tissue, one called cortical, in which the cells are more or less rounded, the other medullary, in which there are both round and filiform cells. The spherical cells of the medullary layer (Fig. 365, g), are generally filled with green matter, and, in certain circumstances, they become detached and form separate individuals. These green cells have received the name of Gonidia.

The reproductive organs of Lichens consist of thecae (sporangia of some), often accompanied with paraphyses. While these represent the archegonia or pistillidia, there is no good evidence of the existence of true antheridia. Itzigsohn has recently indicated the presence of antheridia containing spermatozooids, but his observations have not been confirmed by Tulasne and others. The thecae contain four, eight, twelve, or sixteen sporidia (Fig. 346), which are cells with spores in their interior. The sporidium in its early state consists of two nucleated cells (Fig. 345), which in the progress of growth become changed, so that ultimately the mature sporidium contains numerous minute spores. The thecae and paraphyses are usually united together, so as to form a mass of fructification of a circular, cup-like, globular, or linear form. The fructification, when circular, is called Apothecium and Patella (Fig. 364), when linear, Lirella. Sometimes the fructification is covered by a cortical layer of cells (peritheciun) varying in colour, black, red, or pale, which ultimately gives way, either by a pore or by irregular dehiscence. This is seen in what are called Angiocarpous Lichens.

Fungi.—These are cellular plants having neither leaves, nor stems, nor roots. The organs of nutrition or vegetation consist of whitish anastomosing filaments called Mycelium (μύκης, a fungus) or spawn (Fig. 18, m), which spread like a network through the substances on which the Fungi grow. From this network proceed bodies resembling globes, circular disks, mitres, cups, and coralline branches, which bear the organs of reproduction. The mycelium is developed either under ground, or in the interior of the substance on which the plant grows. The filaments of the mycelium are composed of elongated colourless cells.

The organs of reproduction are produced at different points of the mycelium, sometimes solitary, sometimes several together. They at first appear as small tubercles composed of very minute hexagonal cells. These tubercles increase and present different phenomena according to the nature of the plant to which they belong. Thus in Egerita, the tubercle, after attaining its full development, is covered with filaments, each bearing a spore at its extremity; in Peziza, it is hollowed out into the form of a cup more or less deep, the interior of which is lined with thecae or asci; in Agaricus, it produces a pileus or cap-like body borne on a long stalk which comes from the interior of the tubercle, CXXXVI, and bears the fructification externally; in Lycoperdon it forms in its tissue numerous lacunae, from the circumference of each of which are produced elongated cells bearing four spores on their surface. Some Fungi vegetate under the surface of the ground, and either produce their fructification there, as the Truffle (Fig. 366), or above ground, as the

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**Fig. 364.** A Lichen (Parmelia), with its cellular expansion (thallus), and its rounded apothecia, or spots of fructification.

**Fig. 365.** Vertical section of an apothecium and the pileus of a Lichen. Rounded from the upper side, coloured, and filled podial, are seen in the centre of the thallus. These podia, which are called pilei, are buds by some, and capsules by others, which repose on the plant. They constitute the active part of the Lichen, and are surrounded on each side by integumentary layers. Sometimes they burst through the integumentary wall. The apothecia, or spots of thecae and paraphyses, its upper surface is often coloured and covered by a peritheciun.

**Fig. 366.** The Truffle (Tuber cibarium), a subterranean Fungus, with a black tubercle and a waxy external covering, and a white cellular interior containing sporeiferous cells.

**Fig. 367.** Vertical section of a Mushroom (Agaricus campestris); m, mycelium; n, pileus; o, ring, being the remains of the velum, veil, or cortical lamellae or gills of the hymenium; p, the pileus.

Mushroom (Fig. 367). A very large number, however, are developed as parasites in the interior of living or dead organized bodies.

The organs of reproduction of Fungi* are spores, either naked or contained in these or ascii, which are mixed with certain filaments called antheridia. Little is known in regard to the latter. When spores are produced in the interior of distinct sacs, called Thecae or Cystidia (Fig. 368, cys—kivors, a bladder), they are denomi-

nated Endospores, and the plants are said to be thecosporous; when they are developed on the exterior of sacs called Basidia (Fig. 368, bas—Bares, foot), they are denominated Exospores, and the plants are basidiosporous; when produced in the midst of a gelatinous mass, without any evident organization, they are called Myxospores (muca, mucus), the plants being myxosporous.

The fructification is composed either of a single transparent colourless cell, of a rounded or spindle-like form, at the end of each filament (Fig. 369 a); or it is composed of several cells united in a linear series (Fig. 18) or irregularly. The cystidia and basidia are either monosporous or tetrasporous (Fig. 368, spo). When either of these kinds of fructification are united into a mass along with paraphyses, they form what is called the Hymenium (Fig. 368, h—tispa, a membrane). The hymenium is either naked, as in the Hymenomycetous Fungi, or it is inclosed in a membrane called Peridium, as in Gasteromycetous Fungi. This membranous covering may be either single or double.

In the Mushroom (Fig. 367) and other species of Agaricus*, the following are the usual organs observed:—A mycelium or spawn, my, developed under ground, bearing tubercles which consist of the reproductive organs inclosed in a volva or wrapper. This volva, rof, is ruptured in the progress of development. The Agaric is then seen to be composed of a pileus, p, supported on a stalk, st, called a stipe. On the lower side of the pileus is the lamellar hymenium or gills, la, bearing spores. The hymenium was first covered by the volv or indusium, which finally gives way, leaving only a ring, an, round the stalk.

Algae.—Under this name are included numerous plants which grow in the sea, in rivers, lakes, marshes, and hot springs. Their structure is such that they can only grow in water; when exposed to the air they wither and cease to grow. They have no true leaves and no proper stem, but consist of a thallus or cellular expansion which varies in colour—being brown, red, green, or yellow. In some of the larger Seaweeds, as D'Urvillea utilis and Lessonia fuscescens, the thallus is supported on a thick stalk, which exhibits in its structure the appearance of concentric circles. These stalks, however, are composed entirely of cellular tissue arranged in a peculiar manner. There is no vascular system and no woody fibre in their composition. Some species have root-like processes by which they are attached to rocks. These are only intended for fixing them to a spot so as to allow the fronds to be properly exposed to the water, and they do not appear to act as special nutritive organs.

The structure of Algae is cellular, and the cells vary much in form. Some of the cells are round or elliptical, others square, others elongated. The absorption of nourishment takes place throughout the whole substance of the thallus. On the surface of some Alge, as the Charas, carbonate of lime is deposited, and sometimes, as in Corallines, the whole texture is so permeated by this substance, as to become of a hard and stony consistence.

In Alge the reproductive organs vary in their appearance. They consist of spore-cases, which are often aggregated together in Conceptacles (Fig. 369 b), along with Antheridia containing spermatozoids (Fig. 370, a). The spores are often united in fours in a mother-cell, forming a tetraspore (Fig. 371, t). There are also present in many

Alge Zoospores or Sporozooids, which exhibit movements during a certain period of their existence, and are provided with filamentous vibratile processes.

In some of the lower plants of this order, such as Diatomaceae (Fig. 13), an evident division of cells takes place; and in this way the plants are propagated. In Protococcus, the plant of Red and Green Snow (Figs. 56 and 343), and in Palmella, the plant of Gory Dew (Fig. 11), and their allies, the whole plant separates into cells, which may be considered either as buds or spores. In these plants no special reproductive organs have been detected. In some of the Conferve, as well as in Diatomaceae, the union of cells takes place in a singular manner, so as to give rise to the formation of germinating spores (Fig. 19).

Diatomaceae or Brittleworts—are among the simplest forms of Alge. They are usually composed of united rectangular fragments of a brittle nature, which separate at certain periods of growth, and form new individuals (Fig. 13). The true Diatoms have a siliceous covering, so that they retain their form when dry, and are not destroyed by fire; while the division called Desmidiae have no siliceous covering, and alter much on drying. In some of the plants of the order, the union of cells, called Conjugation, has been observed, similar to what takes place in Conferve.

Conferve and their Allies.—These are plants usually of a green colour, consisting of round or cylindrical cells united (Fig. 17), so as to form a filamentous or a flattened thallus. In their simplest form they are seen in the Palmella (Fig. 11), consisting of a single globose cell, dividing first into two, and afterwards into four cells, which finally burst the mother-cell, and escape. Each of these divisions, like the parent cell, has the power of vegetating, and of dividing, by a merismatic process, into four, so as to multiply the plant. In Vaucheria, the terminal cell is concerned in the production of a germinating cell or spore, which has peculiar motions. In Achlya proliferis the terminal cell discharges numerous moving spores. In Zygnema and other Conferve (Fig. 19), the cells composing the filaments have the power of giving out lateral cellular processes, by means of which a union takes place, the result being the production of a spore, either in the tube between the filaments, or in one of the cells of the filaments. The cells in these plants appear to have different functions, and to correspond to the antheridia and pistillidia of the higher Cryptogams.

Florideae; or Rose-coloured Seaweeds.—These Algae are usually of a rose or purplish colour, and consist of variously-formed cells, arranged either in a single row, or in several rows, so as to form an articulated or an expanded flat and often divided thallus. The organs of reproduction are restricted to particular parts of the thallus, and consist of spore-cases, containing spores, frequently four in number, intermixed often with antheridia, or filaments containing spermatozoids, these organs being placed in the interior of conceptacles. The reproductive organs exist either in cavities of the thallus, or in distinct sacs produced on the surface of the thallus, or at the apex of some of its divisions. The occurrence of Tetraspores (Fig. 371), or mother-cells containing four spores, is general in this division of the Algal alliance. The antheridia consist of septate filaments, the terminal cell of which assumes a clavate form, and contains phytozoa. The latter become free by the dissolution of the walls of the cell. Besides the tetraspores, sacs (cocciidia or ceramidia) of a rounded form exist, containing minute spore-like bodies (Fig. 372), which some call sporules. They appear to germinate, and differ from buds, in being contained in special sacs; some consider these cellular bodies as bulbils, which separate from the parent plant; others look upon them as another kind of spore.

Fucaceae, or Brown Seaweeds.—These are usually brown or olive-coloured plants, growing chiefly in salt water. They consist of cells, which are united so as to form various kinds of thalli. Sometimes the thallus is supported on a distinct stalk, formed of elongated cells; and in the frond there occur also thickened cellular lines, having the appearance of veins. The cells of the thallus are often agglutinated together by a gelatinous intercellular substance. The reproductive organs consist of spore-cases and antheridia, contained in conceptacles (Fig. 369 b), which are aggregated together in receptacles, or large club-shaped expansions, at the extremity or margin of the thallus and its divisions (Fig. 397). The antheridia are sacs (Fig. 370 a) borne on jointed filaments, and containing moving phytozoa. Antheridia and spore-cases are seen on the same or on different plants.

Characeae or Charas.—These plants are considered as allied to Algae, although they present many marked peculiarities. They consist of an axis formed by elongated tubular cells (Fig. 21), either transparent, or incrusted with carbonate of lime. From the axis arise branch-like processes, arranged in a verticillate manner. In the interior of the tubes of these plants, distinct circulating motions are seen under the microscope. The reproductive organs of Charas are of two kinds, one called the Globe (Fig. 373 g), a spherical body, containing filaments with phytozoa, the other denominated the Nucleus (Fig. 373 n), an oval body containing a germinating cell or spore. The nucleus is produced on the axil of a branch, and consists of a large central cell or spore, surrounded by five cells, which are wound round it in a spiral manner, and ending in five tooth-like processes at the apex. The globe is usually placed immediately below the nucleus, and consists of eight valves, including a cavity in which the filamentous articulated phytozoary cells are contained. The cells in the interior of the valvular cavity are filled, like those on the flat portion of the valves, with red granules.

On the apex of cells projecting from the centre of each valve, there are numerous filaments (Fig. 374), composed of cells containing minute phytozoa, coiled up in a spiral manner. These escape from the cell, and exhibit spontaneous movements (Fig. 351).

II.—PHYSIOLOGY OF THE REPRODUCTIVE ORGANS.

I.—PHYSIOLOGY OF THE FLORAL ENVELOPES.

The appendages of the flowers which assume a green colour perform the same functions as leaves, giving out oxygen under the influence of light. The cells of the floral leaves or bracts, and of the calycine leaves or sepals, commonly contain chlorophyll, which is produced under the agency of light by a process of deoxidation, carbon being fixed and oxygen separated. The bright-coloured parts of flowers do not appear to decompose carbonic acid; on the contrary, they exhale this gas. The corolla is associated with the thalamus or receptacle in producing abundance of starch, which is changed into sugar during flowering, so as to afford nutriment to the stamens and pistils. While the calyx and green parts of the flower are concerned in the elaboration of the juices under the influence of light, the corolla is more immediately concerned in the protection of the internal organs, in the formation of coloured juices, and in the production of amylaceous and saccharine matter. The quantity of starch accumulated in the receptacles of flowers is often large. This is well seen in Composite, such as the Artichoke and Thistle. The amylaceous matter during flowering in these plants becomes saccharine, and is absorbed by the flowers for their nourishment.

The flower, according to Saussure, in the exercise of its functions, absorbs oxygen gas, and gives out carbonic acid. The absorption of oxygen is carried on by the coloured corolla, along with the essential organs of reproduction. The organs of plants which consume most oxygen are those which wither most quickly, viz. the stamens, styles, and petals. The quantity of oxygen absorbed is much greater when the stamens and pistil are perfect than when they are abortive or wanting. A perfect flower, with the latter organs present took up more oxygen than one which had become double by the more or less complete conversion of the stamens and pistil into petals.

Common Stock, Single Red, consumed 11 times less of oxygen. Common Teabose, Single, 7-7 Indian Cress, Double, 7-4

In proportion to their volume the essential reproductive organs absorb more oxygen than the entire flowers; and male flowers consume more oxygen than female ones.

At the same time that oxygen is absorbed there is a conversion of starch into grape sugar, an evolution of carbonic acid gas, and in many instances a very marked elevation of temperature, caused by the combination between the carbon of the flower and the oxygen of the air. The starch, which is stored up in the receptacle and at the base of the petals, by passing into the state of dextrin and grape sugar, becomes fitted for vegetable nutrition. At the same time important purposes are served in the economy of the plant. Thus the saccharine and honey-like matter which often collects in the cup of the flower, and sometimes in special pits or depressions, as in Crown Imperial (Fig. 55), attracts bees. Botany, and various insects, which are thus made instrumental in scattering the pollen. According to Vaucher, the saccharine matter is applied to the stigma and other parts of the pistil, so as to favour the application and bursting of the grains of pollen.

An evolution of heat takes place during flowering; but from the large surface exposed, it seems to be in most instances carried off by the atmosphere as soon as it is developed. Cases occur, however, in which the temperature can be noted. Thus the flower of a Cistus showed a temperature of 79°, while that of the air was 76°, and those of a Geranium 87° when the air was 81°. Otto ascertained that the flowers of Victoria regia at Hamburg gave out heat when the anthers were mature. Mulder found the flower of Cercis grandiflora 1° to 2° F. warmer than the atmosphere. M. Teysman at Bantenzorg, in Java, observed an elevated temperature in the male cone of Cycas circinalis.* By means of an air thermometer Saussure found the flowers of Polyanthes tuberosa 1½°, those of Bignonia radicans 1°, those of Cucurbita Pepo 1° to 3° F. above the temperature of the air.

The most marked instances of the evolution of heat, however, occur in the blossoms of plants belonging to the natural order Araceae. In them the inflorescence consists of a thick fleshy spadix (Fig. 166) containing much starch, and bearing numerous male and female organs inclosed in a large sheathing bract or spathe. Senebier found that the temperature of Arum maculatum* rose to 15-5° F. above that of the air, and Dutrochet measured it from 25° to 27°.

Goeppert states that the temperature of the spadix of Arum Dracunculus rose to 31-5° F. above that of the air surrounding it. Brongniart in 1834 found the temperature of Colocasia odora 19-8° F. above the air of the conservatory in which the specimen grew. From Dutrochet's examination of the spadix of Arum maculatum it appears that the maximum of temperature in the spadix occurred at 5:30 p.m., one hour and a half after the complete opening of the spathe, and that the heat was 18-7° above that of the surrounding air.

The seat of the highest temperature changes during flowering. When the spathe opens, the staminal organs show the greatest heat; and after the pollen is discharged, their temperature falls, and the part of the spadix above them grows warm. Hubert states that the outer surface of the spadix is that in which the temperature is principally developed. The male organs of the Arum have a higher temperature than the female. There is also exhibited during flowering a daily maximum and minimum of temperature, which, however, do not appear to occur at regular periods. In the case of Arum maculatum, Dutrochet found the maximum temperature at 5:30 p.m., while Senebier noticed it after six in the evening. In Colocasia odora, Brongniart found the maximum at 5 p.m.; Vrolk and De Vriesse, as well as Van Beek and Bergsma, at 3 p.m.; Hasskarl, in Java, at 6 a.m.; Hubert, in Madagascar, after sunrise. In the gardens of Paris, Amsterdam, and Leyden, Colocasia odora attains its maximum temperature at noon. The production of heat in Arum italicum, according to Saussure, attained its maximum from 4 to 7 p.m.

Brongniart gives the following results of his observations on Colocasia odora as regards the time and degree of maximum heat:

| Date of Observation | Hour of Max. Temperature | Temperature of Air | Temperature of Spadix | Temperature above Air | |---------------------|--------------------------|--------------------|-----------------------|----------------------| | March | 14 | 76-1° F. | 84-2° F. | 81° F. | | | 15 | 75-2° | 93-2° | 18 | | | 16 | 74-8° | 93-2° | 18-4 | | | 17 | 75-2° | 93° | 19-8 | | | 18 | 80-6° | 93-3° | 14-8 | | | 19 | 77-9° | 82-4° | 4-5 |

The rise of temperature bore an evident relation to the development of the stamens and the emission of the pollen, and after the latter had taken place, the temperature fell and the spadix withered.

Garreau made observations on the heat given out by the spadix of Arum italicum. In an experiment conducted on 8th June 1851, the atmospheric temperature being 66-2° F., he found that the mean heat per hour was 11-2° F., the mean of the oxygen consumed 766, and its mean volume, when compared with the organ as unity, was 16-9. The oxygen consumed during the 6 hours of the paroxysmal heat was 460 cubic centimetres, and that consumed during the 18 succeeding hours was 230, making in all, in 24 hours, 690 cubic centimetres. The quantity of oxygen consumed increased with the temperature. In three distinct experiments the results were—

| No. 1. Mean heat, 9-6° F. Oxygen consumed, 10-1 cubic cent. | | No. 2. — 11-2 — 16-9 — | | No. 3. — 13-1 — 17-3 — |

Garreau says that the nature of the surface of the spadix of Arum seems to facilitate absorption. It consists of numerous projecting cells, giving a velvety appearance to the organ, with two or three open stomata. Saussure found that the blossom of Arum maculatum, when cold, consumed five times its volume of oxygen, but when warm, thirty times. In a flower during the paroxysm, he found that the spathe consumed five times its volume of oxygen, the bare portion of the spadix 30 times, and the part covered with flowers 132 times.

The relation which the evolution of carbonic acid bears to the heat produced is thus shown by Dutrochet:

| Name of Organ | Mean Temp. above Air in 12 Hours | CO₂ evolved in 24 Hours | |---------------|----------------------------------|------------------------| | Spathes of Arum maculatum | 0-06° F. | 1-0 | | Spadix of do. | 18-00 | 28-0 | | Male organs of do. | 12-00 | 13-0 | | Female organs of do. | 2-7 | 1-0 | | Female flower, Guard | 0-16 | 7-6 |

The quantity of carbonic acid evolved is in direct proportion to the oxygen absorbed, and the degree of chemical action which takes place determines the amount of heat.

The presence and contact of oxygen gas is necessary for these phenomena. When the spadix of an Arum is put into oxygen gas, the heat is developed rapidly and powerfully, the maximum difference between the heat of the oxygenated spadix and another in the air varying from 5° to 12° F.; and when the spadix is placed in carbonic acid gas or nitrogen, the evolution of heat ceases. The production of heat is prevented by covering the spadix with olive oil, grease, tallow, honey, or starch.

Periods of Flowering.—The age at which different species of plants produce flowers varies. Some spring from seed and produce flowers in the course of a single year and die, others produce flowers the second year after germinating and then decay, while a third set continue to flower for many years in succession. Hence the division into annual (O), biennial (Z), and perennial (Z), plants. In some cases flowering is long delayed, and when it does occur the development of the flowering stalk takes place with great vigour and rapidity, and the plant dies after producing fruit and seed. Any cause, whether natural or artificial, which retards flowering, is attended with results of a similar kind more or less marked. When fruit trees have been in a non-flowering condition, they sometimes suddenly produce abundance of blossoms. A season in which blossoming has been scanty is often succeeded by one in which it is profuse. When the flower-buds are taken off early, it sometimes happens that an annual plant, such as Mignonette, is rendered biennial or perennial. The tree Mignonette is pro- duced in this way. When plants grow in a rich soil it sometimes happens that, in place of producing flowers, they develop branches and leaves luxuriantly. In these instances cutting the roots, pruning the branches, taking a ring of bark out of the stem so as to retard the descent of sap, and transplanting into poor soil, frequently cause the plants to flower. Injuries inflicted on forest trees late in the season sometimes give rise to autumn flowering. When a branch is grafted on a vigorous stock it often happens that its flowering is accelerated. By this process a check is put to luxuriant branching, and the sap of the old stock stimulates the young graft or scion.

The different periods of the year in the various countries and climates of the globe are marked by the flowering of certain species of plants. Each climate has its peculiar floral calendar. Thus in Scotland we have the Winter Aconite (Eranthis hyemalis) and the Snow-drop (Galanthus nivalis) flowering in February, the Primrose (Primula vulgaris) in March, the Cowslip (Primula veris) and Daffodil (Narcissus Pseudo-Narcissus) in April, the Hawthorn (Crataegus Oxyacantha) in May, numerous successive species expanding their blossoms during each month of summer, the Ivy (Hedera Helix) flowering in September, and the autumn Crocus (Cochleum autumnale) pushing up its flowering-stalks in October. Every month and every week has thus its peculiar flowers. The expansion of certain flowers indicates the revival of vegetation after winter in temperate and cold regions, and after the dry season in warm countries.

The time of expansion of the flowers of the same species in different countries gives indications in regard to the climate; and the difference of seasons in the same locality is also marked by the dates at which the same species flower. The registration of the periodical phenomena of flowering or florescence is suggested by the British Association as one of the points to be attended to in determining the nature of different seasons. In 1829 Schubler states that the Lily of the Valley (Convallaria majalis) flowered at Rome on the 26th April, at Tubingen on 10th May, at Berlin on 17th May, and at Greifswald on 10th June. According to Berg- haus the same species flower at Zurich 6 days later than at Parma, at Tubingen 13 days later, at Jena 17, at Berlin 25, at Hamburg 33, at Greifswald 36, and at Christiania 52. The Almond is said to flower at Smyrna early in February, in Germany at the beginning of April, and in Christiania not till the commencement of June. There is thus periodicity in flowering as regards the seasons, and plants retain the tendency to expand their flowers at a definite period of the year even when transported to countries where the seasons are reversed. In these circumstances they do not immediately accommodate themselves to the opposite conditions of the seasons in which they are placed, but for a while continue to show symptoms of flowering at the usual time to which they were accustomed in their native clime. Some varieties flower earlier than others of the same species. This has been noticed in the case of species of Thorn, Horse-chestnut, and many other plants. By means of slips taken from such plants gardeners perpetuate early flowering varieties.

Temperature is a most important agent in causing plants to flower, but in each species the range of flowering-temperature is definite. A high temperature, in the case of plants belonging to cold regions, often makes them produce leaves in place of flowers, or if flowers are produced, they drop off and are abortive. Fruit trees of temperate regions, when grown in tropical countries, are frequently unproductive. In cultivating plants in hot-houses, it is of importance to regulate the temperature, and at the same time to attend to the state of moisture and ventilation, if we wish the plants to flower properly.

There are differences in regard to the hours of the day at which flowers expand. Some open at dawn of day, others a few hours later, others at mid-day, others in the evening, and a few after darkness has come on. Roemeria violacea expands its blossoms early in the morning, and the petals have generally fallen off two or three hours before noon. Many Composite plants, as Chicory (Fig. 375), show a remarkable tendency to open and close their florets. Species of Goat's-beard (Tragopogon) receive the common name of go-to-bed-at-noon on account of closing their florets at mid-day. Ornithogalum umbellatum (Fig. 376) is called Lady-Eleven-o'Clock, on account of its flowers expanding about that hour in the forenoon. Enothera biennis is called Evening Primrose from opening its flowers in the evening. The vigils of plants attracted the attention of Linnaeus, and he constructed what he called a Floral Clock, in which the hours of the day were indicated by the opening of certain flowers, and which were hence called horological.

Fritzsch has paid particular attention to the opening and closing of flowers, and gives the results of observations made at Prague, in Bohemia. He states that these phenomena are rarely momentary, but that they are slow and continuous processes, which at all hours of the day are in varying degrees of intensity. He examined 140 species of plants belonging to 29 natural orders, and found that the phases exhibited by flowers in regard to sleeping and waking are influenced by light, by temperature, and more especially by insolation or exposure to the direct rays of the sun. They are also, in a certain degree, dependent on colour.

Although there seems to be no time of day when the blossoms of certain plants do not open, yet in the greater number of cases they are closed soon after sunset. The number of species which begin to awake increases slowly at the early hours of the morning, then more rapidly from 2 A.M. to 7 A.M., and decreases again rapidly after mid-day. After that hour only those species open which are night-bloomers. With the exception of a few hours about midnight there is no hour of the day at which blossoms do not begin to close; there are, however, only a few about mid-day, from which time the number increases, reaching its maximum at 6, and then again decreasing.

When blossoms begin to open after the cessation of sleep, the change usually takes place in the first instance slowly, then more rapidly, and, as it approaches its maximum there is another retardation. In a few plants only the complete expansion lasts an hour, more commonly not so much; they then begin to close again, at first slowly, afterwards more rapidly, and, as they approach the maximum of approxima- tion of their petals, the progress is again slow. The flower remains many hours in a more or less closed condition, until the time returns for a new cycle of phases. The state of expansion of the corolla varies. In some cases the limb spreads out at a right angle with the tube, in other cases the angle is less, while in some the limb is turned down so as to form an oblique angle with the tube.

The time of the greatest expansion of the flowers varies in different species. In general the number of species whose blossoms attain the maximum of their phase increases from sunrise to mid-day, and then decreases till sunset. None of the day-bloomers are open till 7 A.M., or later than 5 P.M. A similar law seems to hold good with the night-bloomers, which generally seem to open their corolla fully towards midnight, while at mid-day they are completely closed. In those blossoms which are fully expanded in the morning, the duration of expansion is short. In those blossoms which expand in the afternoon, the condition of waking is limited by the length of time the sun is above the horizon. In those blossoms which are fully expanded in the night, the duration of sleep is shortest. Those blossoms which are fully expanded in the morning open in general more rapidly than they close, while in those which open in the afternoon the contrary law prevails. While the time of sleep of plants is in close connection with the apparent daily course of the sun, the degree of expansion depends on the temperature of the air and various meteoric conditions, as well as on insolation or exposure to the direct rays of the sun.

Exposure to artificial light causes some flowers to expand. The flowers of Crocus have opened under the light of an Argand lamp, those of Gentiana verna expanded fully when exposed to the light of a gas-burner. Gloomy weather and rain cause flowers to close. Those which are very sensitive to such influences are called meteoric. There is a periodicity in flowering which is not easily interrupted. If a plant is accustomed to flower in daylight at a certain time, it will still make an effort to expand its flowers at the wonted time, even when confined in a dark room; showing that light is not the only cause of the expansion. As regards the connection between the colour of flowers and their expansion, Fritzsch says that yellow blossoms possess the strongest tendency to contract and expand, then follow white, red, and blue.

The direction and position of the flowers on their stalks appear in some cases to be controlled by the sun's rays. This is particularly the case in Composite plants. The capitula of some of them are erect during the day, and droop at night. Species of Hypochaeris are said to incline their heads towards the quarter of the heavens in which the sun is shining. The name Sun-flower (Helianthus, Girasole) was given to a genus of Composite plants on account of the supposed influence of the sun on the direction of their heads. In Victoria regia there is a spontaneous motion of the flower and the flower-stalk, the cause of which appears to be very obscure.

Occasionally movements of irritability are observed in petals. Morren observed them in the labellum of some Orchids, such as Megachilium falcatum, and they have been noticed also in the stalk of the labellum of Drakaea elasticus, which bends in a hinge-like manner when irritated. Various species of Pterostylis, and many Bolbophyllums, especially B. barbigerum and B. Careyanum, show labellar movements. In Caleana nigrita, a Swan River Orchid, the column is a boat-shaped box, the lid of which is formed by the labellum. The latter is hinged on a claw, which reaches the middle of the column; when the flower opens the labellum turns round within the column and falls back, so that, the flower being inverted, it stands fairly over the latter; whenever an insect touches its point the labellum makes a sudden revolution, brings the point to the bottom of the column, and thus imprisons any insect which the box may contain. If an insect is caught, the labellum remains shut; but if there is no insect, it recovers its position. The labellum of Spicula ciliata is also moveable.

Colours of Flowers.—The colours of flowers naturally attract the attention of all, and their varied hues are in an especial manner an object of interest to the florist. These colours usually reside in the corolla, but in the case of many plants, especially Monocotyledons, they occur both in the calyx and corolla (perianth); and in some instances, as in Salvia and Amberstia, the bracts are highly coloured. The changes produced by culture on the colours of many plants are familiar to every one, and they may be well illustrated in the case of the Tulip and Dahlia, the flowers of which are naturally of a yellow colour, but in the hands of the florist assume all varieties of red, white, and yellow. From its variable nature, colour is not taken much into account by the practical botanist in the determination of the species of flowering plants. It is chiefly in Cryptogamic plants, such as Fungi and Seaweeds, that this character is regarded of value. It is probable, however, that too little attention has been paid to this subject, owing to the want of an accurate nomenclature, such as has been adopted by Werner in the characters of minerals.

In reference to their colours, flowers are divided by De Candolle into two series—1. Those having yellow for their type, and which are capable of passing into red and white, and never into blue. 2. Those having blue for their type, and capable of passing into red and white, but never into yellow. The first series is called Xanthic, the second Cyanic. The following is a tabular view of the two series, green being considered as an intermediate state of equilibrium between the two:

| Red | Orange-red | Orange | |--------------|------------|--------| | Yellow-orange | Yellow | Yellow-green |

Xanthic Series.

| Green | Colour of Leaves | |--------------|------------------| | Blue-green | Blue | | Blue-violet | Violet | | Violet-red | Red |

Cyanic Series.

Green, which is made up of blue and yellow, is the centre whence the two series diverge, and they meet again in red. It would appear that all flowers capable of changing colour do so in general by rising or falling in the series to which they belong.

The original colour of the Tulip is yellow, and although by cultivation it is made to assume all the varieties of colour in the yellow series, we do not find it becoming blue. Such is also the case with the common Dahlia and the Rose. No one has succeeded in getting a blue variety of either of the latter. The Geranium, on the other hand, although it presents all shades of blue, red, and white, does not become yellow. There seems thus to be a certain limit in the range of colour which a species can be made to assume. These remarks apply only to the change of colour in a given species. They will not apply in all cases to every species of a genus. Thus, while most of the Gentians belong to the blue series, and do not become yellow by cultivation, there is a yellow species of the genus (Gentiana lutes) which never changes into blue. Again, we find certain plants exhibiting, in the same flower, blue and yellow colours. This is seen in Dendrobium sanguinolentum; also in Pansies, and in many other parti-coloured flowers, as in Convolvulus tricolor, and in species of Myosotis, which have a yellow zone round the corolline tube, while the upper part is blue. In these last mentioned cases each of the coloured portions of the flower vary in general only in their proper series—the part which is yellow never becoming truly blue, nor the blue yellow. The florets of the ray of Composite plants often exhibit blue colours, while those of the disk are yellow. The law by which the changes of colour are regulated has not been ascertained, and it is impossible, in the present state of our knowledge, to predict what colour a florist's flower will assume. The different rays of light have different effects as regards colours. It would appear, also, that the nature of the soil sometimes alters colours. Thus, Hydrangea hortensis (Hortensia speciosa) produces blue in place of pink flowers, when planted in some kinds of bog earth and of yellow loam. The colours of flowers often appear to depend on the state of oxygenation of the juices. Certain flowers have a pale hue when first produced, and change under the influence of sunlight. The colouring matter of flowers is usually of a fluid nature, and has not the composition of chlorophyll.

The arrangement of coloured flowers in the parterre is a matter deserving the attention of gardeners. Chevreul has written very fully on the subject. He states that an important principle is to combine such colours as produce white light. Thus red, blue, and yellow, form, by their union, a white ray. Hence flowers of these colours may be, with propriety, placed together; or a flower of one of these primary colours may be combined with one whose colour is made up of the other two in the shape of a binary compound. Thus, red agrees well with green, which is made up of yellow and blue. This may be seen in the case of the scarlet Pelargonium, where the colour harmonizes with its own green leaves, or with the green of other plants around it; so also in the case of red Dahlias. Again, blue harmonizes with orange compounded of yellow and red, as may be illustrated by a combination of the Brachycome Iberidiflora with Erysimum Perofskianum. Yellow harmonizes with violet, composed of blue and red, as seen in the petals of Pansies. To produce the best effect the colours should be as nearly as possible of the same tone. In cases where colours do not agree, placing white between them restores the effect.

Odours of Flowers.—The odours of flowers, as well as their colours, vary much. The sources of odours in flowers are very obscure. They are often traced to the presence of fragrant volatile oils or resins. The effluvia are of such a subtle nature as to elude chemical analysis. They are usually developed under the influence of sunshine, but in certain instances odours are emitted during the absence of light. Some flowers are only odoriferous in the evening. This is the case with Cestrum nocturnum, with several species of Catatatum and Cymbidium, and with Lychis vespertina. Certain flowers, such as Hesperis tritis, and Nectanthes arbor tritis, receive their specific names (tritis, sad) from giving out their fragrance only at night.

The exudation of odours by nocturnal flowers sometimes takes place in a peculiarly intermittent manner. Thus in the night-blooming Cereus (Cereus grandiflorus) the flowers are fragrant only at intervals, giving out puffs of odour every half hour, from eight in the evening till midnight. Morren states that on one occasion the flower began to expand at six o'clock in the evening, when the first fragrance was perceptible in the hothouse. A quarter of an hour afterwards the first puff of odour took place, after a rapid motion of the calyx; at 6:23 there was another powerful emanation of fragrance; by thirty-five minutes past six the flower was completely open; at a quarter to seven the odour of the calyx was the strongest, but modified by the petals. After this time the emanations of odour took place at the same periods as before. The odours of flowers have frequently peculiar effects on nervous individuals, particularly when the odours are connected with the presence of hydrocyanated oils. The odour of some flowers is remarkably overpowering, and that of others, such as Stapelias or Carrion flowers (Fig. 377), is very offensive.

II.—PHYSIOLOGY OF THE ESSENTIAL ORGANS OF REPRODUCTION.

1. Sexuality of Plants. Maturation of the Organs concerned in Reproduction; and changes preceding the Development of the Embryo.

The idea of the existence of separate sexes in plants was entertained in early times, long before separate male and female organs had been demonstrated. The production of Dates in Egypt, by bringing two kinds of flowers into contact, proves that in very remote periods some notions were entertained on the subject. Female Date Palms only were cultivated, and wild ones were brought from the desert in order to fertilize them. Herodotus informs us that the Babylonians knew of old that there were male and female Date-trees, and that the female required the concurrence of the male to become fertile. This fact was also known to the Egyptians, the Phoenicians, and other nations of Asia and Africa. The Babylonians suspended male clusters from wild Dates over the females; but they seem to have supposed that the fertility thus produced depended on the presence of small flies among the wild flowers, which, by entering the female flowers, caused them to set and ripen. The process was called palmification. A similar statement was made in regard to the Fig. The process of caprification, or bringing wild Figs in contact with cultivated ones, so as to cause the latter to ripen soon, is mentioned by Aristotle, who observed that a certain insect was generated on the flowers of the Caprifig (wild Fig), which, having become a fly, entered the unripe fruit of the domestic Fig, and caused it to set.

Grew, in a paper on the Anatomy of Plants, read before the Royal Society in November 1676, seems to have been the first who really observed the functions of the stamens and pistils. Up to this period all was vague conjecture. Grew speaks of the attire, or the stamens, as being the male parts, and he mentions having spoken of the subject to Sir Thomas Millington, Sivilian Professor at Oxford, who entertained the same opinion. Ray adopted Grew's views, and states various arguments to prove their correctness in the preface to his work on European Plants, published in 1694. In 1703, Mr Samuel Morland, in a paper read before the Royal Society, stated that the farina (pollen) is a congeries of seminal plants, one of which must be conveyed into every ovum or seed before it can become prolific. In this remarkable statement he seems to anticipate in part the discoveries afterwards made as to pollen tubes, and more particularly the views promulgated by Schleiden. In 1711, Geoffroy, in a memoir presented to the Royal Academy at Paris, supported the views of Grew and others as to the sexes of plants. Linnaeus was the next botanical author who took up the subject of the sexes of plants, and he may be said to have opened a new era in the history of Botany. He first published his views in 1736, and divided plants into sexual and asexual, the former being Phanerogamous or flowering, and the latter Cryptogamous or flowerless. In the latter division of plants he could not detect stamens and pistils, and he did not investigate the mode in which their germs were produced. He was no physiologist, and did not promulgate any views as to the embryogenetic process.

Soon after the promulgation of Linnæus' method of classification, the attention of botanists was directed to the study of Cryptogamic plants, and the valuable work of Hedwig on the reproductive organs of Mosses made its appearance in 1782. He was one of the first to point out the existence of certain cellular bodies in these plants which appeared to perform the functions of reproductive organs, and to them the names of antheridia and pistillidia were given. This opened up a new field of research, and led the way in the study of Cryptogamic reproduction, which has since been much advanced by the labours of numerous botanical inquirers.

In 1815, Treviranus roused the attention of botanists to the development of the embryo, but although he made valuable researches, he did not add much in the way of new information. In 1823, Amici discovered the existence of pollen-tubes, and he was followed by Bronnian and Brown. The latter traced the tubes as far as the nucleus of the ovule. These important discoveries mark a new epoch in Embryology, and may be said to be the foundation of the views now entertained by physiologists, which have been materially aided by the subsequent elucidation of the process of cytotogenesis, or cell-development, by Schleiden, Schwann, Mohl, and others. The whole subject has been investigated recently with great assiduity and zeal by physiologists, both as regards Cryptogamous and Phanerogamous plants. The formation of germinal vesicles in the ovule, and the development of the embryo in flowering plants, have been fully considered by Schleiden, Mirbel, Mohl, and others; the embryogenetic process in Coniferae plants and in the higher Cryptogams by Hofmeister, Suminski, and Mettenius; and that of the lower Cryptogams by Thuret, Decaisne, and Tulasne. We have thus been enabled to come to certain general conclusions on this obscure subject, and future observers have been directed in the proper path of investigation.

In flowering plants the organs concerned in reproduction are the stamens and pistils, while in flowerless plants, organs called antheridia and archegonia, as well as peculiar cells, exist, which appear to perform this function. As regards the former class of plants, many proofs have been given that the pollen discharged from the anthers must be applied to the stigmatic surface of the pistil in order to produce perfect seed. Among the best evidences of the functions of the stamens and pistil in flowering plants, are those derived from species in which these organs are separated, and in which, when contact is carefully prevented, no seed is produced. Experiments of this kind require much caution to avoid fallacy arising from pollen being waited from a distance, so as to cause female plants to produce fruit. Moreover, it sometimes happens that in plants usually producing pistilliferous flowers only, stamens are developed. Such a case might be considered, by careless observers, as an instance of a female plant producing fertile seed without the action of pollen. When flowers are completely double, that is, when the stamens and pistils are entirely converted into petals, no seed is produced. Occasionally, however, in flowers apparently double, a single stamen may exist, with sufficient pollen to fertilize the plant, or the pistil may be perfect, so that pollen from other plants may affect it, and lead to the production of perfect seed. In certain instances, it has been stated that perfect seed has been produced without the agency of pollen. But the cases require further investigation. Henslow has conjectured that cases where fertile seed is stated to have been formed without the action of pollen, may be analogous to what is seen in Aphides, where one impregnation is sufficient to produce eight or ten generations.

In Phanerogamous plants provision is made for securing the application of the pollen to the stigmatic portion of the pistil or to the ovule. The relative lengths of the stamens and pistils, in erect and pendulous flowers, are varied on this account, and the mode in which the anthers open is also made subservient to the same end. In the case of some plants, the elastic filaments are bound down by the floral envelopes until such time as the pollen is ripe, and then they are set free so as to scatter the pollen with great force. This phenomenon is seen in the common Nettle (Urtica dioica), and in the Pelitory of the wall (Fig. 378). In the species of Kalina a similar phenomenon is observed, the anthers being held for a time in little pouches or sacs of the corolla, and then moving with a jerk towards the pistil.

In the Barberry (Fig. 379), the filaments are very irritable on their inner surface, at the point where they join the receptacle, and when touched in that situation they move towards the central organ. The motion, like that of the leaves of the Sensitive plant, seems to be connected with a small cellular swelling or gland at the base. In species of Stylium (Fig. 380), the stamens and pistil are united in a common column, which is jointed and irritable, and which, when touched at the joint, passes with force and rapidity from one side of the flower to the opposite one, so as to burst the anthers and scatter the pollen on the central stigma. The stamens of the common Rock-rose (Helianthemum vulgare), and of species of Cistus, exhibit movements which are apparently connected with the application of the pollen. In Parnassia palustris (Fig. 381), and in Rue, the stamens move forward in succession towards the pistil.

Bees in collecting the honey secreted at the base of the petals are made instrumental in applying the pollen to the stigma. In Orchids, in which the anthers are placed on the upper part of a column with the stigmatic surface separated from them, and the pollen is in masses (Fig. 265), the agency of insects seem to be required for fertilization. The flowers of these plants exhibit remarkable animal forms, probably with the view of attracting insects. The flowers also secrete a large amount of saccharine matter, and are odoriferous; their pollen-masses are very easily detached. All these circumstances seem to be connected with their mode of impregnation. In Asclepiadaceae, which have Botany also peculiar pollinia (Fig. 382), insects are attracted by the odor of the flowers, which is sometimes very fetid, as used successfully after 18 years. Pollen may be carried to a distance and retain its fertilizing power.

The quantity of pollen produced in some cases is enormous. In the case of Firs and Pines, this seems to be connected with the fact that the cones or female organs are separate from the staminal clusters, and that, moreover, the leaves are usually evergreen, and thus present an obstacle to fertilization. The yellow powder in Pine forests falls to the ground in vast quantity, and it is sometimes carried by the winds to a great distance, so as to fall in the form of what have been called sulphur showers. Morren counted the number of pollen grains in a plant of Cereus grandiflorus which grew in the stove of the Botanic Garden of Liège. He found that in each flower there were 500 stamens, and as 40 flowers were produced, the total number of stamens on the plant was 20,000, and of pistils 40, each having 24 stigmas. Each anther contained 500 pollen grains, and hence the total number of grains in each flower was 250,000, and upon the entire plant 10,000,000. In many catkin-bearing plants, which are monococious or dioecious, the pollen is abundant, and the essential organs are developed before the leaves are produced. Examples of this occur in the common Hazel, and in Willows.

Observations have been made by Gaertner and Köhler as to the quantity of pollen required to fertilize the ovules. One grain, or at most three, are sufficient to impregnate the ovule of Mirabilis longiflora and M. Jalapa. In a single flower of Hibiscus Trionum, Köhler counted 4863 pollen grains, and he ascertained that 50 or 60 were sufficient to fertilize all the ovules in the ovary, usually amounting to 30; when fewer grains were employed, impregnation was not complete; thus 25 grains only impregnated from 10 to 16 ovules. In most cases the pollen of a single fertile anther is sufficient for the perfecting of the ovules, and the additional anthers are produced with the view of insuring the result. Morren states, that in the flower of Cereus grandiflorus he found 150,000 grains of pollen, out of 250,000, which had not been applied to the stigma, while the number of ovules in each ovary was about 30,000.

During the evolution of the stamens and the maturation of the pollen, the pistil undergoes changes, more especially as regards the stigma, which becomes enlarged, lax in its texture, and covered with a viscid secretion. In species of Campanula, during the discharge of the pollen, the style, which is covered with hairs (Fig. 384), elongates, and in

in Stapelia (Fig. 377), as well as by saccharine matter. In various species of Birthwort (Fig. 383), in which the essential organs are contained in a tubular perianth, insects are employed to effect the application of the pollen. Species of Tipula enter the expanded portion of the perianth, and then crawl down through the long tube to the cavity at the base containing the stamens and pistil. On attempting to return they are prevented from getting out by numerous hairs pointing downwards, which act like a trap. While moving about in the lower chamber, the insects spread the pollen when ripe, and afterwards when the flower fades they escape.

Pollen grains in general require to be protected from the direct action of moisture, which causes them to burst prematurely. The closing of flowers during rain accomplishes this object. In the Daisy and other Composite plants the outer florets close over the inner ones, and thus prevent injury from wet. When plants grow in water the pollen is sometimes of a peculiar nature, and the anthers are placed along with the pistils in a covering to protect them from the effects of moisture. In other aquatics, the peduncles rise above the water at the time when the flowers are developed. In Vallisneria (Fig. 22), the female plant, b, sends up a long spiral peduncle, which sometimes increases in length 14 inches during twenty-four hours, and which enables the flower to appear above water, and to be accommodated to its depth, at the same time that the root remains attached to the mud below; the male plant, a, on the other hand, is detached from the bottom of the water, floats on the surface, and there perfects its pollen, which is ultimately wafted on the pistilliferous plant.

The fertilizing power of the pollen is retained for a different length of time in different species of plants. According to Köhler and Gaertner, the pollen continued fresh in some species of Tobacco only for 48 hours; in Datura Stramonium, D. Tatula, and D. ferox, and in Lychins dioica for 2 days; in Hibiscus Trionum and the Clove-pink for 3 days; in Lobelia syphilitica and L. splendens for 8 or 9 days; in Wallflower for 14 days; in Orchis abortiva for 2 months. The pollen of the Hemp, Tea, and Camellia, has been kept fresh for a year; and Michaux mentions the pollen of Chamaecrops humilis and of the Date as having been Botany.

anisophylla, the style has a curved stigmatic apex, which gradually becomes straightened so as to come into contact with the hairs of the corolla on which the pollen is scattered. The stigma in species of Mimulus, is bilamellar, and the two lamellae close when touched with pollen or any extraneous body.

Before the process of impregnation, certain changes also take place in the ovule. The relative position of its parts is frequently altered, so that the micropyle is brought near to the placenta (Fig. 385). Moreover, one of the central cells becomes much enlarged and developed, so as to form the embryo-sac (Fig. 386, s). At the end of this sac, next to the micropyle, several delicate free nucleated cells are produced, to which the name of embryo-vesicles or germinal-vesicles has been given (Fig. 386, c). In this way the ovule is prepared for the action of the pollen, and for the production of the embryo plant.

The essential organs, when performing their active functions, absorb much oxygen and evolve carbonic acid. At the same time they acquire a certain elevation of temperature. This has been already noticed when speaking of the floral envelopes. The time of the emission of pollen seems to be that at which the maximum heat is produced, and the stamens have a higher temperature than the pistil. When the stamens and pistil are mature the anther bursts (Fig. 387), and scatters the pollen, p, on the stigma (Fig. 388, styg). There it is detained, and is acted on by the viscid secretion, by means of which tubes are developed from the intine (Figs. 269 and 390, 2). This is a sort of germination of the pollen cell. These tubes pierce the stigmatic tissue, and convey the fovilla (Fig. 389, f), through the canal of the style to the ovule. In Figure 390, 1, the ovary, o, with the ovule, n, and embryo-sac, er, is represented; the pollen, p, is applied to the stigma, styg, and its tubes, tp, pass through the conducting tissue of the style, styl, to reach the embryo-sac.

The emission of tubes sometimes commences half a minute after the pollen has been applied to the stigma; in other cases, as in Mirabilis Jalapa, it takes from 24 to 36 hours. In the Larch Geleznoff says that the tubes do not emerge for 35 days. The length to which the tubes extend is often very great. In Cereus grandiflorus, Morren estimated that the tubes when they reached the ovary extended as far as 1150 times the diameter of the pollen grain; in Crinum amabile, Hassall says they reach 1875 times the diameter of the grain, in Cleome speciosa 2719 times, in Oxyanthus speciosus 4489 times, and in Colchicum autumnale 9000 times. The length of time which the pollen tube takes to traverse the conducting tissue of the style varies. The time does not always correspond with the comparative length of the style. In some short-styled plants the time taken is very long; while in the case of the long-styled Cereus grandiflorus and Colchicum autumnale a few hours is sufficient. In the case of some Coniferous plants, as Pinus sylvestris, Pineau states that a year elapses before the tubes reach the embryo-sac.

2. Embryogeny in Cryptogamic or Acotyledonous Plants.

In the simplest Cryptogamic plants, composed of a single rounded cell, as in the Red-snow plant (Fig. 56), the processes of reproduction and nutrition cannot be separated. The same cell appears to perform both functions. At a certain period of growth divisions take place in the cell-contents, and, by the bursting of the parent cell, germs are discharged which are capable of producing new individuals. As we ascend in the scale the plants become more complex. In place of one cell they consist of several united together either in a single or branched linear series, and combined both end to end and laterally, so as to form cellular expansions. In this state the nutritive and reproductive cells are often separate and distinct, as may be seen in common Mould, and in Fungi generally. In Conifers (Fig. 19) and in Diatomaceae (Fig. 13) the existence of reproductive cells with distinct functions has been observed. In many of them we perceive at certain stages of growth cells united by a process of conjugation, the result of this union being the production of a cellular embryo or spore (Fig. 391, e). This conjugation is a very interesting process, and tends to throw light on the subject of reproduction throughout the whole vegetable kingdom. The cells in these plants have in their interior a granular endochrome, which appears to have different functions in the different cells. When certain cells are brought into contact, tubes are emitted which unite the two (Fig. 391, b), the endochromes come into contact, and the result is the formation of a spore, the mixed endochromes being surrounded with a proper membrane. Sometimes the contents of one cell considered as the male pass into the other in which the spore is produced, as in Zygnema, and sometimes the contents of both cells unite, and the spore is produced in the tube between them, as in Diatoms.

In many of the Conifers, however, spores appear to be produced without the conjugation of separate filaments. In such instances it is conjectured that different cells in the same filament perform different functions, and are so placed that at a certain period their contents by coming into contact develop a germ. The same filament may thus contain both male and female cells; although botanists as yet have not been able to show the difference between them. In some species of Melosira the endochrome at each end of the cell appears to have a different property, and mixture takes place in the cavity of a single frustule. In this case there is a movement towards the centre of the cell when the spore is formed. Proceeding to other divisions of Acotyledons, we find different kinds of reproductive organs, which can, however, only be observed at certain periods of development, and frequently cannot be seen after the embryo has been fully formed. In the same way as in the flowering plants, when the seed has been ripened the stamens have generally withered and fallen off, and sometimes also the style and stigma. It is of importance, therefore, in all investigations into Cryptogamic reproduction, to examine the plants at their early period of growth. The reproductive organs have received different names in different natural orders of Cryptogams. They are generally called antheridia and archegonia or pistillidia, from their supposed analogy to anthers and pistils. The antheridia contain sperm-cells, in each of which is a moving ciliated phytozoon, spirillum, or spermatozoid, and the pistillidium or archegonium contains a germ-cell or embryonal cell, which produces a germinating body.

Spermatozooids are considered as analogous in their function to the spermatozoa of animals. They have been traced to the archegonia, or the cells in which the rudimentary embryo is formed. Hofmeister states that he has often seen spermatozooids swimming about around the archegonium, in longitudinal sections of the involucres of Jungernannicce (Fig. 392); he has also seen them in a motionless state after the rudiment of the fruit began to be developed. Similar observations have been made in regard to Mosses and Ferns; and Suminski is disposed to think that the extremity of a spermatozoid in Ferns is developed as an embryonic cell, in the same way as Schleiden thinks the end of the pollen tube constitutes the first cell of the embryo in flowering plants. Thuret has observed in dioecious Fuci, that the embryo-cell in the archegonium was not developed as a germinating body, when the antheridian cells were kept separate. After the application of the contents of the antheridia to the archegonia, a cellular body is produced in the latter, which may be called a sporoid embryo. This cell may be discharged at once, or it may go through certain phases of existence without being separated from the plant on which it is produced.

In Mosses there is a free germ-cell (embryonal cell) at the base of the archegonium. Spermatozooids, from the sperm-cells of the antheridium, reach it in all probability, and then it is developed into the sporangium or spore-case (Fig. 393), which is the second generation of the plant, according to some authors. The spores produce the leafy plant, bearing antheridia and archegonia. In Figure 394 is shown the confervoid prothallium, p, of a Moss produced from the spore, and bearing buds, a, b, which produce leafy individuals with organs of reproduction. After the contact of these organs, a single cell of the archegonium is developed into the complete fruit (theca or sporangium) which is often borne upon a stalk (Fig. 398). The complete fruit contains spores, which, when discharged, again develop the foliaceous plant. Bruch and Schimpfer say that Mosses having antheridia and archegonia upon the same stem always bear fruit, and that in dioecious Mosses the capsule is not developed unless the plants bearing sperm-cells and those producing germ-cells are in proximity.

In Ferns the prothallium, pro-embryo, or prothallus (Fig. 395), bears antheridia and archegonia at the same epoch. It is produced from the spore, and consists of cells, as shown in Figure 350. The antheridia occur on the under surface of the prothallium, and they consist of a cellular papilla having a central cavity (Fig. 396, a). This cavity contains free cellsules, which are discharged by a rupture at the apex, b, and these little cellsules, in bursting, give exit to a ciliated spiral filament or spermatozoid (Fig. 397), which swims actively in water. The archegonia (Fig. 398) exist on the under side of the prothallium, near the notch of the border. They are less numerous (varying from three to eight), and consist of cellular papillae formed by ten or twelve cells. They are larger than the antheridia, and have a central canal, a, leading down to a large globular cell, c (called by some, ovule), imbedded in the substance of the prothallium or pro-embryo, and containing the embryo germ, e. This canal is closed at first, and then opens. In the globular cell at the bottom of the archegonium, a free cell is first formed, which, it is supposed, is reached by the spermatozooids. After a time this cell divides, and is gradually converted into an embryo, with a bud above and a radicle. below, from which the regular leafy stem of the Fern grows (Fig. 395, f). The life of the sporangiferous plant is indefinite, as in Tree Ferns, while the prothallus is usually of very short duration. Thus in Ferns the spores contained in the sporangium form the prothallus (Fig. 395, p) without impregnation, and this latter process is necessary for the development of the germ (Fig. 398, e), which gives rise to the leafy sporangiferous stem or frond; while in Mosses the spore forms the prothallus and the leafy stem without impregnation, and this latter operation only causes the development of the stalked theca, or spore-producing part of the plant (Fig. 393).

Hofmeister and Mettenius have examined the reproduction of Club Mosses (Lycopodiaceae), and have detected antheridia and archegonia. They find that the small spores of Lycops discharged from the antheridia (Fig. 358), do not produce new plants, but have an office analogous to that of the pollen, namely, to effect the fertilization of a germ produced by the large spore (Fig. 359). The small spores contain cells with spiral filaments or spermatozooids (Fig. 399, c); the other spore emitted from the oosporophyte or sporangium is much larger than the polliniferous spore, and is the analogue of the ovule. The large spore forms a cellular prothallus in its interior (Fig. 400, p), on which archegonia are developed. The process of impregnation is supposed to take place here by the spermatozooids of the small spores coming into contact with the large spore, after the coat of the large spore has burst at its apex, so as to expose the cellular prothallus and its archegonia. The free central cell of the archegonium then enlarges, divides, and elongates into a filament, which grows down into the prothallus (Fig. 401). A suspensor is thus formed, at the end of which is the embryo, e, imbedded in the cellular tissue at the upper part of the large spore. The embryo finally produces its radicle and its bud, which is developed as the leafy frond. In Rhizocarps the antheridia are sacs containing small spores, which emit cells with spermatozooids (Fig. 402). The large spores contained in the sporangia of Rhizocarps produce a prothallus like that of Lycops, in which archegonia appear (Fig. 403). The prothallus usually develops only one central archegonium. To this the spermatozooids get access, and then the development of the embryo takes place.

3. Embryogeny in Gymnospermous Phanerogams.

In Gymnospermous plants, such as Coniferae and Cycadaceae,* impregnation is effected by direct contact between the pollen and the ovule. There is no true ovary bearing a stigma. In the Coniferae the scales covering the seeds are either reckoned as bracts or as expanded ovarian leaves. In Cycadaceae the naked ovules are produced on the margin of modified leaves. In both these orders it is usual to meet with more than one embryo in the perfect seed. In the Coniferae there is also a peculiar delay in the production of the embryo, after the contact of the pollen. The phases through which the embryo passes in the seed may be reckoned as somewhat similar to those observed in the case of Lycopodium. Brown long ago noticed in the albumen of Coniferous seeds semicircular bodies, three to six in number, which he called corpuscles and which are produced before the pollen tube reaches the ovular sac (Fig. 406, d). They are arranged in a circle near the apex, and differ from the mass of the albumen in colour as well as consistence.

Hofmeister gives the following views as to the production of the embryo in Gymnosperms. The ovule of Conifers consists of a short nucleus inclosed in a single integumentum, and having a large micropyle (Fig. 404). In the delicate cellular nucleus there is developed an embryo-sac, b, sometimes more than one, as in the Yew tribe. The pollen grains enter the large micropyle and come into contact with the nucleus, and then send their tubes into its apex (Fig. 405, c). This process sometimes requires several weeks or months. After this the embryo-sac (Fig. 405 b) becomes gradually filled with cellular tissue or endosperm cells, and at the same time enlarges. This development of endosperm cells occupies frequently a long time, especially in the

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*Plate CXXXIV. the pollen tubes resume their growth, pass through the tissue of the nucleus, and reach the outside of the embryo-sac, one over each corpuscle. The tubes then perforate the membrane of the embryo-sac, reach the canal between the four cells, and come into contact with the corpuscle (Fig. 406, d). A cell at the lower end of the corpuscle then enlarges, and forms the embryonal vesicle. A free cell in the vesicle divides into eight cells by vertical and transverse septa, and these together constitute a short cylindrical cellular body (Fig. 407), the pro-embryo, as it is called by Hofmeister. The four lower cells of this pro-embryo, by the elongation of the upper ones (Fig. 408), are finally pushed into the substance of the nucleus. The four elongated pro-embryonic cells (Fig. 409, 1) now appear as isolated suspensors (Fig. 409, 2), and the cell at the end of each suspensor becomes an embryo, g. There are thus four times as many rudimentary embryos as there are corpuscles. Usually one of these only becomes developed as the embryo of the ripe seed.

The view which seems to be supported by the best physiologists is thus given by Henfrey. In Conifers and Cycads, which embrace Gymnospermous plants, the pollen grains are applied to the micropyle of the ovule, without the intervention of a stigma; they then traverse the cells of the nucleus, and reach the embryo-sac. The endospermal cells which fill this sac develop corpuscles consisting of an enlarged cell surrounded by four others, which leave a canal between them leading to the large cell. The pollen tube enters the canal between these cells, and impregnates the large cell of each corpuscle, just as the spermatozoon acts in the case of Ferns. The large central cell then produces four suspensors, each of which presents at its extremity a rudimentary embryo, only one of which becomes fully developed.

4. Embryogeny in Angiospermous Phanerogams.

In regard to Phanerogamous Angiosperms, when the pollen grains are discharged from the anther, they are applied to the stigmatic surface of the pistil, and the viscid fluid there secreted causes a rupture of the exine and the protrusion of the intine in the form of a tubular prolongation (Fig. 269, f), which gradually elongates as it proceeds down the loose conducting tissue of the style. The closed extremity of the pollen tube sooner or later comes into contact with the ovule, and, in some cases, it appears to be met by a tubular prolongation from the ovule itself. When the pollen tube reaches the ovule it proceeds through the foramen or micropyle so as to come into contact with the embryo-sac (Fig. 386, s). Consequently on this is the development of the cellular embryo. The determination, however, of the steps of the embryogenetic process has given rise to disputes among physiologists. Schleiden maintains that the end of the pollen tube enters or introverts the embryo-sac, and becomes the rudimental cell of the embryo, while most physiologists think that the tube merely comes into contact with the sac, in which a germinal vesicle has been previously formed ready for impregnation. Schleiden states that a cell of the nucleus is developed into the embryo-sac (the quintine of Mirbel), seen in Figure 410, s, and that this occurs in all Phanerogamous plants; that the embryo-sac contains a substance which is gradually transformed into cellular tissue, and which ultimately constitutes (when not absorbed by the growth of the embryo) the endosperm or albumen; that the pollen tube can be traced from the stigma to the micropyle in a very large number of plants, and that in Helianthemum denatum he has not unfrequently extracted the pollen tube free, in unbroken continuity, from the pollen grain to the ovule; that the tube next reaches the embryo-sac, s, the walls of which it presses in before it, and thus becomes surrounded by it, although in reality external to it, like the intestines and their peritoneal covering; that in some instances it causes absorption of the walls of the sac and enters it, and that the end of the pollen tube, e, forms the rudiment of the embryo or the germinal vesicle, in which cells are developed from cyto-blasts, while a portion of variable length, at the upper part of the tube, remains as the suspensor or embryophore.

The views of Schleiden, when first propounded, stimulated all vegetable physiologists. The facts were new, and seemed to upset all former ideas as to the nature of the stamens and pistils. Mirbel and Spach, Meyen, Amici, Hofmeister, Müller, Tulasne, and others, entered the field, and the result has been that Schleiden's opinions have not been confirmed. These authors agree in tracing the pollen tube downwards to the ovule, and they maintain that in the embryo-sac there exists one or more vesicles before impregnation, and that one of these vesicles, after the impact of the pollen tube with the embryo-sac, becomes altered and enlarged, so as to form the rudiment of the embryo.

Amici maintains that there exists an embryonic or germinal vesicle before the application of the pollen; that the pollen tube (Fig. 411, f) reaches the upper portion of the the elongation of the upper part in the form of a confervoid filament, which acts as a suspensor of the embryo. Hofmeister has examined the mode of fecundation in species of Génothera, Godetia, and Boisduvalia, and the result of his researches is that he finds an embryo-sac containing at first numerous minute granules floating in a viscid mucilaginous fluid (protoplasma); in the midst of this granular matter certain nuclei appear, which develop cells varying in number from one to three or more (Fig. 412, r). These nucleated cells appear before impregnation; one of them becomes pyriform, and touches the membrane of the embryo-sac by its conical extremity, while its other extremity hangs free in the embryo-sac. This cell is the germinal vesicle—the embryonary vesicle of Amici. The pollen tube, in passing through the micropyle, is often contracted in its diameter. The end of it is expanded when it reaches the embryo-sac, to which it is applied either at the apex or near it (Fig. 412, f). Sometimes the end of the tube, still closed, introverts the sac, as seen in the Figure, or even perforates it, so as to come into contact with the germinal vesicle. In either case an endosomatic action takes place between the contents of the tube and the sac or the vesicle. In consequence of this action, cell-formation begins in one, rarely more germinal vesicles. The vesicle increases, and is transformed into a compound cellular mass, which Hofmeister calls the proembryo. This divides into two by the formation of a septum; the upper part elongates, and forms a seporate cellular suspensor, s, while the lower portion becomes globular, divides into four, and is developed as the embryo, surrounded by endospermal cells, e. Similar observations have been made by Mohl, Tulasne, Henfrey, and others.

The following may be given as a Résumé of the facts ascertained relative to the process of impregnation in Angiospermous Flowering plants. The pollen grains are applied to the stigmatic portion of the pistil, and by the action of the viscid secretion of the stigma a sort of germination commences—often in a few minutes, sometimes not for many hours, by means of which minute tubes are developed from the inner lining of the grains. These tubes, by continuous growth at their ends, are elongated, and pass through the conducting tissue of the style into the ovary—attaining, in some long-styled plants, a length exceeding the diameter of the grain many thousand times. Before the tubes reach the ovary the ovules have undergone changes in their interior; the embryo-sac has become enlarged, so as sometimes to occupy nearly the entire nucleus, and occasionally to project out of the micropyle in the form of an ovular tube or bag. The protoplasmic matter contained in the embryo-sac immediately before impregnation becomes altered, so as to produce endospermal cells. Nuclei appear in the protoplasm at the upper end of the sac next the micropyle. These nuclei, which are usually three, give origin to as many cells, which are termed the germinal or embryonal vesicles, and which are essential for the formation of the embryo. The pollen tube, subsequent to this, reaches the upper part of the embryo-sac, after penetrating through the micropyle and any nuclear cells that may lie between it and the sac.

On reaching the embryo-sac the pollen tube is either arrested or it elongates still more, so that its swollen extremity penetrates latterly between the embryo-sac and the surrounding cellular tissue, or in certain rare instances introverts the embryo-sac, and even penetrates it so as to come into contact with the germinal vesicles. When the end of the tube comes into contact with the sac, it is probable that there is a transudation of the fluid matter of the foovilla, which passes through the membrane of the pollen tube, through the embryo-sac, and through the wall of the germinal vesicle, and thus impregnation is effected. After reaching the sac, the pollen tube begins to decay; its contents acquire a granular, half-coagulated aspect; and it finally disappears by absorption. It usually happens that only one germinal vesicle is impregnated, and in the progress of its subsequent growth it causes absorption of the others; sometimes, however, several are impregnated, and thus there may be a plurality of embryos formed (polyembryony). The impregnated vesicle enlarges, acquires an ovate, cylindrical, or clavate form, constituting the pro-embryo of Hofmeister. The vesicle divides in all cases by a transverse partition into two cells, one above the other; the lower of these produces cellular tissue in its interior, and is sometimes at once transformed into the embryo. At other times, and more frequently, there is a successive production of cells in the pro-embryonic body, so that the upper division of the vesicle forms a confervoid-like filament, the suspensor, while the lower is transformed into a globular cellular mass, which is the rudiment of the embryo. The suspensor is sometimes of great length; it is attached to the radicular end of the embryo, while the cotyledons are formed at the opposite side. In monocotyledons a single sheathing cotyledon is developed; in dicotyledons two opposite leaves, and after their formation the apex produces the terminal bud or plumule. The embryo is thus suspended in an inverted manner in the seed. In the progress of development a marked division takes place between the radicular extremity and the suspensor, and the latter finally shrivels.

5. Hybridization, or the production of Hybrids in Plants.

In connection with the subject of fertilization, the production of hybrids or mules deserves attention. When the pollen of one species is applied to the stigma of another species, so as to effect fecundation, the seeds thus formed give rise to individuals which are intermediate in their characters between the two parents. The plants produced by this heterogeneous fertilization are called hybrids or mules. A true hybrid is a cross between two species, but the term is often applied to crosses between mere varieties, races, or sub-species. The latter sort of crosses have been occasionally denominated sub-hybrids in order to avoid confusion. In hybridizing it is necessary to bring together species which are allied, as, for instance, the species of the same genus, or those of allied genera. It is not, however, easy to determine the plants which can produce hybrids. Many plants which seem to be nearly allied do not inoculate each other. Sagaret failed in his endeavours to fecundate an apple tree by a pear tree, and no one has succeeded in getting hybrids between the gooseberry and currant, nor between the strawberry and raspberry. It is not common to meet with hybrids in a wild state, because there is a much greater likelihood of the pistil being impregnated by the pollen of the anthers beside it, than by that from a distance; and if fecundation has taken place, then pollen applied from other sources has no effect.

It has been found that for successful hybridizing the pollen must be in perfection, and the stigma also must be fully developed. There appears always to be a preference for its own pollen on the part of the stigma. When strange pollen is applied, even in the case of species which hybridize, it does not act so effectually on the ovules as the pollen belonging to the flower. Dichogamous plants, that is, those in which the sexes are separate, are not so susceptible of the influence of strange pollen. This seems to be a provision to guard against hybridity in such cases.

When impregnation takes place between two pure species the characters of the parents never remain pure and unaltered in the formation of the hybrid. In general every part of the new production is modified, so that it presents a decided difference from either of the parents, though resembling the one more than the other. Sometimes the influence of the male predominates, sometimes that of the female. Hybrids occur in which the characters of the parents are intimately blended, so that it is impossible to say to which there is a greater resemblance. Sometimes the number of the organs is curiously intermediate; thus Cucubalus has three stigmas, and Lychnis five, and a hybrid between them has four. Again, hybrids occur in which one part or other approaches the paternal or maternal form, though the characters of the parent never pass altogether pure into the new organism. There is a third set of hybrids in which there is a resemblance to one of the parents, whether male or female, so decided, that the agreement is at once perceptible and beyond doubt.

Hybrids, although they may be fertile at first, rarely continue so for many generations. The cause of sterility in mules has not been fully ascertained. Henslow could not find in a hybrid Digitalis any structural changes which could account for barrenness. Hybrids may be fertilized by pollen taken from one of the parents, and then the offspring approaches in character to that parent. Hybrids impregnated for a third or fourth time with the pollen of the original male plant, approach more and more to the male type. Such is also the case when the impregnation is effected by pollen taken from the original female type, but in this instance the change is usually more slow. Gärtner, to whom we are indebted for most of these remarks on hybridity, gives a tabular view of the number of impregnations requisite to complete changes of species by hybridization. He produced hybrids between the two species named, and then, by using the pollen of the original male or female parent, he found that in progress of time the species are brought back to the male or female type.

Hybridizing is an important horticultural operation. By it the gardener endeavours to increase the size of flowers, to improve their colour, to approximate their forms to some assumed standard of perfection, to enlarge the foliage as in esculents, to render tender plants hardy, to heighten the flavour of fruits, and to exchange early for late varieties. The changes produced by muling on the size and colour of the blossoms are very remarkable. By inoculating Cereus speciosissimus with C. grandiflorus, we find that the immediate result is a seedling whose flowers are ten inches in diameter. The hues resulting, however, from the union are not necessarily intermediate. Blue and yellow do not produce green, as proved by a hybrid between Verbascum phoenicium and V. philomoides. By muling, beautiful varieties have been produced between Rosa indica and R. moschata, Azalea pontica and A. nudiflora coccinea, Rhododendron arboreum and R. caucasicum, catatwiense, ponticum and compannulatum; between Rhodothamnus Chamaecistus and Phyllodoe cervulea, Veronica fruticosa and saxatilis, Cereus speciosus and speciosissimus; also between species of Fuchsia, Mahonia, Potentilla, Pelargonium, Calceolaria, Viola, Dahlia, Erica, Narcissus, and numerous others. In the case of Rhododendrons, gardeners have been able to secure the fine colour of the Indian R. arboreum with the hardiness of the American species. By inoculating the common Heartsease with the large-flowered Pansy of the Altai Mountains, a degree of vigour has been infused into the former which we could not hope to obtain by ordinary means. The fine varieties of Pelargonium have been obtained, by cultivation and by hybridizing, from the small-petaled Pelargonium of the Cape. Fruits and culinary vegetables are sometimes improved by hybridity. These hybrids cannot be continued from seed. They must be propagated by offsets or cuttings. The effect of hybridizing or crossing is very marked in the case of certain Cereal plants.

This subject has important bearings on the origin and limitation of species. If, as some old authors supposed, there were only a few species originally formed, and all the rest are the result of hybridization, there would be no limit to the production of species, and no permanence in their characters. This opinion, however, is not supported by facts. It is believed that the types of all the species now on the globe were originally placed on it, and have given origin to offspring like themselves, capable of reproducing the species. We have already mentioned that hybrids are rare in a wild state, and they are seldom permanent and fertile, and they have always a tendency to revert to one of the original types.

III.—PHYSIOLOGY OF THE FRUIT.

While the object of fecundation is to develop the embryo in the seed, it causes at the same time changes in the pistil. The stigma and style become dry, and either fall off, as in the Peach, Orange, and Nut, or are persistent, as in the Poppy (Fig. 309), Mangosteen, Clematis, and in many pods. (Fig. 314). The pericarp in some instances becomes swollen, even although the ovule is not fecundated. In such cases the fruit is abortive in as far as reproduction is concerned, although it may be valued for domestic purposes. Many of the best Oranges and Grapes contain no perfect seeds, and the fruit of the Banana, Plantain, Bread-fruit, and Pine-apple, is most palatable when it is seedless. The age of trees seems to have an influence over the production of seeds. In the case of the Orange, it is said by Bullar that old trees often produce seedless fruit.

The fruit during its growth attracts nourishment from the surrounding parts, and it is of importance that it should receive a large supply of elaborated sap. In their natural state some plants exhaust themselves in the production of fruit, and die after one year, if annuals, or after two, if biennials. Sometimes fruiting is long delayed, and ultimately takes place vigorously and abundantly. This is observed in plants such as the American Aloe, which only fruits once after many years, and then dies. The division of plants into Monocarpic (άνοιξ, one, and καρπός, fruit) and Polycarpic (πολύς, many) is founded on their times of flowering and fruiting. The former are such as flower and fruit only once in their life and then die; and this may take place at the end of one year, two years, or many years. The latter are such as flower and fruit many times in the course of their lives. A plant which has been prevented by an inclement season from perfecting its fruit, will often bear a large quantity the following season, if genial. An annual, by being prevented from fruiting, may be made to endure for two or more years. The increased vigour of perennials enables them to withstand the exhaustion induced by fruiting.

In the case of cultivated plants, where the object of the gardener is to have a supply of good fruit, many artificial means have been adopted to promote the development and maturation of the pericarp. The application of manure to the soil, by increasing the vigour of the plants, aids in this matter; also checking the branches by judicious pruning, so as to cause a great flow of sap to the fruit; and cutting a ring of bark from the branches, so as to produce accumulation of sap above the wound. In ringing the bark, care must be taken to make the cut so that the two lips of the wound may reunite in the course of a few months. If the cut is large, then the branch may be destroyed. It is prudent not to ring the bark of the main stem, but only that of branches; and the wound should be covered with grafting-clay and damp moss, so as to allow the healing process to go on. Checking the roots has an important influence on the production of fruit. When fruit sets in large quantity, it is prudent to thin it early, and thus allow only a moderate quantity to come to perfection. As the sap is distributed to the whole fruit, this operation will permit more nourishment to go to that which remains. By judicious thinning, although the quantity of fruit is diminished, its quality is much improved.

The pericarp sometimes preserves its green colour and leafy aspect, as in the Pea, and continues to act as leaves do, decomposing carbonic acid during daylight, and giving out oxygen. Sometimes the cells of the pericarp become hardened and thickened by the deposit of lignine, and the seed-vessel becomes dry, assuming a white or brown colour. In these circumstances its vital functions cease, and it no longer produces any marked effect on the air. In other instances the pericarpial cells contain matters which, in the progress of maturation, undergo chemical changes, so that the fruit becomes succulent, and its epicarp assumes various tints of red, yellow, and blue. As transpiration and evaporation take place from the surface of succulent fruits, the fluids in the outer cells become thickened, and thus promote the endosmotic action between them and the cells containing thinner liquids. In this way the fruit swells considerably. When the fruit has attained its full size the stalk dries up, and may be easily detached from the plant; at the same time waxy matter is deposited in the cuticle, which prevents the drying process from going on rapidly.

During their early state pulpy fruits are tasteless or slightly bitter, and they have at that time the structure and chemical constitution of leaves. In their second stage of development they acquire a sour taste from the production of acids, such as malic acid in the Apple and Gooseberry, tartaric acid in the Grape and Tamarind, citric acid in the Lemon, Orange, Red Currant, and Cranberry. In the third stage, or that of ripening, the acids diminish in quantity, they are more fully neutralized by the alkalies present in the fruit, and are partially decomposed; the cellulose forming the walls of the cells and vessels is also transformed, and along with the gum is converted into grape sugar. Saccharine matter may be formed from the acids in the fruit, by the addition of the elements of water, and the separation of oxygen. The changes which take place during ripening consist chiefly in a diminution of the quantity of water and of ligneous matter, and an increase in the quantity of sugar. Saussure and Couvercelle state that ripe Grapes, Apples, and Pears, when separated from their respective plants, and kept at a temperature of about 60° Fahr., gave out carbonic acid.

Berard thinks that these changes in fruits depend essentially on the action of the oxygen of the air. Fleshy fruits, he says, may be preserved with little alteration for many weeks in vacuo, in nitrogen, and in hydrogen gas; Peaches, Plums, and Apricots, may be kept from twenty to thirty days, and Pears and Apples for three months, in a sealed bottle, containing a little sulphate of iron, lime, and water, which remove the oxygen of the air. Fremy found that the ripening of the fruit was arrested by covering it with varnish, which he supposes to act partly by preventing the access of air, and partly by stopping the transpiration, and thus checking the flow of sap into the fruit. Couvercelle says that the sugar of fruits is formed by the action of organic acids on the gum, dextrin, and starch; while others think that the cellulose and lignine are also transformed into sugar by the action of acids.

Certain fruits, more especially those belonging to the natural orders Pomaceae and Ebenaceae, after being ripe, undergo a series of chemical changes when pulled and allowed to remain in a room at a moderate temperature. The austerity of Medlars is diminished under this process, to which the name of blettting (French, blette) is given by Lindley. It is a stage intervening between what is commonly called ripeness and decay. The chemical changes consist in a loss of weight, in consequence of a separation of water and a diminution in the quantity of saccharine and ligneous matter. There is a slight increase at the same time in the albuminous matter and in the malic acid. During the maturation of certain fruits, oily and aromatic substances are produced which give a peculiar flavour. In fruits which form jellies, there is developed a gelatinous matter, to which the name of Pectic acid is given.

The greater number of plants ripen their fruit considerably within a year from the time when the flower expands, and some require only a few days for the purpose. Some trees, as certain species of Oak, require eighteen months; Juniper fruit, and cones of the Firs, the fruit of some American Oaks, and of the Metrosideros of New Holland, hang above twelve months; and the Cedar requires twenty-seven months to mature its fruit or to bring its seeds to perfection. The Orange presents a singular phenomenon in respect to maturation of its fruit. This is generally looked upon as ripe at the end of the first year; but it often happens in the south of Europe that, in order to obtain Oranges of the best quality, the fruit is allowed to remain for a second summer on the tree. It is not easy then to say what is the real term of maturation in this fruit in its natural state. Discussions have arisen as to the time when the fruit of the cereal plants is most productive to the farmer. Many think that wheat ought to be cut before the fruit reaches perfect maturity, inasmuch as it then yields most flour. When allowed to remain till fully ripe, then the outer covering or bran thickens at the expense of the flour. Such is also said to be the case in Oats. About a fortnight before ripening is said to be the proper time for cutting corn, as the skin is then thinner, the grain fuller, the bushel heavier, and the yield of flour greater.

The period in which fruits ripen is materially accelerated by an increase of temperature, and their flavour is also improved. Hence the use of putting fruit under glass, or on slates of a dark colour, or wrapping it up in thin bags. The maturation is also accelerated by removing a ring of bark from the branch or stem, which leads to an accumulation of descending sap above the cut. When fruit trees belonging to a cold climate are transferred to a hot one, it frequently happens that no fruit is produced; the leaves become luxuriant, and the flowers, if they expand, are abortive. A high temperature sometimes seems to cause the production of unisexual male flowers only. Hence plants in hothouses when over stimulated by continued heat, are often abortive. They require a season of rest or repose in order to perform their functions properly.

IV.—PHYSIOLOGY OF THE SEED.

1. Maturation of the Seed, and Modes in which Seeds are scattered and deposited in the Soil.

The production of an embryo is the object of fertilization. In the case of flowering plants this embryo is contained in the seed, in which it attains a certain degree of development. In these plants after impregnation the ovule undergoes evident changes. The embryo plant enlarges, attracts nourishment from the surrounding tissues, and either absorbs all the contents of the ovule, or becomes surrounded by a store of perisperm (albumen) which is deposited within or on the outside of the embryo-sac, or in both situations. The nucleus of the ovule is either absorbed or becomes filled with various azotized and unazotized matters, while the coats (especially the outer one) become denser and firmer, and the foramen is closed. Lignine is often deposited on the walls of the cells of the episperm. The seed by means of these changes is rendered more fit to resist vicissitudes of temperature and other accidents which might injure the vitality of the embryo.

An aperispermic embryo (Fig. 334) has all the nutriment contained in its own substance, especially in its cotyledons, and when the coats of the seed are removed the embryo alone is found within. A perispermic embryo has a separate store of nutriment beside it, and when the seed-coats are taken off the embryo is found surrounded more or less completely by this nutritive matter or perisperm (Fig. 335). The perisperm consists of amylaceous, gummy, and saccharine matters, with oils, resins, nitrogenous substances, and certain salts, such as phosphates, sulphates, and chlorides. The presence or absence of perisperm seems to be connected with the mode in which the seed germinates, and the nature of the perisperm varies according as the seeds sprout rapidly or lie long dormant in the soil. The store of nourishment laid up in the seed is greater than the embryo requires in ordinary circumstances. When the perisperm is not allowed to be fully formed before the seed is detached from the plant, it sometimes happens that owing to the soft and succulent condition of the albumen, the embryo sprouts rapidly. In such cases, however, the embryo does not germinate vigorously, and is apt to fail from want of a due supply of nutriment. Some seeds continue to be of a soft texture, while others assume a stony hardness, as is the case in the Date, and in the Ivory Palm. Some ripe seeds are of greater specific gravity than water, and sink when thrown on it. In other instances, especially when air is contained in the envelopes, as in the Indian Cress, the seeds float in water.

When the seed is ripe, it is either discharged from the seed-vessel, or the fruit remains indehiscent, and falls with the seed still contained in it. Fleshy fruits, such as Apples and Peaches, fall from the tree when ripe, and their succulent portion serves as nutriment for the young embryo while sprouting. Many dry fruits, especially such as are monospermal, (Fig. 317) fall along with the seed which they inclose. In the cereal grains the pericarpial covering and the integument of the seeds are incorporated, and in the fruit of Labiateae and Boraginaceae these two coverings continue attached when the seed is ripe. In Composite (Fig. 206) and Valerian the hairy calyx remains attached to the fruit, so as to be the means of dispersing it along with the contained seed, and in samaroid fruits (Fig. 322) there are winged appendages for the same purpose. In the case of the Dandelion (Fig. 155), the receptacle, which is at first succulent and flattened, becomes dry and convex, and the phyllaries, which are erect, become deflexed, so as to allow the fruit to be easily scattered. Other dry fruits dehisc in various ways, as already mentioned, so as to scatter the seeds. The opening of the seed-vessels takes place either as the result of a drying process, as in Mahogany, or from the effects of moisture, as in species of Mesembryanthemum, and in the pod of Anastatica hierochuntina, commonly called the Rose of Jericho. Some plants are called Hypocarpogen (κάρα, under, καρπός, fruit, and γῆ, earth), because their fruit is subterranean—that is, it is either produced on peduncles underground, or, after being ripened in the air, is pushed into the soil by a curvature of the fruit-stalk. Vicia ampliflora and Lathyrus setifolius ear. ampliflorus produce fruit both on aerial and subterranean branches. Arachis hypogaea, called Earth-nut, produces on its aerial branches abortive flowers, while on those underground it develops perfect pods. The peduncle of Linaria Cymbalaria at the time of flowering is straight and short, but it afterwards elongates and curves irregularly, until it comes to a fissure in the rock or wall on which it grows; there it inserts the capsule, which subsequently allows the seeds to escape. The extremity of the peduncle of Trifolium subterraneum is provided with a hard point, by means of which, after its curva- tion, it penetrates the soil and deposits its pods.

Seeds are sometimes provided with hairy and winged appendages, as seen in the case of Cotton, Willow, Asclepias (Fig. 329), Pine (Fig. 328), Mahogany, and Bignonia, for the purpose of being wafted to a distance by the agency of winds. The seeds of plants valuable as food have been dispersed by man over various quarters of the globe. Streams also convey to a distance the seeds of plants which grow on their banks. The pulpy covering of some fruits renders them fit for the food of birds and other animals, and when the seeds are hard and inclosed in a stony endocarp, they may escape the action of the gastric juice, and be deposited in a state fit for germination. Seeds are scattered in such a way as to reach the soil best fitted for their growth, whether the plants are terrestrial or aquatic.

2. Germination.

Germination (Germinatio, springing), is the term applied to the sprouting of the embryo when placed in circumstances favourable for its growth. In the case of flowerless plants a cell or spore separated from the parent plant is developed into a new organism, while in flowering plants an embryo plant already in a certain stage of development within the seed, begins to send out first its root, and then its cotyledons and primary stem-bud. In the case of the latter class of plants, germination may be defined the act by which the fecundated embryo of a seed leaves the state of torpor in which it has remained for a longer or shorter period, starts into life, as it were, comes out from its envelope, and sustains its existence until such time as the nutritive organs are developed.

Requisites for Germination.—In order that germination may go on, certain conditions are necessary. The most important of these requisites are moisture, a certain temperature, and air. The absence of light is also favourable for the process, and, according to some, electricity promotes it. In general, seeds do not sprout until they are placed in the position which the plants are subsequently to occupy. Occasionally, however, seeds begin to germinate before being detached from the plant, as in the case of the Mangrove tree.

A certain amount of moisture is required for germination. If seeds are kept in a dry state they can be preserved for a long time without sprouting. Water is required for the solution of the nutritive matter of the seed, as well as for exciting the endosomatic action of the cells. No circulation nor movement of fluids can take place in the seed until water is taken up. The nourishment of plants is absorbed chiefly in a liquid state. Seeds imbibe a large quantity of water, and in so doing their cells become much distended. By this means they are enabled to burst the hard endocarpal coverings which often surround them, as in the case of what is called stone-fruit.

The amount of heat required for the development of the embryo varies much. Some seeds, as those of plants belonging to cold regions, require a moderate temperature, others belonging to hot countries demand an elevated one. It may be said in general that a temperature varying from 60° to 80° F. is the most favourable for germination. In cold regions the spores of Cryptogams germinate at a very low temperature. In other instances germination proceeds at high temperatures. Dr Hooker states, that on the edges of hot springs in the valley of Soane in India, the temperature of which was sufficient to boil eggs, there occurred sixteen species of flowering plants; he also mentions Ranunculus sceleratus as growing in the vicinity of hot springs near Monghyr in India, at a temperature of 90°.

The necessity of air for germination was demonstrated by Ray, Boyle, and others, before the chemical composition of the atmosphere was discovered. Scheele, Senebier, and Saussure showed that the presence of oxygen gas was required in order to aid in the changes which take place in the seed. When seeds were placed in an atmosphere of hydrogen, nitrogen, and carbonic acid, they did not germinate. When they are buried deeply in the soil, so as to be deprived of the access of air, they do not grow. In such circumstances, when the soil is turned up so as to bring the seeds near the surface, germination often commences. In this way seeds, which have been long dormant, spring up on the embankments of railways, and white Clover frequently appears when the soil is stirred. Some substances which supply oxygen, as weak solutions of chlorate of potass and of oxalic acid, are said to be useful in promoting germination. Chlorine acts in the same way by decomposing water and setting oxygen free. Seeds germinate more rapidly in shade than in light, and in diffuse daylight more quickly than when exposed to the direct solar rays. Experiments have been made as to the effect of different rays on germination. Senebier found that the plants illuminated by the yellow rays grew most rapidly in height; next those in the violet rays; afterwards those in the red; and he concluded that the height and size of a plant was proportionate to the intensity of the illumination, while its verdure depended more on the quality of the rays.

Hunt made experiments on the effects of coloured rays on the germination and growth of plants by passing the sun's rays through variously coloured glass. He concluded that the processes of germination and budding are essentially influenced by the chemical principle actinism, transmitted through the blue media; and that while the rays connected with blue light promoted germination, the luminous yellow rays impeded it.

While moisture, heat, air, and darkness, are favourable to germination, it is of importance that these requisites should be properly supplied. In nature seeds are sown in the earth to a moderate depth, so as to be excluded from light, and at the same time to be acted on by air; moisture is supplied by rains and dews, and a certain temperature is given. Such is the plan which we ought to imitate in garden and field operations. In order that seeds when scattered may be placed at a proper depth, the soil must be properly ploughed and pulverized. The preparation of the soil materially promotes germination; when properly ploughed the seeds sink to the same depth throughout the field. The advantage of equal machine-sowing is, that the seeds germinate about the same time, and the crop is also all ripened at once, and the diminution in the quantity of flour caused by allowing some part of it to remain long in a ripe state is avoided. When seed is sown broadcast by the farmer, a certain quantity remains uncovered even after harrowing, and hence it does not germinate freely. This may be one reason why dibbling is more successful as regards the number of seeds which germinate, and why with a smaller expenditure of seed an equal return is made.

The experiments made in regard to the depth at which seeds should be placed, agree in showing the advantage of shallow sowing. The more slightly the seed is covered by the earth, the more rapidly the bud makes its appearance, and the stronger afterwards is the stalk. The deeper the seed lies, the longer the shoot remains before it comes to the surface. Ugazi, from observations made in Bavaria, gives half an inch and one inch as being the best depths at which ordinary cereal grains, as well as Peas, Millet, Maize, Buckwheat, and Lentils, should be sown in argillaceous soils, while two to three inches is the depth proposed in sandy soils.

Draining.—In order that land may be productive in the case of cultivated grains, moisture must be supplied in proper quantity, and a certain amount of heat must be imparted to the soil. This is accomplished by the operation of draining, which has been carried to great perfection of late. Much injury is inflicted on the soil by stagnant water. The land is rendered cold, inasmuch as the sun's rays, in place of being expended in heating the soil, are absorbed by the water, the temperature of which is not raised so rapidly as that of the earth or of the air. There is thus a great loss of heat. Drained land in summer is from 10° to 20° warmer than water-logged land. Moreover, by the exclusion of air there is often an imperfect decay of vegetable and animal matters in the soil, so that acids are produced which are deleterious and hurtful to vegetation. The importance of giving bottom heat to plants cannot be too strongly insisted on.

The object of draining is not so much to get rid of the water, as to make it percolate freely through the whole of the soil, laterally as well as perpendicularly, and thus obtain from it the nutriment, in the shape of ammonia, carbonic acid, &c., which it contains. As the water disappears, air occupies its place, and hence drained soil is aerated. The effects of draining are both mechanical and chemical. It gives rise to improved efficiency in ploughing, harrowing, and weeding, besides saving seed. It also aids the fertilizing power of manures, ameliorates the climate, raises the temperature of the soil, accelerates the harvest, and improves the herbage and other crops.

The depth of drains, and their distance from each other, must be regulated by the nature of the soil, and of the subsoil. Drains should of course never be shallower than the known depth to which the roots of annuals descend. By making deep, and at the same time efficient drains, we increase the quantity of soil available for the purposes of plants. In the case of deep-rooted plants, it is essential that water should be removed from the lower as well as from the upper portion of the soil. Drains must be kept clear, otherwise their good effects will be lost. Occasionally they become choked up, the roots of plants getting access to them. All that can be done to prevent this, is to make deep drains, and not to allow them to pass near trees; also to keep the land clean.

Vitality of Seeds.—Some seeds must be sown immediately after they are ripe, otherwise they lose their vitality, and decay. This is the case with the seeds of Magnolia, Coffee, Clove, and with those of an oily and mucilaginous nature. Even though the germinating power is lost, the seeds may be in a state fit for food. The seeds of the double Coco-nut (Lodoicea Seychellorum), when carried from the Seychelles Islands to the Maldives, and those of Entada (Purusetha) scandens, when borne by the Gulf-stream from the Antilles to the outer Hebrides, are to all appearance fresh, although they will not sprout when planted. Seeds with very delicate integuments can seldom be kept longer than a few weeks or months, while hard and bony seeds have been known to germinate after the lapse of many years. Certain seeds are known to retain their germinative powers for a long time. The seeds of Cucumber have germinated after seventeen years, those of Colza and Malva crispa after eighteen, of Althaea rosea after twenty-three, Maize after thirty, Haricots or French beans, after thirty-three, Melons after forty-one. For sixty years a bag of seeds supplied the Jardin des Plantes annually with sensitive plants. Haricots taken from the Herbarium of Tournefort, and which were at least one hundred years old, were found to germinate, as were also seeds of Hieracium, fifty years old, from Fries' Herbarium. Grains of Rye have been found fertile after one hundred and forty years.

Seeds placed in particular circumstances have retained their vitality for a great number of years, and even for centuries. Savii saw for ten years young Tobacco plants continue to spring up in his garden from seed which had been sown naturally. All the young plants were regularly rooted out, and yet the supply continued for the length of time mentioned; showing that many seeds remained dormant, and only appeared as the soil was turned up and exposed to air. Dalhamel noticed the re-appearance of Datura Stramonium, after twenty-five years, in a ditch which had been filled up and afterwards cleared. Miller noticed Plantago Psyllium grow in a ditch at Chelsea which had been newly cleared, and where it had never been known to grow in the memory of man. Lindley mentions the germination of Raspberry seeds found in 1834 or 1835 in an ancient barrow (tumulus) near Maiden Castle, along with coins of the Emperor Hadrian. The seeds were found in a coffin thirty feet below the surface, and may have been 1600 to 1700 years old. In Stirlingshire germinative seeds of the Corn Marigold (Chrysanthemum segetum) were found under six or seven feet of peat moss. When new land is turned up it frequently happens that seeds spring up which have lain long dormant. White Clover (Trifolium repens) appears in these circumstances. Fumaria micrantha has been known to appear in large quantity on newly stirred ground near Edinburgh. After extensive conflagrations plants often make their appearance which had not been previously seen in the neighbourhood.

It is not easy to account for the manner in which the vitality of many seeds is thus preserved. Uniform temperature, moderate dryness, and exclusion from light and oxygen, appear to be essential requisites. If the temperature is elevated, and moisture and oxygen are present, then germination commences. The vitality of seeds in certain favourable circumstances may thus be preserved for a very extended period, but it is by no means easy to imitate these conditions. The statements made in regard to the preservation of Mummy Wheat have not been confirmed by careful observation. Even in the cases which appeared to be conclusive, fallacies have been detected. Thus Mummy Wheat, supplied by Sir G. Wilkinson to various parties, was found in some cases to contain grains of Maize, a plant of the New World, which leads to the conclusion that in this case the grains had been tampered with. We have no evidence that the Wheat now cultivated as Mummy Wheat was that deposited 3000 years ago in the mummy cases.

Preservation of seeds in a germinating condition is a matter of importance in as far as the introduction of plants from abroad is concerned. Seeds brought from India to Britain round the Cape rarely vegetate freely, while those brought overland succeed well. Seeds are best transported in their pericarps. The flinty coatings of many foreign legumes will preserve the living germ for an indefinite period. In preserving seeds an important requisite is to have them ripe and dry. Such seeds should be put into dry paper, and exposed during transportation to free ventilation in a cool place, as for instance in a coarse bag suspended to a nail in a cabin. Many seeds which cannot be transported when exposed to air, will retain their vital properties if buried in clay. Oily seeds, and those having much tannin in their composition, as Beech-Mast, Acorns, and Nuts, must not only be ripe and dry, but also must be excluded from the air. They are usually put into dry earth or sand pressed hard; or they are preserved in charcoal powder, and enveloped in tin or wax. Exalbuminous seeds, and those having dense and fleshy albumen, bear transportation best. Mr McNab has suggested a mode of transmitting seeds by having a strong box about ten inches square, with the sides three quarters of an inch thick, in which alternate layers of earth and seeds are placed, the whole being firmly pressed together. On the arrival of such a box the layers of earth and seeds are taken out in succession and put into separate boxes. Wardian Cases may also be employed for the transmission of seeds in earth. The seeds will thus be brought frequently in a germinating condition.

Alphonse De Candolle finding that there have been fallacies in regard to the vitality of seeds, from not attending to the particular circumstances in which they have been preserved, made experiments on the subject by taking seeds of different natural orders, collected simultaneously in the same garden, transported and preserved in the same manner, sown in equal numbers, and in similar conditions of soil, humidity, and temperature. The seeds were collected in the Florence Garden in 1831, and were sown on the 14th May 1846, being nearly 15 years old. He selected 368 species belonging to about 150 different genera, and 53 families. Twenty seeds of each were sown in peat mould in pots, and watered. The pots were kept under examination till autumn. The mean temperature in June, the period when several species sprang up, was 60°2° F., that of July 65°3° F., and the maximum reached 86° and 87°8° F. Out of the 368 species only 17 germinated; of the 17 species which came up, Dolichos unguiculatus was the only one that yielded more than one-half the seeds sown, viz., 15 out of 20; others had 1, 2, or 3 germinations in 20 seeds. Lavatera cretica approached nearest Dolichos, but there were only 6 out of 20 that germinated. Woody species seem to preserve the power of germinating longer than others, whilst biennials are at the opposite extreme. Perennials probably lose the power of germination more quickly than annuals. Large seeds appeared to De Candolle to preserve the power of germinating longer than small ones. The presence or absence of separate albumen did not seem to make any difference. Some albumens, such as those of Coffee and of Umbelliferae, are difficult to preserve from special chemical conditions. Compositae seem to lose their germinating power very early. From other experiments, De Candolle concludes, that the duration of the faculty of germination is frequently in an inverse proportion to the power of germinating quickly.

Time required for Germination.—The time required for the germination of seeds depends greatly on the texture of their coats, as well as their age. Some exalbuminous seeds, such as Cresses, which are also very hygroscopic, sprout in twenty-four hours, others require many days, or even months. Hard seeds, such as those of some Palms, lie long dormant. Large seeds are slower in germinating than small ones, because they require more water, and their absorbing surface does not increase in proportion to their size. Seeds having an osseous or stony spermoderm, and those which are sown naturally while contained in a hard pericarp, as nuts and acorns, germinate more slowly than others. The germination may be expedited by thinning or chipping the envelope, so as to allow water to penetrate more easily. Many of the seeds inclosed in a hard shell or stone germinate in the midst of a decaying mass, which must contribute to the decomposition of the shell. Soaking hard seeds in water, or causing them to pass through the digestive canal of animals, greatly accelerates germination. The seeds of Hawthorn, and others of a similar nature, are thus often deposited by birds in peculiar localities in a state fit for immediate germination.

Alphonse De Candolle examined the germination of seeds in the open air and in a stove, and the following table shows the general results:

| NAMES OF SPECIES | NUMBER OF DAYS REQUIRED FOR GERMINATION | |-----------------|----------------------------------------| | | In the open air, 60°4° to 65°6° F. | In a stove, 64°9° to 77° F. | | Erigeron canadensis | 10 | 2 | | Thlaspi ceratocearpum | 8 | 4 | | Dolichos abysinicus | 10 | 3 | | Zinnia tenellula | 11 | 5 | | coccinea | 22 | 5 | | Grahamia aromatica | 14 | 5 | | Sida daga hirta | 11 | 5 | | Lathyrus vulgare | 14 | 10 | | Anthocephala rigescens | 7 | 6 | | Rheum undulatum | 8 | 7 | | Duvana dependens | 22 | 16 |

The rapidity with which some annuals germinate in arctic regions when the heat of summer returns is very remarkable. They pass through their periods of germination, flowering, and fruiting in a very short period. Such is also the case in warm countries after the dry season. After the dry season in the Brazilian plains, and when the first few showers have fallen, Gardner remarked that the annual Grasses pushed forth their blades with astonishing rapidity and vigour. Spruce states that on the sandy shores of the Amazon and Tapajoz, after the waters leave them, several small annual or rather ephemeral plants spring up. They start up from the sand, flower, and ripen their seeds in the course of a few days, and then wither. Amongst them are Chemical changes during Germination.—During the germination of seeds, alterations take place in the nature of their contents. When the embryo occupies the entire seed, changes occur in the cotyledons, by means of which nutritive matter is prepared; when there is a separate store of perisperm, its constituents are acted upon by moisture, heat, and air, so as to undergo chemical changes. Alterations take place in the azotized matter, and part of the fibrin gives origin to diastase, which acts as a ferment; acetic acid is also formed, and the starchy matter is converted into dextrin and grape-sugar. Thus insoluble matters are rendered soluble, and a large amount of saccharine matter is produced. At the same time there is an evolution of carbonic acid, in consequence of a combination between the oxygen of the air and the carbon of the seed, and as the result of this chemical action a certain amount of heat is developed. The heat is carried off very rapidly by the soil in ordinary cases, so that it is difficult to ascertain its amount; but when seeds are laid in moist heaps the increase of temperature becomes apparent.

In the malting of Barley these changes are well seen. The grain is steeped in water in the first instance, so as to soften and swell; it is then laid in heaps 30 inches deep for 20 or 30 hours. In this situation it becomes warm, and germination commences. This is moderated by laying the grain in thin strata of a few inches thick, on large airy but shaded floors. There it remains 12 or 14 days, until germination is sufficiently advanced, being frequently turned in the meantime, in order to allow each grain to germinate equally, and to prevent entangling of the radicles of contiguous grains. During this process sugar is formed, which is intended for the nourishment of the young plants, and if left long it would all be absorbed. This is prevented and germination stopped by exposing the grain in a kiln to a temperature rising from 100° to 160° or more. Thus the grain is dried and its vitality destroyed.

During germination it is probable that there is a certain electric disturbance. Carpenter says, the conversion of the starch of the seed into sugar involves the liberation of carbonic acid, and of a small quantity of acetic acid. Now as all acids are negative, and as like electricities repel each other, it is probable that the seed is at that time in an electro-negative condition. Hence germination is said to be quickened by connecting the seed with the negative pole of a feeble galvanic apparatus, whilst it is retarded by being connected with the positive pole.

Acotyledonous germination.—When the spores of the lower Acotyledonous plants germinate, they send out cellular processes of a more or less conical form, which serve the purpose of roots, and which often divide. These cellular prolongations may be formed from the entire walls of the spore, or from its inner covering. In Figure 413 are seen the germinating spores of a species of Liverwort (Marchantia), in which there is a protrusion of root-like processes. When these tubular prolongations protrude through the outer coat of a spore, they exactly resemble the pollen tube, which may be considered as the result of the germination of a single cell placed on the stigmatic surface—the soil fitted for its growth (Fig. 388). In Figure 414, the spore of a Seaweed (Fucus cirratus) is represented during germination, with its cellular roots protruded through the epispore. In these germinating spores one part appears as a root-like portion, while the opposite end is developed as a thallus bearing fructification.

In the case of Fungi, there is produced a peculiar subterranean axis called mycelium or spawn, on which the fructification is ultimately developed (Fig. 369 a). This mycelium spreads equally on all sides from the original point of development. In this respect it is analogous to the thallus of Lichens. In the case of many Agarics numerous pilei arise from the outer part of the mycelium in the form of a circle, and thus a fairy ring is formed; in the same way as in many Lichens the thallus spreads in a circle, and at its extremities produces fructification or apothecia. A large fairy ring, formed apparently from many individuals of one species of Fungus disposed in a circle, really constitutes the organs of fructification of a single individual only.

The spores of many of the lower Acotyledons, such as Fungi, are so minute as to be easily scattered by the wind, and thus they are sometimes developed in very anomalous situations. Spores sometimes find a nidus in diseased structures in man and animals. Thus, in the disease of the skin called Porrigo favosa, as well as in Mentagra and Aplathia, peculiar cellular bodies are produced, which appear to be altered and metamorphosed vegetable forms. In the case of the Silkworm, a Cryptogam called Botrytis Bassiana is found in a disease to which they are liable, and which has been called Muscardine. Caterpillars exhibit occasionally germinating spores of species of Sphaira. Sphaira Robertsii grows on the larva of Hepialus virescens in New Zealand. Other Sphaerias are produced in similar situations. Species of Polistes are seen flying about in the West Indies with vegetable growths projecting from them. They are called vegetating wasps. Leida finds numerous fungal forms infesting the intestines of different species of Iulus, and also attacking the Entozoa in the intestinal tube of the animal. The spores of Fungi are diffused in the air, ready to alight on any body which can furnish a nidus for them. In this way various kinds of Mould are developed—the spawn or mycelium produced from the spore ramifying through the decaying matter, and sending up at intervals fructification. In some cases the mycelium becomes remarkably developed, and does not produce ordinary spore-bearing organs. Thus in vinegar and syrup a fungoid mass is often produced, which is probably a modified form of some kind of Mould. The Vinegar-plant seems to be a peculiar mycelial development of the Mould called Penicillium glaucum. During the germination of the spores, certain changes are induced in the fluid surrounding them. Thus a saccharine solution is converted into vinegar. The mycelium is sometimes formed in separate layers, which can be detached from each other, so as to form independent vegetating masses. The spores of a Fungus (Merulius lachrymans), when introduced into wood, germinate, and produce the disease called dry-rot.

In higher Cryptogams the spore produces first a cellular prothallus, whence roots and reproductive organs proceed. In Mosses the germinating spore forms, in the first instance, a cellular prolongation, which becomes a conferva-like germ, whence buds arise, bearing the leafy plant with its fructification. This is shown in Figure 415, where a germinating spore, a, of a Moss is seen protruding a cellular process, which elongates and divides, as seen at b, and finally, as shown in Figure 416, forms a jointed cellular prothallus, p, whence buds are produced, a, b, bearing the leaves and the organs of reproduction. In Ferns the spore gives origin to a thallid expansion, the prothallus, whence roots proceed, and ultimately the sporangiferous frond. In a monocotyledonous seed there is generally a supply of albumen, which is gradually dissolved and absorbed as germination proceeds. Sometimes the whole of the perisperm and its cells disappear; at other times, as in the seed of the Ivory Palm (Phytelephas macrocarpa), a portion is removed, and a sort of cellular skeleton is left within the seed. The radicular portion of the axis is more or less truncated, and sends off numerous rootlets, which pass through sheaths or coleorhizae formed by the lower part of the axis. This is shown in the germinating grain of Wheat (Fig. 419), in which the rootlets, \( r \), are covered with cellular hairs for the purpose of absorption. The central root is first developed, and the others come off in succession as secondary rootlets. When there is no albumen present, the cotyledon is usually pushed upwards beyond the seed.

In many perispermic monocotyledonous seeds the cotyledon is partly contained within the seed, and partly appears externally. That portion within the seed is called intraseminal, and corresponds to the blade or lamina of the leaf; the narrow protruded portion, which varies much in length, represents the petiolar portion, which often ends in a sort of sheath embracing the axis. In Figure 420, a representation is given of the seed of the Indian Shot in different stages of germination. A portion, \( c \), of the single cotyledon remains within the seed, while another portion, \( d \), protrudes, ending in a sheathing portion, \( s \), which surrounds an axis, \( t \), whence spring the radicles, \( r r' \), which pass through sheaths, \( c o l \), and a primary bud, \( b \), which rises to form the stem. A similar development is observed in the Coco-nut.

In Grasses, as shown in Figure 63, the cotyledon, \( c \), enlarges within the seed, and, on one side of the perisperm, roots, \( r \), are protruded through sheaths, \( c o \), while the plumule, \( g \), rises upwards, consisting of sheathing leaves arranged alternately. The sheathing cotyledon, \( c \), with the radicle and the plumule, are also represented in the Maize or Indian Corn, in Figure 60. In all cases of monocotyledonous germination, after the radicles have descended into the soil, the plumule or first bud of the axis is developed, and the leafy stem is gradually formed. The leaves are usually alternate, and are often sheathing.

Dicotyledonous germination.—In dicotyledonous germination the radicle is protruded through the foramen of the seed, and then the cotyledons are either protruded, so as to appear above ground as epigeal leaves of a green colour, or they remain within the covering of the seed as fleshy hypogeal lobes, containing much nutriment in their substance. The first kind of germination is seen in Figure 421, where the embryo of a Sycamore is depicted with its radicular axis, \( r \), giving origin to roots, its ascending axis, Botany. a, with the two cotyledons, c.e, which are green, leafy, and epigean, inclosing the first bud, b. The second kind of dicotyledonous embryo may be illustrated by the Bean and Pea (Fig. 61), where the fleshy lobes, c.e, which form the great bulk of the seed, are hypogean, and are gradually absorbed during the growth of the plant.

The dicotyledonous seed is sometimes exalbuminous or apispermic, as in the Pea (Fig. 61), in which the fleshy cotyledons have a store of nutriment laid up in them for the growth of the embryo; at other times the seed is albuminous or perspermic, as in the Pansy (Fig. 335), and then the nutriment is separate from the embryo, and is gradually dissolved and absorbed during germination. Sometimes the two cotyledons become united, and when the embryo germinates they appear as one; at other times divisions take place, so that the embryo becomes polycotyledonous, as in Firs (Fig. 841). After the cotyledons have appeared they separate so as to allow the first bud, called plumule or gemmule, to be developed between them (Fig. 421, b). This bud forms the axis on which the leaves and flowers are produced. In proportion as the permanent leaves increase, the cotyledonary leaves (after acting as temporary organs of nutrition) wither and fall off, and if they are subterranean they are gradually absorbed. The leaves which are produced in succession sometimes differ in their form. Thus in Victoria regia the youngest leaf is linear and almost filiform, the next is hastate, the third sagittate, and the fourth is nearly ovate, with a deep incision at the base. The future leaves gradually assume a more or less circular form, generally with a distinct line showing the place of the union of the lobes. The rate at which the axis increases varies according to the amount of temperature and moisture which is supplied.

CHAPTER IV.

SOME GENERAL PHYSIOLOGICAL PHENOMENA CONNECTED WITH VEGETATION.

I.—PROPAGATION OF PLANTS BY BUDS AND SLIPS.

Besides the propagation by means of seeds containing an embryo, or by cellular spores, plants are also capable of extension by division. In unicellular plants, and others of the lowest class, it is common to find each cell possessing the power of producing a new individual, either by simple division or by the formation of a cellular bud. In higher plants this mode of propagation is carried out by means of an assemblage of cells, which are developed into an organ or bud of a more complicated nature, before it is detached. Multiplication by division of cells is very common among the lowest Algae, such as Desmidiaceae and Diatomaceae (Fig. 18). In the case of Lichens the thallus produces gonidia (Fig. 365, g), which appear to be a collection of cellular buds capable of producing independent individuals. On the thallus of Liverworts (Marchantia) cup-like bodies (Fig. 362, g), are produced containing gemmae. In Mosses the power of reproduction by gemmae is very marked.

The higher classes of plants may be considered as consisting of numerous buds united on a common axis. These possess a certain amount of independent vitality, and they may be separated from the parent stem in such a way as to give origin to new individuals. In some instances buds are produced which are detached spontaneously at a certain period of a plant's life. The bulbils or bulblets of Lilium bulbiferum (Fig. 75), and the cloves formed in the axils of the scales of bulbs are gemmae or buds which can be detached so as to form new plants. Such is also the case with corms, as in Colchicum (Fig. 74). In these instances the buds are developed in the usual way in the axils of leaves or scales, that is to say, at the points where they join the stem. Some leaves naturally produce buds on their surface, as may be observed in Malaxis, Aspidium bulbiferum, and Nymphaea micrantha. Other leaves, when placed in particular circumstances, give rise to leaf-buds at their margin. Thus the leaves of Bryophyllum calycinum, when placed on the surface of damp soil, exhibit little shoots all around their edge (Fig. 141). The leaves of Dionaea muscipula can also be made to produce buds, and so can those of species of Génera, Gloxinia, and Aechmeas. In some instances plants, in place of producing seeds, bear peculiar bud-like bodies on their floral axis. This occurs in what are called viviparous or proliferous plants, such as Festuca ovina var. vivipara, Aira alpina, A. cespitosa var. vivipara, Poa alpina, Cynosurus cristatus, Polygonum viviparum, and in some species of Allium. In these viviparous plant (which are often alpine) alterations take place in different parts of the flower by which young plants are produced.

Besides this natural mode of propagation by gemmae, new plants are also produced by divisions of the stem and branches. Many of the lower class of plants increase by a constant division of their axis or filaments. In the higher plants similar modes of propagation occur. Thus the potato is naturally reproduced by means of tubers which are shortened under-ground branches, and sections of tubers containing buds (eyes) produce separate plants. When some underground stems are cut to pieces every fragment is capable of giving origin to buds and new plants. This may be seen in many Carices growing in sand, in creeping grasses, and in the Horse-radish. Hence the difficulty of eradicating these plants. By means of slips or cuttings of the stem, gardeners propagate plants, more especially important varieties. These slips may be at once put into the soil, as in the case of Willows and Cactuses, and be made to put forth roots, or to strike, as it is called. By cuttings gardeners propagate Gooseberries, Currants, Figs, Vines, and some other plants. In deciduous trees the operation is best performed in winter. Sometimes gardeners employ layering, by bending down a branch into the earth, keeping it there with pegs, allowing it to form roots, and then cutting it off from the parent stem. In order to cause layers to form roots, they sometimes make a slit or notch on the shoot, or put a ligature round it, or ring the bark. In striking cuttings of plants, it is of great importance to attend to heat, light, and moisture, and to supply them in proper proportion.

Grafting.—Another mode of propagating plants is by grafting, or by taking a part of one plant and making it grow upon another plant. This process sometimes takes place naturally. The branches of trees, when they come into contact, especially when there is an abrasion of the bark, unite. The subject of grafting has received particular attention from Thouin and D'Albret, and it is fully discussed in the article Horticulture. By means of this process we propagate many woody, resinous, soft, or herbaceous plants, which either supply seeds rarely, or are difficult to strike. from cuttings or layers; and we perpetuate certain varieties, valued either for their fruit, the structure and form of flower, their colour, perfume, the nature of their wood, their general aspect, or the shades and variation of their foliage.

There are certain important requisites which must be attended to in grafting. In the case of Dicotyledonous trees, care must be taken to bring the growing parts into contact—the two albumums and the two fibers. The plants on which grafting is practised must be botanically allied, or at all events there must be a similarity in the composition of their sap. Union may take place between plants which, in their natural state, require the same chemical ingredients in the same proportions. This is generally the case with varieties of the same species, more rarely with plants of different species, and least frequently with such as belong to different genera.

Several advantages are derived from the multiplication of vegetables by grafts. We are enabled to perpetuate remarkable varieties which could not be produced by seed; we procure quickly many valuable trees, which are with difficulty multiplied by other means; we hasten the period of fruit-bearing; and we improve and propagate varieties of fruit trees. In the case of cultivated Apples and Pears, the seeds of our best fruits, such as the Ribston Pippin, the Nonpareil, and the Jargonelle, if sown, will not produce plants bearing these varieties of fruit, but they will have a tendency to reproduce the original species, viz., the Crab-apple or Pear. By means of grafting we are enabled to continue esteemed varieties, and at the same time to impart vigour to young slips by putting them on good and well-grown stocks.

The seeds of certain plants have a tendency to sport, as it is called, especially when highly cultivated and supplied with abundance of good nutriment. This is the case with the seed of the Crab-fruit when sown in good soil. By the art of the gardener an improvement is produced in fruit naturally sour and inedible. The seeds of such fruits, especially after a long period of cultivation, have a tendency to produce plants which bear fruit of a better quality than the Crab. Plants showing such a tendency are carefully preserved, and slips are taken from them and grafted on well grown stocks, and thus additional vigour is imparted. Grafting has the effect of supplying to the scion a store of nutriment ready prepared and at once fitted for use. Moreover, the nature of the stock imparts often certain qualities to the fruit borne by the graft.

Mr Knight entertained the idea that the only true mode of continuing plants was by seed, and that a young shoot taken from an old tree could not be made to live longer than the natural term of life of the tree from which it was taken. On this principle he accounted for the disappearance, or at least the scarcity, of many well-known fruits, such as the Red Streak, the Golden Pippin, and the Golden Harvey. According to Mr Knight's theory, the vegetable individual is a plant which has originated from the development of a single seed; this individual may consist of many detached portions, each of which may exist apart from the others. A cutting of a tree is a part of the individual from which it was taken, and although it may have become a tree, still, according to Knight's view, it is no more than a developed state of a portion of the original plant. All parts of a tree are viewed as having a common end of their life, and different trees raised from one and the same tree by grafts are considered as decaying about the same time as the parent plant.

These views have not been confirmed by the observations of physiologists. Experiments show that young shoots of old trees, when used as grafts or slips, furnish as vigorous plants as the shoots of young trees. A whole series of cultivated plants, such as the Vine, the Hop, the Italian Poplar, and the Weeping Willow, are constantly propagated by division without any decreased power of vegetation being observed. There is no truth in the statement that propagation by seed is the only natural method of reproduction in plants. Many are propagated naturally by stems, bulbs, and tubers. The Sugar-cane propagates by the stem, which, when blown down by a storm, emits roots at every joint; the Tiger-lily propagates by bulbils, the Jerusalem Artichoke and the Potato by tubers, and the species of Achimenes by scaly bodies like tubers. Such modes of propagation do not cause debility, and there is no evidence of plants multiplied by division wearing out. There is however no doubt that cultivated plants become feeble by the influence of various causes, such as exhaustion of the soil, improper food, mutilation, the effects of cold, &c. It is also true that seeds or slips taken from diseased and weak plants will partake often to a certain degree of the constitution of the plants from which they have been taken.

While numerous experiments have proved that the young shoots of old trees, when used as grafts, furnish as vigorous plants as the shoots of young trees, and that Knight's views in regard to there being one common period of death for all parts of a tree, are erroneous, there is still wanting definite information as to the age which trees attain. The duration of their life has not been accurately determined. It exceeds so much the limit of man's life that it is not easy to collect data on the subject. Some exogenous trees attain a very great age. Trees which, in individual cases, attain great ages, belong to the most different natural families. Among them may be mentioned the Baobab, the Dragon-tree, species of Eucalyptus, Taxodium distichum, Pinus Lambertiana, Hymenaea Courbaril, species of Cercalpinia and Bombax, the Mahogany tree, the Banyan, the Tulip-tree, the Oriental Plane, Limes, Oaks, and Yews.

Some maintain that the stock and scion are incapable of producing any influence upon each other respectively, and that each retains to the last its own peculiar quality. This seems to be true, so far as their visible organization is concerned; for when grafted trees are cut down, the timber of the stock and scion remains just what it is in cases where no grafting has taken place, and the shoots that proceed from them generally manifest in like manner exactly their original nature. There can be no doubt, however, that the nature of the stock has a decided effect on the slip or scion, both as regards its nutritive and its reproductive organs. Thus it is stated, that Pears grafted on the Mountain Ash are rendered more hardy, and bear fruit earlier; and when grafted on Quinces they become higher coloured. Apples grafted on the Siberian Bitter-sweet Apple are more highly coloured than when grafted on the Crab. Peaches on Plum stocks are coarser than on Peach stocks. The Beurré-Diel grafted on the Thorn produces hard fruit. This shows that the stock has an influence on the graft, and points out the importance of selecting stocks of good quality. The plan of ennobling fruit trees proceeds on the principle of grafting on superior stocks.

In some instances it appears that the slip or scion has a decided effect on the stock. Thus, according to Hales, if we bud the variegated Jasmine on a non-variegated one, it sometimes happens that the buds sent out from the latter bear variegated leaves. It is reported that at Chelsea the variegated White Jasmine was budded upon a branch of a fine plant of Revolute Jasmine with green leaves, and in the succeeding year a slight appearance of variegation came out on the leaves of the Revolute Jasmine. The next year the branch which had been budded was cut out, so that the Revolute Jasmine was thus apparently deprived of all influence from the variegated bud. Nevertheless, the variegation in the remainder of the plant continued to increase, and the leaves and branches ultimately became all variegated, even more than the White Jasmine, whose bud was originally inserted. Temperature of Plants.—We have already seen that, during the periods of flowering and germination, a considerable amount of heat is evolved. This seems to depend on the combination between the oxygen of the air and the carbon of the plant, and is accompanied with the formation of grape sugar and the evolution of carbonic acid. The heat at these stages of growth is often very evident, more especially in cases where numerous germinating seeds are placed together, and numerous flowers are inclosed in a common covering. The phenomenon requires to be noticed in circumstances in which the heat cannot be carried off rapidly by the air or the soil. It is a matter of interest to determine whether or not heat is produced during the ordinary vital actions going on in the cells and vessels of plants. The investigation of this point has called forth the labours of several physiologists. Hunter instituted a series of experiments respecting the temperature of trees. He bored holes to the depth of ten or twelve inches in the trunks of trees, and inserted thermometers. He found that in spring, autumn, and winter the temperature of the internal part of a tree was usually about two degrees above that of the air. The results, however, were variable, and no satisfactory conclusions were deduced. Schoepf, Bierkander, Maurice, Pictet, and Schubler, made similar experiments, and they agree in giving to trees with thick trunks a temperature lower than that of the air during great heat, and higher than that of the air during extreme cold. In all these experiments the results seem to depend on the effects of the sun's rays, on evaporation, on the temperature of the soil as influencing the ascending sap, and on the bad conducting power of the wood.

While the nutritive processes are going on in the plant there is a certain amount of heat produced. This, however, is speedily carried away by evaporation and other causes, and it is not easily rendered evident. Durochet, by means of Becquerel's thermo-electric needle, showed an evolution of heat in plants. In doing this he required to prevent evaporation by putting the plant in a moist atmosphere. In these circumstances the temperature of the active vegetating parts, the roots, the leaves, and the young shoots, indicated a temperature above the air of $\frac{1}{2}$ to $\frac{3}{4}$ of a degree Fahrenheit. Van Beek and Bergsma, in their experiments on Hyacinthus orientalis and Entelea arborescens, found the proper heat of the active parts of plants about $18^\circ$ F. above that of the air. The vital or proper heat of plants, according to Durochet, is found chiefly in the green parts, and it undergoes a quotidian paroxysm, reaching the maximum during the day, and the minimum during the night. When stems become hard and ligneous, they lose this vital heat. Large green cotyledons gave indications of a proper heat. The hour of quotidian maximum varied from 10 A.M. to 3 P.M. in different plants.

Rameaux repeated the experiments relative to the temperature of the trunks of trees, and likewise those relating to the heat of the active vegetating parts of plants, and he came to the conclusion that the temperature of plants depends on two distinct sources—1. Organic actions going on in the young, soft, and herbaceous parts of plants, and which give rise to a temperature so slight that it requires delicate instruments to show it. 2. Meteorological influences, either immediate, as exercised on parts of plants exposed to the air, or mediate, as exercised on the soil and on the sap which is drawn up from it; the former being the most energetic. He remarks that in a tree at any one instant there are as many different temperatures as there are points unequally accessible to external sources of heat; but the sum of all these temperatures, or the entire heat of the tree, augments and diminishes with the surrounding temperature; that the variations of temperature are more rapid and more intense in the superficial than in the deep layers, and that parts having a small diameter are cooled and heated with more rapidity and energy than those whose diameter is great; that during day the temperature of the different concentric layers of a tree diminishes in going from the surface to the centre, and that this diurnal distribution is established more or less quickly and completely according to the nature of the surrounding temperature and the diameter of the tree; that during the night, on the contrary, the temperature of the different layers increases from the surface to the centre, the nocturnal distribution varying in the same way according to the surrounding temperature and the diameter; that the action of solar rays is the most powerful cause of the temperature of plants; and that the ascending sap increases or diminishes the temperature of the parts it traverses according as these parts have a temperature lower or higher than its own.

Luminosity of Plants.—Considerable differences of opinion exist as to the luminosity exhibited by plants. Light is undoubtedly given out by Fungi in certain circumstances, but the occurrence of luminous phenomena in the higher plants is still a matter of dispute. Luminosity has been noticed in many species of Agaricus growing on dead or decaying wood, such as Agaricus elearius, indigenous in the south of Europe; Agaricus Gardneri, in Goyaz, Brazil; Agaricus igneus, in the island of Amboya; and Agaricus noctilucens, in Manila. The first two are of an orange colour, the third of an ash colour, and the fourth white. The light of the Agaric of the Olive-grounds (Agaricus olearius) may be compared to that of phosphorus; it is a continued white light without scintillations, very bright when the plant is young and recently gathered. Agaricus igneus has a bluish light. The whole plant of Agaricus Gardneri gives out at night a bright phosphorescent light, somewhat similar to that emitted by the larger fire-flies having a pale greenish hue. From this circumstance, and from growing on a Palm, it is called by the inhabitants of Villa de Natividad, Flor de Coco.

Drummond describes two species of light-giving Agaricus found in the Swan River district. They grew parasitically on trunks of trees such as Banksias. When placed on paper, the Agarics emitted by night a phosphorescent light sufficient to allow a person to read by it, and they continued to do so for several nights with gradually decreasing intensity as the plant dried up. Another phosphorescent Agaric was noticed by Mr Drummond in Australia on the trunk of a dead Eucalyptus occidentalis. The upper surface of the pileus was nearly black, while the central portion and the gills were milk-white, the stipe being attached to one side of the pileus.

Some species of Rhizomorphs (which appear to be mycelia of Fungi) are remarkable for the phosphorescence which they display. These plants vegetate in dark caverns, and in the coal mines of Germany. They are seen hanging from the roof in great numbers. Their luminous qualities are most developed in the furthest recesses of the mines. Prestor has noticed that the spawn of the Truffle (Fig. 366) is luminous, and that it may thus be collected at night in the Truffle-grounds. These are instances of luminosity in living Fungi, which disappears with life. Luminosity has also been observed in plants in a state of putrefaction, as in rotten wood and in half-decayed potatoes.

Tulasne has made observations on the light given out by Rhizomorphs subterranea. By preserving it in a proper state of humidity the phosphorescence was kept up for several evenings. When the Fungus began to dry it lost its luminosity. Tulasne considers the light as similar to the phosphorescence in decaying plants, and he concludes that the same agents, namely oxygen, water, and heat, furnish the combination necessary for producing phospho- rescence, both in organized living beings and in those which have ceased to live. In both cases the luminous phenomenon accompanies a chemical reaction, which consists chiefly in the combination between organized matter and the oxygen of air, that is to say, a slow combustion, giving rise to carbonic acid.

The younger Linnaeus states that the flowers of Nasturtium, the African Marigold, the orange Lily and other orange flowers, give out, at the end of a hot summer day, intermittent phosphorescence resembling little flashes of light. Dowden also mentions a luminous appearance of a similar nature in the common Marigold (Calendula vulgaris). He noticed it on the 4th of August 1842 at 8 p.m. after a week of very dry warm weather. A gold-coloured lambeant light seemed to play from floret to floret, and to make a coarse round the disk of the flower. The light given out by flowers has been remarked by various other observers. These luminous phenomena in flowers are considered by Professor Allman as being merely optical illusions. He says they are only seen in orange and gaudy flowers, and at twilight, not in darkness, and that they must be traced to an intermittent effect on the retina.

The sap of plants is said to be luminous in certain instances. Morray describes a tree in South America called Cipo de Cunamari with a milky juice, which gave out in the dark a bright light when wounded. The phosphorescent light appeared at every cut in the stem, and each drop of the milky juice was luminous. Martius also observed the same kind of light in the sap of Euphorbia phosphorea, a Brazilian plant, when wounded. When this was observed, the temperature was 97-2° F., but it ceased when the heat sank to 68° F.; he did not find that it affected the galvanometer in the least.

**Electricity of Plants.**—Some observations have been made relative to the electricity of plants, which may be referred to at this place. Pouillet stated that electricity was developed during the ordinary process of growth in vegetables. Several pots filled with earth, and containing different seeds, were placed on an insulated stand in a chamber, the air of which was kept dry by quicklime. The stand was placed in connection with a condensing electrometer. At first no electric disturbance was manifested; but the seeds had scarcely sprouted when signs of it were evident; and when the young plants were in a complete state of growth they separated the gold leaves of the electrometer half an inch from each other. The exhalation from leaves may be considered as a cause of the development of electricity, as well as the changes effected by leaves on the oxygen and carbonic acid of the atmosphere. Plants are considered as generally in a negatively electrical state. Dr Graves thinks that in this way, in tropical climates, where the superincumbent atmosphere is rendered positively electrical by evaporation from the sea, the negative state of plants leads to thunder storms. It is said that the pith and bark, as well as the two extremities of fruits, are in opposite states of electricity.

Wartmann has made an extensive series of observations on the influence of atmospheric electricity, and that of the battery, in the development of plants; on the influence of electricity on the circulation of the sap; and on the electric currents existing in the soil and in plants. He states that there are electric currents in almost all parts of plants; that in the roots, stems, and branches, there exists a central descending current and a peripheral ascending one; that there are also lateral currents between the pith and the cambium; that the electric state of the soil, and probably also the exhalation which takes place by the organs furnished with stomata, influences the electricity of the atmosphere around. Becquerel says, that in the act of vegetation the earth acquires continually an excess of positive electricity, the bark and part of the wood an excess of negative electricity; that the leaves act like the green part of the parenchyma of the bark—that is to say, the sap which circulates in their tissues is negative with relation to the wood, to the pith, and to the earth, and positive with regard to the cambium; that the electric effects observed in vegetables are due to chemo-vital actions; and that the opposite electric states of vegetables and the earth give reason to think that, from the enormous vegetation in certain parts of the globe, they must exert some influence on the electric phenomena of the atmosphere.

**III.—VEGETABLE NOSOLOGY, OR THE DISEASES AND INJURIES OF PLANTS.**

It would be difficult to name any department of vegetable physiology concerning which so little is positively known, even to those most conversant with such matters, as the nature of the diseases to which plants are liable. The number of writings on the subject is inconsiderable, and the information afforded by them still more so. The subject, nevertheless, is one of great importance. It is intimately connected with the prosperity of our forests and the productivity of agriculture. Plants, like all other organized bodies, are subject to a great many accidents and diseases. The most common causes of disease are improper soils, ungenial climates, frosts, long-continued rains, great drought, violent storms, parasitic plants, insects, and wounds of various kinds.

According to Schleiden, plants in a state of high cultivation are all more or less in a condition predisposed to disease. There is an unnatural and excessive development of particular structures or particular substances, and thus, the equilibrium being destroyed, the plants are liable to suffer from injurious external influences. The general morbid condition produced by cultivation is heightened into specific predisposition to disease when the conditions of cultivation are opposed too strongly or too suddenly to those of nature. The outward forms of diseases are sufficiently known, but the internal appearances are less understood, and for their proper apprehension they require a knowledge of vegetable anatomy, and especially of the physiology of cells. The characters are essentially similar in all living vegetable cells. There is a wall or membrane, composed of cellulose, lined by a viscid layer (the primordial utricle), composed of an albuminous matter abounding in nitrogen; the cavity of the cell is filled with watery juice, containing little nitrogenous matter, but having all the other compounds, such as gum, sugar, vegetable acids, inorganic salts, &c., dissolved in it. The chemo-vital force of the plant appears to reside in the nitrogenous layer; all growth depends upon it, and it does not disappear until the cell-wall has become properly developed. When diseased plants are examined in the early stage, the first morbid appearance occurs in the nitrogeous layer, which becomes discoloured, coagulated, and granular, and the disease then extends to the cellular wall.

The diseases of plants may be divided in the following way:—1. Diseases which are caused by an excess or deficiency of those agents which are necessary for the vigorous growth of plants; such as soil, light, heat, air, and moisture. 2. Those which are either originally caused, or, at all events, aggravated and modified by the attacks of parasites, more particularly belonging to the natural order Fungi. 3. Those due to the action of poisons, either taken up from the soil or from the atmosphere. 4. Those caused by mechanical injuries of different kinds, as by the attacks of animals, more particularly insects. Diseases caused by changes in the atmosphere are often epidemic, and spread over extensive districts of country. Those which are due to parasitic Fungi are propagated by contagion—the minute spores being carried by the winds. Exciting causes operate with great intensity in cases where plants are previously predis- posed to disease. Thus, if a plant is in an enfeebled or weak condition, it is very liable to suffer both from epidemic and contagious diseases.

The cryptogamic diseases of plants must be considered contagious, since they are produced by the contact of one portion of organic matter with another. The contact of diseased cells produces disease in healthy cells. Thus, if a healthy plant of Cactus be inoculated with some of the fluid from a plant affected with moist gangrene, diseased action will immediately commence and extend more or less rapidly. The action is analogous to what takes place with ferment when introduced into a saccharine liquid. The liability of the plant to the development of epidemic disease is produced by the state of the atmosphere as regards moisture, the prevalence of hot or cold weather, the amount of light, and probably the electrical condition of the air and earth. The natural decay of plants also renders them liable to attacks of Fungi.

Some of the causes we have noticed may operate together in producing disease. If, from defect of nourishment in the soil, a plant is stunted or weak, it becomes predisposed to disease, and is very liable to the attacks of parasites. A sudden frost coming on in spring, after the sap has begun to flow, causes severe injury, and either kills the plant or renders it liable to disease. This occurrence is common in Britain, and is the cause why many half-hardy exotics require to be covered or kept in a dormant state until the season has advanced beyond the risk of frost. Many such plants grown on a wall with a southern exposure are stimulated by the heat of a fine day in early spring, and are thus unable to resist later frosts. Warm sun during the day, and frost at night, have proved fatal to many exotics introduced into Britain. Plants are fitted by their constitution for different climates. Some will bear a great range of temperature without injury; others can only bear a limited one. Some require a hot summer and a cold winter; others require a medium summer and a moderate winter.

It has often been stated that tender exotics may by long cultivation be made to bear the climate of Britain. It has been thought that they may become accustomed to it by degrees, and thus be acclimatized. Some have even hinted that by sowing the seeds of such plants, in the first instance, in a warm temperate region, then collecting the seeds produced by the plants and sowing them in colder districts, the species may be rendered hardy. We are constantly told that plants which, when first introduced into Britain, were put into stoves and greenhouses, are now growing in the open border freely, and that they can stand a climate which they could not do at first. Such statements do not rest on a sound basis; each species of plant bears a certain range of temperature, and we cannot extend its natural limits. The plants said to be acclimatized were not tried in the open air when first introduced, otherwise they would have been found to be hardy, without any previous process of cultivation in greenhouses. The well-known shrub Aucuba japonica was treated in a stove when first introduced, and was afterwards planted out, and found to stand our climate. This was not an instance of acclimatizing, but indicated an error regarding the constitution of the plant, which was brought from the colder parts of Japan, and was capable of enduring the cold of this climate naturally. Man did nothing in the way of changing its constitution and powers of endurance. A plant called Aponogeton distachyum flowers freely in the open pond of the Edinburgh Botanic Garden. This plant was introduced from Southern Africa, and was at first grown in stoves. A specimen was accidentally thrown into the garden pond many years ago, and there it has continued to thrive ever since, flowering during almost the whole year. The roots of the plant are deep in the water, and the pond is supplied by springs. Had it been put into the pond when first introduced, the same result would have followed. We are too apt to suppose that plants coming from countries called hot, must necessarily be stove plants; not reflecting that they may have grown in very elevated and cold regions in these countries. Such is the case with many species introduced from Chili, Nepal, and Japan. There is no evidence that plants long cultivated in this country are able to withstand our winter cold better than formerly. The Dahlia, the Heliotrope, and the Potato, are affected in the same way by frost as when they were first introduced. Long cultivation has done nothing to increase their hardiness.

Cold and bad soils are fruitful sources of disease. When plants are grown without the influence of light, they assume a white or yellowish aspect, thus becoming blanched or etiolated. In certain instances plants, even when exposed to light, present a pale and sickly hue, which is often referable to the nature of the soil, or to constitutional weakness. In many crops we observe plants having a pallid aspect owing to ungenial weather and damp soil in the first instance. The diseased state thus induced is called by Berkeley chlorosis; some have recommended for its removal the application of a weak solution of sulphate of iron along with draining. Plants, whose natural habitat is shady, become diseased when excess of light is supplied. Frosts, as well as excess of heat, render the stamens and pistils abortive. Spotting of the leaves, and canker of the stem, are often due to similar causes. When moisture is supplied in too great quantity, the plants become droopsical; and when the transpiration exceeds the absorption, the leaves often fall off. The dry and hot atmosphere of rooms often causes defoliation and disease in plants. Excessive development of hairs is sometimes a consequence of growing plants in very dry air. Diseases caused by changes in the atmosphere are often epidemic, and attack large districts of country.

The influence of the sea breeze, carrying with it saline matter, is prejudicial to most plants. Plantations are frequently injured from this cause. A good illustration is seen at Gosford, near Edinburgh, where the trees, on reaching the top of a wall, are stopped in their growth by the sea breeze, and their tops form an inclined plane proceeding inwards from the wall as a base. Some plants withstand this influence better than others.

The attacks of parasitic Fungi cause extensive injury and disease in plants. Some think that the spores of Fungi coming into contact with the plant act both as the predisposing and exciting cause of disease; others, perhaps more correctly, think that some change is first produced in the cells of the plant, which enables the spores to find a nidus, and then the disease goes on rapidly, assuming a peculiar type on account of the presence of the Fungus. In the same way as vegetable organisms found in diseases of the skin are not to be looked upon as the origin of the disease, but as being developed in textures previously morbid, and as giving often a peculiar character to the disease. Many of the diseases of cultivated crops are attributed to Fungi. The spores of Fungi are very minute, and are constantly floating in the air. They can easily be applied to the surfaces of plants. When they find an appropriate soil they send out extensive filiform ramifications which spread under the epidermis of plants, raise blisters, and finally burst forth in the form of orange, brown, and black spots constituting the fructification. They attack the stem, leaves, flowers, and fruit. Different species are restricted to different plants, and even to different parts of the same plant. The forms which the same Fungus assumes seem to vary sometimes according to the plant on which it grows.

The disease called Bunt, Smutballs, or Pepper-brand, is occasioned by the plant called Uredo Caries by De Candolle, and Uredo festida by Bauer. It attacks the grains of Wheat, and may be detected in them in their earliest state. It is represented in Figure 422. It consists of extremely minute globules of a dark colour, at first attached to a thread-like matter or mycelium. The powdery matter or spores have a disgusting odour; hence the specific name given to it. The disease is propagated by contact.

Another disease, called Smut or Dust-brand, is caused by a Fungus called Uredo segetum. It resembles the Bunt Fungus in colour and shape, but its spores are not half so large, and it does not possess a fetid odour. This Fungus destroys the ear of Corn by first causing the innermost parts of the flower to become abortive, while the pedicels on which these are seated swell and become very fleshy. The Fungus then consumes the whole of this fleshy mass, and at length appears between the chaff scales in the form of a black soot-like powder.

The disease denominated Rust, Red-rag, Red-robin, and Red-gum, is caused by a Fungus called Uredo Rubigo (Fig. 423). It forms yellow and brown oval spots and blotches upon the stem, leaf, and chaff. The spores burst through the epidermis, and are dispersed as very minute grains. The disease is common in Corn and in Grasses. Mildew is a disease caused by a Fungus denominated Puccinia graminis (Fig. 424). The ripe spore-cases of this plant are small dark-brown club-shaped bodies, their thicker end being divided into two chambers, each filled with minute spores, and their lower end tapering into a fine stalk. The sori or clusters of spore-cases burst through the epidermis sometimes in vast numbers. The minute spores seem to enter the plant by the stomata. In the Vine a kind of mildew is traced by Berkeley to the attack of a Fungus called Oidium Tuckeri. For this disease sulphur, and the pentasulphide of calcium, have been recommended as remedies.

Henslow has shown by experiment, that if the diseased seeds of Wheat be steeped in a solution of sulphate of copper, they will not produce diseased grain, and that the sulphate of copper does no injury to their germination. The solution used is one ounce of sulphate of copper to a gallon of water for every bushel of Wheat. Grain also steeped in hot water did not reproduce these fungoid diseases. In East-Lothian, with the view of preventing Smut, seed Wheat is often steeped in stale urine, and afterwards some newly slaked lime sifted on it. Sometimes a solution of salt is used as a pickle.

Ergot is a monstrous state of the grain, in which the enlarged and diseased ovary protrudes in a curved form resembling a cock's spur; hence the name, from the French ergot, meaning a spur. The ovary is black externally, spongy internally, and contains much oily matter. Some consider it as produced by the attack of a Fungus, which induces a diseased condition in the ovarian cells. The disease is usually met with in Rye, and the name of Spurred Rye is applied to it. It sometimes occurs in Wheat and in Barley, and it has also been noticed in other grains. Ergot consists of a very dense tissue formed by polygonal cells united intimately with one another, and filled with an oily fluid. It is developed in the unimpregnated ovule of Rye; for although extremely dilated by the ento-phyte, and rendered difficult of recognition, the integuments of the ovule increase without completely losing the form which they would have assumed if they had grown into a true grain. The solid mass which has been called Sclerotium Clavus by De Candolle, and the filamentous portion called Sphaecelia, by Leveillé and Fee, and Ergotia by Quekett, are only, properly speaking, organs of vegetation. The Fungus destined to grow from this apparatus is an elegant Sphaeria, probably that called by Fries Cordyliiceps purpurea.

The disease which has recently attacked the Potato in various parts of the world, is by many attributed to the attack of Fungi. This view has been strongly advocated by Berkeley, who describes the Fungus as Botrytis infestans (Fig. 425). The spores are supposed to enter the stomata, and to cause disease in the leaves in the first instance, which afterwards extends to the tubers. The effects produced on the leaves by this disease resemble much those caused by poisonous gases, such as hydrochloric, sulphurous, and nitric acids. Berkeley attributes the Potato disease entirely to Fungi. He states that the disease commenced in the leaves. They were attacked by the Mould, which ran its course in a few hours, and from the rapidity of the action the period for examination of the leaves was often passed over. The Fungus acted by feeding on the juices of plants, preventing the elaboration of the sap in the leaves, obstructing the admission of air and the emission of transpired fluids. While there is no doubt that the Botrytis is developed in the progress of the Potato disease, the question arises whether or not it is the originating cause. The view which seems to be most consonant with the phenomena is, that changes are induced in the cells of the Potato by cultivation, which render the leaves liable to disease. Atmospheric influences are thus enabled to act upon them, so as to cause alterations in their cells; and the attack of a Fungus such as the Botrytis accelerates the morbid action, and causes it to assume a peculiar form.

Crum attributed the disease of the tubers of the Potato to rupture of the starch cells and mixture of their contents with nitrogenous matter, thus causing fermentation, as in the Apple and Grape. Solly objects to the Fungus theory of Potato disease. He thinks that the disease is caused by the presence of putrefying azotized matter in the stem, just below the surface of the soil; that this is carried to all parts of the plant, causes a struggle between vital and chemical forces, and induces decomposition by a process of fermentation. The azotized matter, in a condition to act as ferment, is produced by the state of the season, by deficiency of light, and by other meteorological causes. Liebig attributed the Potato disease to diminished or suppressed transpiration depending on the hygrometric state of the atmosphere. He refers to Hales' accurate researches in regard to the Hop-blight, in which the disease is traced to the want of correspondence between absorption and transpiration, and a consequent stagnation and decomposition of the juices. The same thing, he thinks, takes place in the Potato in consequence of cold and an atmosphere loaded with moisture. Klotzsch proposes to check the Potato disease by repeatedly pinching off the extreme points of the branches and twigs. This check to the stem and branches leads, he thinks, to increased development of tubers, and strengthens the leaves and stalks. Tombeille Lomba of Namur says that he has saved Potatoes from disease by cutting off the stems, after flowering, with a very sharp sickle, and then covering the ground with earth to the depth of not less than one and a half inch. The top dressing thus applied was not disturbed until the Potatoes were ripe. The haulm was removed after being cut. It is said that the tubers acquired a good size, and were of excellent quality. If these facts are true, it would appear that, while leaves are necessary to the development of tubers, the latter, on acquiring a certain size, can continue their growth by their own proper and unassisted vitality. Bollman suggests drying the tubers at a high temperature as a remedy for the disease.

The general conclusions to be drawn from all that has been said relative to the Potato disease are, that changes are induced in the cells and vessels of the Potato by certain obscure meteorological and epidemic causes, that an alteration takes place in the cellulose and in the contents of the cells, which speedily leads to decay; that parasitic Fungi find a nidus in the decaying organic matter, so as to accelerate and give a character to the disease, and that as yet no remedy has been devised.

Dry rot is a disease to which the wood of trees is liable. It may be traced in the first instance to some alteration in the woody tissue produced by moisture or other causes, and the subsequent development of a Fungus which spreads its mycelium through the texture, and produces rapid disorganization. Trees growing in wet and ill-drained soil are subject to rot. The more abundant the albumen or sapwood, the more liable are trees to decay. The disease which has recently attacked the Larch is attributed by some to the roots reaching ungenial soil, and to the production of dry rot. In dry rot the decay takes place in the first instance in the contents of the woody tubes, and thus a suitable soil is supplied for the spores of Fungi, such as Merulius lacrymans or vastator, and Polyporus destructor. When these plants begin to grow, they spread their mycelium with great rapidity. If air is allowed to circulate freely around wood, dry rot does not attack it. But if it is placed in a damp situation without a circulation of air, then decay takes place. The spawn of the dry-rot Fungus deprives the woody tubes of their contents, for the purpose of getting the nourishment it requires, and the wood loses its consistency and toughness, the walls of the tubes becoming brittle and ruptured.

The great cause of decay in wood is moisture. Wood in a dry state may be preserved for a long time, as may be seen in the case of wood in some old buildings as Westminster Hall. To have timber in the driest state, it ought to be felled between the fall of the leaf and the spring, the nearer the former time the better. The timber of some trees is much more subject to decay than that of others. The wood of the Cypress is very durable. A great error in building is painting wood early, and thus inclosing within it the elements of decay by not allowing the escape of moisture. In olden times the wood was left bare, and exposed to currents of air which kept it dry, and hence its durability.

Various means have been proposed for preventing timber from being attacked by dry rot. Boucherie caused growing trees to absorb fluids of different kinds, which he considered as acting on the contents of the woody tubes in such a way as to render them less liable to disease. The solutions he employed were acetate of lead, pyrolignite of iron, and corrosive sublimate. He also found that trees, immediately after being cut down, when their extremities were immersed in these solutions, absorbed them with rapidity. Timber, after being cut, has been subjected to various processes for the purposes of rendering it durable. Kyanizing is performed by subjecting the wood to the action of corrosive sublimate, by means of which it is probable that the albuminous matter is coagulated, fermentation is prevented, and hence the wood is rendered less liable to decay and to the attacks of Fungi. Kyan's solution is made to pass rapidly through wood in vacuo. Sir William Burnett found that the application of chloride of zinc to vegetable matters, such as wood and canvas, had the property of effectually guarding them against all the ordinary causes of destruction, without communicating any bad property to the substance prepared from it. Canvas so acted on was kept long in damp cellars, and exposed to various vicissitudes, without being injured, while ordinary canvas in similar circumstances became rotten. The process has received the name of Burnettizing. Burnett's antiseptic solution, of one pound of chloride of zinc to five gallons of water, has been tried in Woolwich Dockyard with success. Mr Bethell uses creosote for the preservation of wood. The creosote acts by coagulating the albumen, and preventing putrefactive decomposition.

Phanerogamous parasites are also injurious to plants. Among them may be noticed especially species of Cuscuta or Dodder (Fig. 426), which prove destructive to crops of Flax and Clover. Their seeds are sown with these crops, and germinate like other plants. Ere long they become attached to the stems of the plants in their vicinity by means of suckers, and then they act as true parasites, living on the sap of the plants, and finally destroying them. Other parasites, as Broom-rapes, and Mistletoe, in a certain degree injure the plants on which they grow, but they are by no means so injurious as the Dodders. Loranthis in Guatemala, by growing on the ends of branches of trees, cause the woody matter to be developed in a horizontal manner, so as to give rise to remarkable curved processes not unlike carvings.

Many substances act as poisons to plants as well as animals. We have already given full details in regard to the effects of poisonous gases on vegetation. The experiments of Turner and Christison distinctly show that irritant gases, such as sulphurous, hydrochloric, and nitric acid, act by destroying first the parts to which they are applied, more especially those where there is abundance of moisture; while narcotic gases, like hydrosulphuric acid, have a general effect on the irritability of the plant. Marcet and Macaire experimented on the influence of fluid poisons on plants. They concluded that metallic poisons acted on vegetables in the same way as on animals. They were absorbed, and destroyed the organs to which they were applied; while narcotic vegetable poisons destroyed the whole vitality of the plants, without any local irritation.

Injurious effects are produced on plants by insects of various kinds. Some of them feed on the plants; others form habitations for themselves in the leaves and flowers; others puncture different organs with the view of depositing their ova. Earcockle, Purple, or Peppercorn, is a disease caused by a minute animal called Vibrio Tritici, or the Eel of the Wheat. The disease was noticed by Needham more than a century ago. The infected grains turn dark green. at first, and ultimately nearly black. They become rounded, resembling a small Peppercorn, but with one or more deep furrows on their surface. The husk of the chaff spreads open, and the awns are twisted. The blighted grains are full of a moist, white, cottony substance, and contain no flour. When the cottony matter is placed in a drop of water under the microscope, a multitude of minute cell-shaped animalcules are seen in active motion. They retain their vitality long. The mass may be allowed to dry, so that the slightest touch would reduce it to powder, and yet, when moistened with water, the animalcules will revive and become active. They may be dried and revived many times before they are killed.

Many trees, especially the Oak and Willow, are liable to the disease called Galls, which is due to attacks of insects (species of Cymps, &c.). The insects wound the bark and leaves while depositing their ova, and the irritation causes a formation of a deposit around them. The galls of commerce are produced on Quercus infectoria. In blue galls the insect is still in the interior, while in white galls the insect has escaped by a perforation. The Oak spangle is an appendage of the leaf attached by a central point to its under surface; the inner side is smooth, the outer red, hairy, and fringed. Each contains a single insect, which retains its habitation till March, long after the leaves have fallen to the ground. These spangles resemble parasitic Fungi in their appearance, and have often been mistaken for them. The species of Spruce (Abies) are liable to a peculiar disease produced by the attacks of an insect called Adelges Abietis. This disease consists of an alteration in the colour and form of the leaves, which are aggregated together in the shape of cone-like excrescences.

The remedies proposed for the attacks of insects are numerous. Quick-lime, Sulphur, Turpentine, Tobacco, have all been recommended. In the case of Aphides the vapour of Tobacco is useful. It is not easy to get rid of the species of Coccus with their cottony covering. The only remedy seems to be the cleaning of the leaves and other parts of the plant by the hand. The vapour of sulphur will kill many insects, but then it acts injuriously on plants. A solution of Tobacco, the crushed leaves of the Cherry Laurel which give out a hydrocyanated vapour, ammoniacal liquor, coal tar, and many other substances, have been employed in different instances.

PART II.

TAXOLOGICAL BOTANY, OR THE CLASSIFICATION OF PLANTS.

CHAPTER I.

GENERAL REMARKS ON CLASSIFICATION.

In examining the Vegetable Kingdom, we observe that the individuals composing it are formed by the Almighty in accordance with a principle of order, as well as a principle of special adaptation. We have already remarked the order pursued in the arrangements of the various parts of the root, stems, leaves, and flowers of plants, and we have traced, in some degree, the modes in which they are fitted to perform their different functions. We now proceed to apply the facts of Vegetable Anatomy and Physiology to the classification of plants, and to consider the plan according to which they are grouped together in classes and families.

We see around us various kinds or sorts of plants which more or less resemble each other—or, in other words, are more or less related to each other. In Taxological or Systematic Botany we endeavour to mark these resemblances, and to determine their relations. It is impossible to give a scientific arrangement of the plants of the globe without a thorough knowledge of structure and morphology, and without an extensive acquaintance with the vegetation of all parts of the world. We cannot expect to determine the system on which plants have been grouped until we are familiar with all the forms which they present. Hence, in the present state of our knowledge, there must be imperfection in our attempts at systematizing. The Floras of many regions in Africa, India, China, Australia, and America, are still unknown, and we may therefore conclude that in all systems there will be gaps to be filled up as our knowledge increases. Sufficient, however, is known to enable us to group plants according to certain evident alliances.

The necessity for arrangement is evident, when we reflect that there are more than 120,000 known species of plants on the earth. In order to make these available for scientific purposes, it is absolutely essential that they should be named and classified. In associating plants in certain groups we naturally proceed on an idea of resemblance or likeness. While in ordinary language this idea is vague, and is often founded on imperfect data, it is clear that in science it must be strict and rigorous. It is not enough to say that one plant resembles another in its general aspect, we must ascertain the particulars of agreement, and the points in which they differ; we must weigh well the importance of the characters, and must compare organs which are equivalent in value; and thus we shall often find, that plants which to common observers appear alike, are in reality totally different. The study of organography gives us a strict and accurate technical language which must be rigidly adhered to in classification.

Plants as they occur in nature are viewed as individuals resembling or differing from each other. Some individuals are so decidedly alike, that we at once give them the same names. Thus a field of Wheat is composed of numerous similar individuals which can be separated from each other, but cannot be distinguished by any permanent or marked difference. Although there may be some difference in size and other minor points, still we at once say they are stalks of Wheat. Every grain of Wheat when sown produces a stalk of Wheat; these stalks yield grains which produce individuals like their parents. The shoots or buds given off from the base of Wheat by tillering, also produce stalks of Wheat. On such universal and inevitable conceptions as these, our idea of Species is founded.

A Species may be defined as an assemblage of individuals presenting certain constant characters in common, and derived from one original protoplast or stock. The individuals are thus considered as having arisen from one parent stock. They may differ slightly in size, or in colour, and other unimportant respects, but they resemble each other more closely than they resemble any other plants, and their seeds produce similar individuals. Observation and common daily experience demonstrate, in the actual circumstances in which we exist, the permanence of the types which constitute the species of living bodies. There is no evidence whatever of a transmutation of species. The erroneous statements regarding the conversion of Oats into Rye have proceeded on imperfect observations. The individuals, however, of a species may present certain differences in regard to size, colour, &c., these differences depending on soil, and on different conditions of heat, light, and moisture. Such differences are not incompatible with the idea of a common origin, and moreover, there is always a tendency to return to the original type. What are called Varieties, therefore, are variations in species which are not in general of a permanent character, and cannot be kept up in ordinary circumstances by seed. By cultivation, however, such varieties are sometimes perpetuated. This is usually accomplished by means of cuttings or grafts, and in certain instances even by seed. Thus the varieties of the cereal grains and of culinary vegetables have been propagated so as to constitute permanent races.

Plants which are cultivated are liable to sport, as it is called, and the peculiarities and variations thus produced are sometimes kept up. All the varieties of Cabbage, Cauliflower, Brocoli, Savoys, and Curled Greens are derived from one stock, Brassica oleracea. This plant grows wild on the sea-shore, and when cultivated it undergoes remarkable changes. Thus it forms a heart, as in ordinary Cabbage; its flower-stalks become thickened and shortened, as in Cauliflower and Brocoli; or its parenchyma is largely developed between the vessels, so as to give rise to the crisp and curled appearance of Greens. This tendency in the plant to produce monstrousities was early noticed by cultivators, and care was taken to propagate those individuals which showed abnormal appearances. The seeds of such were saved, put into good soil, and no plants were allowed to remain except such as presented the required form. In this manner certain races of culinary vegetables have been established. If, however, these cultivated plants are allowed to grow wild and scatter their seed in ordinary soil, they will in the progress of time revert to the original type or species. Instances such as these show the remarkable effects of cultivation in perpetuating varieties by seed.

In regard to the cereal grains, Wheat, Barley, Oats, &c., they have been so long cultivated that we are at a loss to know the original types or species. We have been forced, in the mean time, to call them species, although they are probably mere cultivated varieties of unknown species, perpetuated as races. That Wheat is an abnormal state of some plant, it has been remarked, might be conjectured from the fact that it does not become wild; if left to itself it disappears. Fabre has stated recently that the Wheat is a cultivated variety of the grass called Egllops ovata. This plant first undergoes a change by which it becomes what has been called Egllops triticoides, and then in successive years is converted into true Wheat. This discovery, as Lindley says, does not invalidate the characters by which the genera Egllops and Triticum (as taken from wild species, such as Triticum maritimum, &c.) are separated, any more than the existence of a Poloria in Linaea invalidates the characters derived from the distinction between regular and irregular flowers.

It is of great importance to distinguish between mere varieties and true species, and to determine the limits of variation in different species. By not attending to this, many varieties have been described as species, and by their change or disappearance have given rise to great confusion and correctness both in descriptions and in arrangements. Another source of fallacy arises from hybrids being occasionally reckoned as true species.

Certain species not identical in origin, have common features of resemblance, and are associated together under what is called a Genus. A genus, then, is an assemblage of nearly related species, agreeing with one another, in general structure and appearance, more closely than they accord with other species. Thus the Scotch Rose, the Dog Rose, the China Rose, and the Sweet-briar, are all different species included in one genus, Rosa. It may happen that a single species may be reckoned as forming a genus, when the peculiarities are as marked as those constituting other genera. Thus, if there was only one species of Oak, it would be sufficient to constitute a genus, as much so as at present when it includes 200 species. It is distinguished by its acorn from other allied genera, such as the Beech, the Hazel, and the Chestnut. The species in a genus present one general plan, and may be said to be formed after the same pattern. Some species of a genus, having special points of resemblance, may be grouped together in a Sub-genus.

On looking at genera, it will be seen that some of them, such as Oaks, Hazels, Beeches, and Chestnuts, have a strong resemblance or family likeness, and that they differ remarkably from such genera as Firs and Pines, Maples and Ashes. Certain genera may in this way be grouped so as to form Orders or Families. While genera are groups of allied species, Orders are groups of allied genera, or, in reality, more comprehensive genera. Thus, Firs, Pines, and Larches, belong to different genera, but all agree in being cone-bearing, and are grouped under Coniferae. The Rose, the Raspberry, the Bramble, the Strawberry, the Cinquefoil, the Cherry, and the Plum, all agree in their general organization, and are united under Rosaceae. Certain genera have more points in common than others, and are grouped together under sub-divisions of orders called Sub-orders. Thus, the Plum and the Cherry have a drupe as their fruit, and are more nearly allied to each other than they are to the Apple; again, the Strawberry, Raspberry, and Bramble, are more allied to each other than to the Cherry or Apple. We have thus Sub-orders of Rosaceae, namely, Amygdalaceae, including the Plum, Peach, Cherry, and Almond; Pomeae, including the Apple, Pear, Medlar, and Quince; Potentillaceae, including the Strawberry, Cinquefoil, and Raspberry; and Roseae, comprehending the Roses.

Certain orders agreeing in evident and important general characters are united together so as to form Classes; and subdivisions of classes are made in the same way as in the case of orders. There are thus Sub-classes associating certain orders included in one Class. The usual divisions are Classes, Orders, Genera, and Species. These occur in all systems of classification. A more minute subdivision may be made as follows:

1. Classes. a. Sub-classes. 2. Orders or Families. a. Sub-orders. b. Tribes. c. Sub-tribes.

III. Genera. a. Sub-genera or Sections.

IV. Species. a. Varieties.

An enumeration of the marks by which one Class, Order, Genus, or Species is distinguished from another is called its Character. In giving the characters of any division, we notice merely those which are necessary to distinguish it from others. This is called its Essential Character. A plant may also be described completely, beginning at the root, and proceeding to the stem, branches, leaves, flowers, fruit, seed, and embryo. This is not essential, however, for the purposes of classification, and would be quite superfluous in that point of view. In the character of the Classes the important points of structure on which they are constituted are given. In the character of Orders (the ordinal character) we give the general structure of the included plants, especially of their flowers and fruit. In the Generic character, we notice the modification of the ordinal character in a given genus—the character being taken from the parts of the flower and fruit, as in the order. In the Specific character are included certain less important modifications of form, whether in the stem, leaves, or flowers, which serve to distinguish allied species.

The essential character of a genus, when given in Latin, is put in the nominative case, that of a species in the ablative. The names of the Classes are variously derived, ac- Botany.

According to the views of the authors in regard to the classification. They express some points of structure or development which are of marked importance or permanence. The Orders are named from some characteristic genus included in them, except in artificial methods, where some organ is taken as the means of distinction. Genera are derived either from the Latin name of one of the species, from the structure or qualities of the included species, or from the name of some botanist, &c. Thus Prunus is a genus including the Plum, the Sloe, &c.; Rosa, the Rose; Papaver, the Poppy; Hookeria is a genus named after Hooker; Lithospermum, from two Greek words signifying a stone and seed, is given to a genus, the species of which have hard stony nuts or achenes.

In giving the name of a plant we mention its genus and species. Thus the common Dog-rose is called Rosa canina, the first being the generic name, the second the specific. Specific names may indicate the country in which a plant is found, the locality in which it grows, the form of its roots, stem, or leaves, the colour of its flowers, &c. A species named in honour of its discoverer or describer has the specific name usually in the genitive, as Veronica Jacquinii, named after Jacquin. When the name is given in compliment to a botanist, without reference to the discovery, then the specific name is in the adjective form, as Veronica Lindleyana. Sometimes a generic name is used specifically, and then it is put as a noun after the genus, with a capital letter, and the two names may not agree in gender; thus we have such names as Crataegus Oxyantha, Æthusa Cynapium, Viburnum Opulus, Veronica Chamaedrys. To the genus and species are added certain letters, indicating the botanist who founded them. Thus Valeriana L. is the genus Valerian, as constituted by Linnæus, and Valeriana officinalis L. is the officinal Valerian, as described by Linnæus; Oxytropis, DC., is the genus so called by De Candolle. Sometimes authors happen to describe the same plant by different names. It is of importance, therefore, to give the Synonyms of other botanists, with their names. Thus Salvadora persica of Garcin is S. Wightii of Arnott, and S. indica of Wight's Illustrations. After the description of a plant we usually mention its Habitat, that is, the country or province in which it grows, with the nature of the locality, whether alpine or lowland, dry or moist, &c.

The following are some of the common abbreviations and symbols used by botanists:

The names of Authors are abbreviated in Botanical works, by giving the first letter or syllable, &c.—Thus, L. stands for Linnæus; DC. for De Candolle; Br. for Brown; Lam. and Lamk. for Lamarck; Hook. for Hooker; Hook. fil. for Hooker junior; Lindl. for Lindley; Arn. for Arnott; H. and R. for Humboldt and Bonpland; H. B. and K. for Humboldt, Bonpland, and Kunth; W. and A. for Wight and Arnott; Berk. for Berkeley; Bab. for Babington, &c.

The symbol oo or oo means an indefinite number; in the case of stamens, it means above 20.

O O O or A. means an annual plant. O O O O or B. means a biennial plant. 2f A or P. means a perennial plant. S or Sh. means a Shrub; T. a Tree.

) turning to the left; ( turning to the right.

o = Cotyledons incumbent, radicle lateral. o = Cotyledons incumbent, radicle dorsal. o = Cotyledons conduplicate, radicle dorsal. o = Cotyledons plicate or folded twice, radicle dorsal. o = Cotyledons folded thrice, radicle dorsal.

Hermaphrodite flower, having both stamens and pistil. ♂ Male, staminiferous, staminate, or sterile flower. ♀ Female, pistilliferous, pistillate, or fertile flower. ♂♀ Unisexual species, having separate male and female flowers. ♂♀ Monoeious species, having male and female flowers on the same plant.

CHAPTER II.

SYSTEMS OF CLASSIFICATION.

There are two systems pursued in the arrangement of plants; one is called the Artificial method, and the other the Natural method. In both of them the genera and species, or the minor divisions, are the same, but the higher divisions of classes and orders are totally unlike, and are founded on entirely different principles. The genera and species are very differently arranged in the two systems. In artificial methods one or two organs are selected in an arbitrary manner, and they are taken as the means of forming classes and orders; while in the natural method plants are grouped according to their alliance in all their important characters. Plants belonging to the same class and order in the former system may have nothing in common except the number of stamens and pistils, or the form of their flowers, or some other arbitrarily selected character; while in the latter, plants in the same class and order are related by true affinity, and correspond in all the essential points of their structure and organography. When a student knows the artificial class and order to which a plant is to be referred, he does not thereby become acquainted with its structure and properties; plants diametrically opposed in these respects may be associated together. When he determines, on the other hand, the place of a plant in the natural system, he necessarily acquires a knowledge of its structural relations and affinities. Hence a knowledge of the latter system is that which must be the aim of every botanical student.

L.—ARTIFICIAL SYSTEMS OF CLASSIFICATION.

Attempts at an artificial methodical arrangement of plants were made by Cesalpino, Morison, Rivinus, and Tournefort, but the system which was most universally adopted was that of Linnæus, which was founded on the sexes of plants, and hence has been denominated the sexual system. It is called an artificial method because it takes into account only a few marked characters in plants, and does not propose to unite them by natural affinities. It is an index to a department of the book of nature, and as such is useful to the student. It does not aspire to any higher character, and although it cannot be looked upon as a scientific and natural arrangement, still it has a certain facility of application which commends it to the tyro. In using it, however, let it ever be remembered, that it will not of itself give the student any view of the true relations of plants as regards structure and properties, and that by leading to the discovery of the name of a plant, it is only a stepping-stone to the natural system.

In the artificial system of Linnæus, plants are divided into Flowering and Flowerless—the latter being included in the twenty-fourth class, under the name of Cryptogamia, and The following are the Classes and Orders of the Linnaean artificial system:

A. Flowering Plants, Phanerogamia.

I. Stamens and Pistils in every flower.

1. Stamens unconnected.

a. Stamens either of equal length, or at all events neither didynamous nor tetradynamous:

| Number | Class | Order | Styles | |--------|-------------|---------|--------| | 1 | Monandria | I | | | 2 | Diandria | II | | | 3 | Triandra | III | | | 4 | Tetandra | IV | | | 5 | Pentaandra | V | | | 6 | Hexandra | VI | | | 7 | Heptandra | VII | | | 8 | Octandra | VIII | | | 9 | Enneaandra | IX | | | 10 | Decandra | X | | | 12 to 19 | Dodecandra | XI | | | 20 or more | Hypogynous | XII | |

b. Stamens differing in length in certain proportions:

| Length | Class | Order | Fruit | |--------|-------------|---------|-------| | Long | Didynamia | XIV | Achenes | | Short | Tetradynamia| XV | Capsular |

2. Stamens connected—

By their Filaments in one parcel or tube

| Class | Order | Stamens | |-------------|---------|---------| | Monadelphia| XVI | | | Diadelphia | XVII | | | Polyadelphia| XVIII | |

By their Filaments in two parcels

| Class | Order | Stamens | |-------------|---------|---------| | Triandra | Order I | 3 | | Pontandra | | 5 | | Decandra | | 10 | | Polyanthera | | Numerous |

By their Filaments in three or more parcels

| Class | Order | Stamens | |-------------|---------|---------| | Monandra | Order I | 1 | | Diandra | | 2 | | and so on as in the first 13 Classes |

With the Pistil on a column

| Class | Order | Stamens | |-------------|---------|---------| | Gynandra | XX | |

II. Stamens and Pistils in separate flowers.

On the same Plant

| Class | Order | Stamens | |-------------|---------|---------| | Monoclea | XXI | | | Dioecia | XXII | |

On separate Plants

| Class | Order | Stamens | |-------------|---------|---------| | Monoclea | XXI | | | Dioecia | XXII | |

III. Stamens and Pistils in the same and in separate flowers on the same or on separate Plants

| Class | Order | Stamens | |-------------|---------|---------| | Polygamia | XXIII | |

B. Flowerless Plants.

Organs of reproduction inconspicuous

| Class | Order | Stamens | |-------------|---------|---------| | Cryptogamia | XXIV | |

The system of Linnaeus, even when regarded simply as an index to the vegetable kingdom, is by no means complete. The parts of flowers often vary in number, and cannot be confined within the strict rules required by this method of arrangement; moreover, unless the stamens and pistils are perfect and complete, and the plant is in full flower, it is impossible to determine its class and order. When the system is rigidly adhered to, we find that species belonging to the same genus are separated. Thus the genus Lychnis has most of its species hermaphrodite, with ten stamens and five styles, but there is at least one British species dioecious. In order, therefore, to keep the genus... Botany.

entire, and not separate the species, Linnæus adopted the plan of putting Lychins in the class Decandra and order Pentagynia, and under the class Diœcia order Decandra, placing the name of the dioecious species, and referring the student to the 10th class for a description. In this way the genera—which are founded on natural affinities, and are not constructed by a mere arbitrary method—are preserved in their integrity. All the species of one genus are placed together, whether they accord or not with the characters of the class and order; the place of the genus being determined by the characters of the majority of the species. The names of the anomalous species are given in italics, in the classes and orders to which they belong according to the Linnæan method, and reference is made to the description of them as given under the genus.

II.—NATURAL SYSTEM OF CLASSIFICATION.

In arranging plants according to the Natural System, the object is to bring together those which are allied in all essential points of structure. It is called natural, because it proposes to follow the system of Nature, and thus takes into account the true affinities of plants on a comparison of all their organs. One of the first natural methods of classification was that proposed by Ray about 1682. He separated flowering from flowerless plants, and divided the former into Dicotyledons and Monocotyledons. His orders were founded on correct views of the affinities of plants, and he far outstripped his contemporaries in his enlightened views of arrangement. He may be said to have laid the foundation of that system which has been elucidated by the labours of Jussieu, De Candolle, Brown, Lindley, Endlicher, and others.

In arranging plants according to a natural method, we require to have a thorough knowledge of structural and morphological botany, and hence we find that the advances made in the latter departments have materially aided the efforts of systematic botanists. We may regard plants in various points of view, either with reference to their elementary tissues, their nutritive, or their reproductive organs. The first two are the most important, as being essential for the life of individuals, while the latter are concerned in the propagation of the species. These sets of organs bear a certain relation to each other, and we find that plants may be associated by a correspondence in all of them. In comparing the characters of plants, we must take care that we contrast organs belonging to the same class of functions, and the value of the characters must depend upon the importance of the functions performed by the organs.

Cellular tissue is reckoned of the highest value, as being of universal occurrence, and as carrying on, in many instances, all the functions of plants. In considering the elementary tissues alone, we divide all plants into Cellular and Vascular—the former including the lower tribes, such as Lichens, Seaweeds, and Mushrooms, the latter including the higher flowerless plants with scalariform vessels, and all the flowering plants with spiral vessels. In the nutritive and reproductive organs there is nothing which can be considered of the same value as cellular tissue. In the nutritive organs the embryo occupies the highest place, and by examining it we divide plants into Acotyledonous, having no cotyledons, but occasionally producing a prothallus; Monocotyledonous, with one cotyledon; and Dicotyledonous, with two cotyledons. Proceeding to the secondary organs in the nutritive class, we find that the root gives rise to the divisions of Heterorhizal, Endorhizal, and Exorhizal of Richard. Next the stem is Cellular or Thallogenous, Acrogenous, Endogenous, and Exogenous. The thallus is veinless, the front of Acogens has often a forked venation, the leaves of Endogens are parallel-veined, and those of Exogens reticulated. In the reproductive system the stamens and pistils occupy the highest place, as being the essential organs of flowering plants (Phanerogamia), while antheridia and archegonia have the same value in flowerless plants (Cryptogamia). Succeeding these organs in value comes the fruit, which is either a theca with spores, or a pericarp with seed. The floral envelopes are the next in the series; they are absent in Cryptogamous plants, and present in Phanerogamous; their arrangement is ternary in Monocotyledons, quinary and quaternary in Dicotyledons. The inflorescence and bracts, as found in flowering plants, occupy the lowest place in the subordination.

We thus find, that by comparing these different organs in plants, we arrive at certain great natural divisions, including plants which are associated by affinity of structure and function, as exhibited in the following table:

| Cellular Plants without Vessels or Stomata | Vascular Plants with Scalariform Vessels, and Stomata | Vascular Plants with Spiral Vessels, and Stomata | |-------------------------------------------|------------------------------------------------------|--------------------------------------------------| | Acotyledonous | Acotyledonous with Prothallus | Monocotyledonous | | Heterorhizal | Heterorhizal | Endorhizal | | Thallogenous | Acrogenous | Exorhizal | | No Venation | Forked Venation | Parallel Venation | | Cryptogamous | Cryptogamous | Phanerogamous | | Thence with Spores, or naked Spores | Thence with Spores | Angiosperms or Gymnosperms | | Flowerless | Flowerless | Floral Envelopes | | No Inflorescence nor Bracts | No Inflorescence nor Bracts | Having Inflorescence and Bracts |

It is impossible to represent the affinities of plants in a linear series. Different groups touch each other at several different points, and must be considered as alliances connected with certain great centres. We find also that it is by no means easy to fix the limits of groups. There are constantly aberrant orders, genera and species, which form links between the groups, and occupy a sort of intermediate territory. In this, as in all departments of natural science, there are no sudden and abrupt changes, but a gradual transition from one series to another. Hence exact and rigid definitions cannot be carried out. In every natural system there must be a certain latitude given to the characters of the groups, and allowance must be made for constant anomalies, in as far as man's definitions are concerned.

Having examined the general principles upon which the natural system is founded, we shall now give a sketch of some of the more important Taxiological plans which have been propounded. Jussieu divided plants into three primary groups—Acotyledones, Monocotyledones, and Dicotyledones, and included under them fifteen classes. One of the classes is Acotyledonous, three Monocotyledonous, and eleven Dicotyledonous. The three Monocotyledonous classes are distinguished by the position of the stamens, whether inserted on the thalamus (hypogynous), attached to the calyx (perigynous), or to the ovary (epigynous). Dicotyledonous plants are divided into Apetalous (monochlamydeous), plants having a calyx only; Monopetalous (gamopetalous), plants having united petals; Polypetalous, plants having separate petals; and Dichnous, plants which are unisexual and incomplete; the last constitutes the fifteenth class, while the other ten classes of Dicotyledons included in the other three divisions are determined chiefly by the position of the stamens and the corolla in relation to the ovary. Under these classes he included 100 orders. Tabular View of De Candolle's Natural System.

A. VASCULARES OF COTYLEDONE.

Class I. Dicotyledones or Exogenae.

Sub-class I. Thalamiflora. Petals distinct, stamens hypogynous.

Sub-class II. Calyciflora. Petals distinct or united, stamens perigynous or epigynous.

Sub-class III. Corolliflora. Petals united, hypogynous, usually bearing the stamens.

Sub-class IV. Monocheilum. Having a calyx only, or no floral envelope.

B. ACOTYLEDONES OR CELLULARES.

Sub-class I. Foliosae. Having leaves.

Sub-class II. Aphyllae. Leafless.

The following is the arrangement adopted by Lindley in his recent work on the Vegetable Kingdom:

Class I. THALLOGENAE—Asexual or Flowerless plants without proper stems or leaves, such as Fungi.

Class II. ACROGENAE—Asexual Flowerless plants, with stems and leaves, such as Ferns.

Class III. RHIZOGENAE—Sexual or Flowering plants, with Acotyledonous embryos and fructification springing from a thallus, such as Rafflesia.

Class IV. ENDOGENAE—Monocotyledonous flowering plants with Endogenous stems, parallel venation, and ternary symmetry. This class is subdivided into four sections:

1. Plants with glumaceous flowers formed by imbricated bracts, such as Grasses. 2. Petaloid unisexual flowers, such as Palms. 3. Petaloid hermaphrodite flowers adherent to the ovary, such as Narcissus. 4. Petaloid hermaphrodite flowers free from the ovary, such as the Lily.

Class V. DICTYOGENAE—Monocotyledonous plants with reticulated venation, including such orders as Dioscoreaceae and Smilacaceae.

Class VI. GYMNOCOGENAE—Polycotyledonous Exogens with naked seeds, as Coniferae and Cyadaeaceae.

Class VII. EXOGENAE—Dicotyledonous plants with seeds in a seed-vessel. Under this class he puts the following sub-classes:

Sub-class I. Diclinous Exogens, or Dicotyledons with unisexual flowers, and no tendency to form hermaphrodite flowers, such as Amentiferae.

Sub-class II. Hypogynous Exogens, or Dicotyledons with hermaphrodite or polygamous flowers, and stamens entirely free from the calyx and corolla, such as Ranunculaceae.

Sub-class III. Perigynous Exogens, or Dicotyledons with hermaphrodite or polygamous flowers, the stamens growing to the side of either the calyx or the corolla, ovary superior, or nearly so, such as Rosaceae.

Sub-class IV. Epigynous Exogens, or Dicotyledons with hermaphrodite or polygamous flowers, the stamens growing to the side of either the calyx or corolla, ovary inferior, or nearly so, such as Umbelliferae.

The following is the arrangement which we propose to follow—De Candolle's system being taken as the basis, and some of the divisions being derived from Jussieu and Lindley:

Class I. DICOTYLEDONES, EXOGENAE, or ACAMPHIBRYA, in which spiral vessels are present; the stem is exogenous; stomata are present; the venation of the leaves is reticulated; the flowers have stamens and pistils, and the symmetry is quinary or quaternary; the ovules are either in an ovary or naked; and the embryo is dicotyledonous. In this class there are included four Sub-classes:

Sub-class I. THALAMIFLORE.—Flowers usually dichlamydeous, petals separate, inserted on the thalamus, and stamens hypogynous.

Sub-class II. CALYCIFLORE.—Flowers usually dichlamydeous, petals either separate or united, stamens either perigynous or epigynous. This sub-class has two subdivisions:

1. Polypetalae or Dialypetalae—in which the petals are separate. 2. Monopetalae or Gamopetalae—in which the petals are united.

Sub-class III. COROLLIFLORE.—Flowers dichlamydeous, petals united, corolla hypogynous. In this sub-class there are two subdivisions:

1. Hypostaminaceae—in which the stamens are inserted into the receptacle and not united to the corolla. 2. Epicorolla or Epipetalae—in which the stamens are inserted on the corolla.

Sub-class IV. MONOCHAMYDEAE, or APETALE—flowers either with a calyx only or achlamydeous. In this sub-class there are two subdivisions:

1. Angiospermae—in which the ovules are contained in a pericarp, and are fertilized by the action of the pollen on the stigma. a. Spermogonae, having true seeds and a cotyledonous embryo. b. Sporogonae, having spore-like seeds and an acotyledonous embryo. 2. Gymnospermae—in which the ovules are not contained in a true pericarp, and are fertilized by the direct action of the pollen without the intervention of a stigma, and the embryo is acotyledonous.

Class II. MONOCOTYLEDONES, ENDOGENAE, or AMPHIBRYA, in which spiral vessels are present; the stem is endogenous; stomata occur; the venation is usually parallel, sometimes slightly reticulated; the flowers have stamens and pistils, and the symmetry is ternary; the ovules are contained in an ovary; the embryo is monocotyledonous. Under this Class are included three Sub-classes: Sub-class I. Dicotyledoneae—plants with reticulated venation in their leaves.

Sub-class II. Petaloidae, or Florideae—in which the leaves are parallel-veined; the flowers usually consist either of a coloured perianth or of whorled scales. This sub-class is divided into—

1. Epigynous—in which the Perianth is adherent, the ovary is inferior, and the flowers are usually hermaphrodite.

2. Hypogynous—in which the Perianth is free, the ovary is superior, and the flowers are usually hermaphrodite.

3. Incompleta—flowers incomplete, often unisexual, with no proper perianth, or with a few verticillate scales.

Sub-class III. Gumniferae—flowers glumaceous, consisting of infertile or sterile venation parallel.

Class III. Acotyledones, or Acrogeneae, and Thallophyta and Acrobrya, in which the plants are either entirely cellular, or consist partly of scleriform vessels; the stem when woody is Acrogeneae; stomata occur in the higher orders; the leaves are either veinless or have a forked venation; no flowers are present; the reproductive organs consist of Anthidia and Archaeonia; spores or cellular embryos are produced which have no cotyledons. Under this class there are two divisions:

Sub-class I. Acrogeneae, Acrobrya, or Cormogeneae—with a distinct stem, bearing leaves or branches.

Sub-class II. Thallogeneae, Thallophyta, or Cellularae—having no distinct stem nor leaves, but forming a cellular expansion of various kinds which bears the organs of reproduction.

CHAPTER III.

ARRANGEMENT AND CHARACTERS OF THE NATURAL ORDERS.

Having now considered the primary divisions of the natural system, we proceed to give the characters of the natural orders, which are associated under the different classes and sub-classes. We have already stated, that in a linear series it is impossible to group the orders according to their affinities. Each order is allied, not merely to those which immediately precede and follow it in such a series, but to various other orders which are necessarily removed from it. On the confines of classes and sub-classes, orders occur which have characters common to two or more of the groups, and we constantly meet with aberrant genera which form a connecting link between two orders. In Botany, as in all departments of natural science, there are no rigid lines of demarcation, but one division seems to pass into another by an insensible gradation. Our definitions express the most marked and important characters of the groups, without attempting to embrace all the anomalies; and as our knowledge of the vegetation of the globe advances, we are enabled to improve the definitions of the groups, and to form intermediate divisions.

I.—Phanerogameae, Cotyledoneae, or Flowering Plants.

Class I.—Dicotyledones, Exogeneae, or Acramphibrya.

Sub-class I.—Thalamiflore.

Natural Order 1.—Ranunculaceae, the Buttercup order (Figs. 427 to 429).—Herbs, rarely shrubs, with an acid watery juice, and generally with much-divided, exstipulate leaves, the petioles of which are dilated, and sheathing (Figs. 117, 118, and 120). Sepals 3-6, usually deciduous, sometimes deformed. Petals 3-15, sometimes anomalous (Figs. 214, 215, 216), at other times suppressed. Stamens usually 3, with adnate anthers (Fig. 428). Carpels numerous, one-celled (Figs. 181 and 277), or united into a single, many-celled pistil. Fruit, achenes (Fig. 317), follicles (Fig. 298), or baccate. Seeds anatropal, with horny albumen, and a minute embryo (Fig. 429). The plants of this order characterize a cold, damp climate, and when met with in the tropics, they occur on the sides and summits of mountains. They have narcotic-acrid properties, and are usually more or less poisonous. The acridity varies at different seasons, and in different parts of the plant; it is frequently volatilized by heat, and destroyed by drying. Among the plants of this order may be noticed Aconitum Napellus, Monkshood, used to allay pain in neuralgia; Delphinium Staphysagria, Stavesacre; Helleborus officinalis (the black Hellebore of the ancients), H. niger, feroxius,* and PL CX. other species, famed as drastic purgatives; and Podophyllum peltatum, May-apple, used in North America as a cathartic.

Nat. Ord. 2.—Dilleniaceae, the Dillenia order.—Trees, shrubs, or under-shrubs, with alternate, exstipulate leaves, five persistent sepals in two rows, five deciduous imbricated petals, indefinite stamens often turned to one side, a 2-5-carpellary apocarpous or syncarpous fruit, arillate anatropal seeds, and homogeneous albumen. The species occur chiefly in Australasia, India, and Equinoctial America. They have astringent qualities, and some of them are large trees, which afford excellent timber.

Nat. Ord. 3.—Magnoliaceae, the Magnolia order (Fig. 430).—Trees or shrubs, with alternate coriaceous sometimes dotted leaves, and convolute stipules, which cover the buds, and are deciduous. They are remarkable for the beauty of their foliage, and the fragrance of their flowers. Sepals, usually 3-6, deciduous. Petals, three or more, imbricated. Stamens 3, distinct, with adnate anthers. Carpels, one-celled, numerous, on an elevated receptacle. Fruit, of numerous, dry or succulent, dehiscent or indehiscent, carpels. Seeds often arillate, and suspended from the fruit by a long funicle; albumen fleshy and homogeneous; embryo minute. Magnolias abound in North America. The plants of this order have bitter, tonic, and aromatic qualities. Drimys Winteri* yields Winter's bark; Illicium anisatum, on account of its flavour and the stellate arrangement of its fruit, receives the name of Star-Anise, Liriodendron tulipifera is the Tulip-tree (Fig. 430), remarkable for its abrupt or truncated leaves.

Nat. Ord. 4.—Anonaceae, the Custard-apple order.—Trees or shrubs with alternate, entire, exstipulate leaves, three persistent sepals, six petals in two rows, usually valvate in... Botany.

testivation, sometimes combined, numerous stamens covering a large hypogynous receptacle, numerous carpels containing one or more ovules, a succulent or dry fruit, consisting of a number of one or many-seeded carpels, distinct or combined, seeds with a brittle spermoderm, ruminant albumen, and a minute embryo. The species occur in tropical regions, and many of them furnish valuable fruits. The plants of this order are generally aromatic and fragrant. *Anona squamosa* yields the sweetsop, *A. muricata* the sour-sop, and *A. reticulata* the netted Custard-apple; *A. Cherimolia* produces the Peruvian Cherimoye, said to be one of the finest fruits known.

Nat. Ord. 5.—Schizandraceae, the Schizandra order.—Trailing shrubs, with alternate exstipulate leaves, allied to Anomoeae, but differing in their habit, their unisexual flowers, their imbricate testivation, and their homogeneous albumen. The stamens are often monadelphous, and the fruit consists of numerous baccate carpels. The species occur in India, Japan, and the hotter parts of North America.

Nat. Ord. 6.—Menispermaeae, the Moon-seed order.—Trailing shrubs with alternate, simple, usually entire leaves, and unisexual (often dioecious) flowers. Symmetry generally ternary. Stamens distinct or monadelphous, and attached to an androphore. Carpels supported on a gynoecium, one-celled, containing a single curved ovule. Fruit drupaceous, one-celled, curved around a placental process. Seed solitary and curved; embryo with the cotyledons coiled up in a peripheral form. The woody matter is often closely compacted in wedges, separated by large medullary plates, giving the stem a peculiar aspect on a cross section. Menispermads are common in the tropical woods of Asia and America, and they climb among the trees to a great height. The plants of this order have narcotic and bitter properties; some of them are very poisonous. *Anamirta paniculata* yields the bitter narcotic fruit known in commerce as Cocculus indicus, and which has been sometimes illegally used to impart bitterness to malt liquor; *Jateorrhiza palmata* (*Cocculus palmatus*) supplies the bitter tonic root known as Calumba; *Cissampelos Pareira*, furnishes the tonic and diuretic root, known by the name of Pareira brava.

Nat. Ord. 7.—Lardizabalaceae, the Lardizabala order.—Twining shrubs, with alternate exstipulate leaves, ternary symmetry and unisexual flowers, resembling Menispermads, but differing in their compound leaves, ovules sunk on the inner surface of the ovary, and minute embryo in abundant solid albumen. They are found in the cooler parts of South America and China.

Nat. Ord. 8.—Berberidaceae, the Barberry order (Fig. 431).—Shrubs or herbaceous perennial plants, with alternate compound leaves, which are often spiny from non-development of the parenchyma. Sepals, three, four, or six, deciduous, in a double row. Petals equal to the sepals in number, and opposite to them, or twice as many. Stamens equal in number to the petals, and opposite to them, anthers with two cells, each opening by a recurved valve from below upwards (Figs. 257 and 261). Carpel solitary, one-celled; stigma orbicular. Fruit baccate or capsular. Seeds anatropous; albumen fleshy and horny (Fig. 57). They are found in temperate parts of the northern and southern hemispheres. In their properties they are acid, bitter, and astringent. The fruit of *Berberis vulgaris*, the common Barberry, contains oxalic acid, and is used as a preserve; while its bark and stem are astringent, and yield the bitter yellow crystaline matter Berberine.

Nat. Ord. 9.—Cabombaceae, the Cabomba or Water-shield order.—Aquatic plants with floating peltate leaves. Sepals and petals three or four, alternating. Stamens 6-36. Carpels distinct, two to eighteen. Seeds definite; embryo in a vitellus, outside abundant fleshy albumen. They are allied to Nymphaceae and Nelumbiaceae, and differ in their distinct carpels, definite ovules, abundant albumen, and nearly complete absence of a torus. They occur in America and New Holland.

Nat. Ord. 10.—Nymphaeaceae, the Water-Lily order (Figs. 432 to 434).—Aquatic herbs with large showy flowers, and cordate or peltate leaves arising from a prostrate rhizome, which is sunk in the mud. Sepals usually 4, persistent. Petals numerous, deciduous, inserted on a fleshy torus, and passing by a gradual transition out of the sepals into the stamens, which are numerous, have petaloid filaments, and are inserted into the torus (Fig. 432). Ovary surrounded by the torus, many-celled, many-seeded, with radiating stigmas. Fruit indehiscent, pulpy when ripe. Seeds anatropous, attached to spongy dissepiments; embryo small, in a vitellus, outside farinaceous albumen (Fig. 433). There are considerable differences of opinion as to the position of this order. The structure of the rhizome resembles that of Endogens. The Water-lilies chiefly inhabit quiet waters in the northern hemisphere; they are rare in the southern hemisphere. The order possesses bitter, astringent, and some say narcotic properties. The plants contain much starch in their rhizomes, which are used for food in the same way as potatoes. Their petioles have large air-tubes, as well as spiral fibres, which can be separated and used for wicks. *Victoria regia*, Victoria Water-lily (Fig. 434), is found in the still waters of the whole of the warm parts of Eastern South America. Its flowers, when expanded, are a foot and more in diameter. Its leaves vary from four to six or eight feet in diameter.

Nat. Ord. 11.—Nelumbiaceae, the Nelumbium or Water-Bean order (Fig. 435).—Aquatic herbs resembling Water-lilies, but differing in their large exalbuminous embryo, and their remarkably enlarged tabular torus, in the hollow of which the nuts are half buried, and finally become loose. Found in quiet waters of temperate and tropical regions in the southern hemi- sphere; very frequent in the East Indies. The plants of the order are remarkable for their large showy flowers and leaves. Their nuts are eatable.

Nat. Ord. 12.—Sarraceniaceae, the Water-Pitcher order.—Perennial herbs growing in bogs, with hollow pitcher-shaped or trumpet-shaped leaves (Fig. 139). Calyx usually consists of five persistent sepals. Petals five or 0. Stamens 0. Style often expanding at its summit into a large peltate plate, with a stigma beneath each of its five angles. Fruit, a 2-5-celled capsule with axile placentas, bearing numerous albuminous seeds. The pitchers formed by the petioles of the leaves contain a peculiar secretion, the use of which is unknown. Sarracenia receives the name of Sidesaddle flower, in allusion to its tubular leaves. The plants are found abundantly in North America. Heliamphora occurs in Guiana.

*Pl. CXII., Nat. Ord. 13.—Papaveraceae, the Poppy order (Figs. and CXIII., figs. 6-11.

436 to 438.)—Herbs with milky or coloured juice, and alternate exstipulate leaves (Fig. 121). Sepals two, rarely three, caducous (Fig. 208). Petals four (Fig. 437), rarely six, usually crumpled in aestivation. Stamens 8-24 or more. Fruit unicellular, siliquiform (pod-like), with 2-5 parietal placentas, or capsular (Fig. 309), with numerous placentas. Seeds numerous, with embryo in the midst of fleshy and oily albumen (Fig. 438). The order is chiefly confined to Europe. Narcotic properties characterize the order. Some of the plants yield an acrid juice. Papaver somniferum is the Opium Poppy, the unripe capsules of which yield a milky juice, which, when concrete, constitutes opium. The active principle of opium is the alkaloid called Morphia, which is combined with meconic acid. Turkey opium is that chiefly used in Britain.

Nat. Ord. 14.—Fumariaceae, the Fumitory order (Fig. 439 and Fig. 160).—Herbs with brittle stems, a watery juice, alternate, cut, exstipulate leaves, and irregular unsymmetrical flowers. Sepals two, deciduous. Petals four, cruciate, irregular, one or two of them often saccate or spurred, and the two inner frequently cohering at the apex, so as to include the anthers and stigma. Stamens either four and free, or six and diadelphous, each bundle being opposite the outer petals, and the central anther being two-celled, while the two outer are one-celled. Fruit, a round and indehiscent nut, or a one-celled and two-valved pod. Seeds crested, with a minute embryo and fleshy albumen. Fumeworts occur chiefly in temperate regions of the northern hemisphere. Some of them, as Diclytra spectabilis, are very showy. They possess very slight bitterness and acidity.

Nat. Ord. 15.—Cruciferae or Brassicaceae, the Cruciferae or Cabbage order (Figs. 440 and 441).—Herbaceous plants with alternate, exstipulate leaves, racemose or corymbose flowers, usually yellow or white, and an ebracteated inflorescence. Sepals four, deciduous. Petals four, cruciate (Fig. 441). Stamens tetradynamous (Fig. 177). Fruit, a silique

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Fig. 410. Diagram of a Cruciferous flower, with four imbricate sepals, four petals, six stamens, tetradynamous, the two short ones solitary and opposite the lateral sepals, the four long ones opposite the anteposterior petals. The ovary is superior, with two divisions, one right and left of the axis, separated by a replum, seeds attached by a funicle to each side of the placenta. The floral symmetry is quaternary, the four stamens, four petals, six stamens, and two of them, and the fruit bicarpellary by abortion of two of the carpels.

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Fig. 314), or silicula (Figs. 315, 316). Seeds exalbuminous (Fig. 334); embryo with the radicle folded on the cotyledons (Figs. 337, 338). The plants are generally distributed, but abound in cold and temperate regions, especially in Europe. The order has been divided into sections, according to the nature of the fruit and of the embryo. The following are the divisions founded on the nature of the fruit:—1. Siliqueose,—a silique, opening by valves (Fig. 307). 2. Siliculose, Latispicate,—a silicula, opening with two flat or convex valves, replum in the broadest diameter (Fig. 315). 3. Siliculose, Augustispicate,—a silicula with folded or keeled delhiscent valves, replum in narrow diameter (Fig. 316). 4. Nucuminate,—an indehiscent silicula, often one-celled, having no replum. 5. Septalute,—valves with transverse phragmata on their inside. 6. Lomentaceae,—a pod dividing transversely into single-seeded portions, the beak sometimes containing one or two seeds, while the true pod is abortive. The divisions founded on the nature of the embryo are:—1. Pleurohizese (Fig. 337),—cotyledons accumbent o =. 2. Notorhizese (Fig. 338),—cotyledons incumbent o =. 3. Orthoplocar,—cotyledons duplicature o =. 4. Spirolobese,—cotyledons twice folded o =. 5. Diplolebose,—cotyledons thrice folded o =. Crucifers are antiscorbutic and pungent, and occasionally acrid in their properties. None of them are poisonous. The order contains many of the culinary vegetables in constant use, such as Cabbage, Cauliflower, Turnip, Radish, Sea-kale, Cress, and Mustard. The plants have much nitrogen and sulphur in their composition. Many garden flowers, as Wallflower, Stock, Rocket, and Honesty, belong to this order.

Nat. Ord. 16.—Capparidaceae, the Caper order.—Herbs, shrubs, or trees with alternate leaves and tetramorous flowers; allied to Crucifers, but distinguished by the stamens being often indefinite, and if six, scarcely ever tetradynamous, by the want of a replum in the one-celled ovary, which is often supported on a gynophore, and by their reniform seeds. Capparids are chiefly tropical plants. In their properties, they resemble Crucifers. They have pungent, stimulant, antiscorbutic qualities. Capparis spinosa, in the southern parts of Europe, C. ruprestis in Greece, C. Fontanesii in Barbary, and C. aquatica in Egypt, supply Capers, which are the flower-buds of the plants.

Nat. Ord. 17.—Resedaceae, the Reseda or Mignonette order.—Herbaceous plants; rarely shrubs, with alternate leaves having minute glands at their base, and racemose or spiked inflorescence. Sepals 4-7, sometimes united. Petals 2-7, lacerated and unequal, with broad or thickened claws (Fig. 218). Stamens definite, inserted on a fleshy disk. Fruit usually one-celled, opening early at the apex, with Botany.

3-6 parietal placentas. Sometimes it appears as carpellary leaves surrounding a central placenta. Seeds several, reniform, or curved, and exalbuminous; embryo arcuate. The plants of the order chiefly inhabit Europe and the adjoining parts of Asia and Africa.

Nat. Ord. 18.—Flacourtiaceae or Bixaceae, the Arnotto order.—Shrubs or small trees, with alternate exstipulate leaves, often marked with round transparent dots. Sepals and petals 4-7, the latter sometimes 0. Stamens, same number as the petals or a multiple of them. Ovules attached to parietal placentas. Fruit one-celled, either fleshy and indehiscent, or a 4-5-valved capsule containing pulp, in which numerous albuminous seeds are enveloped. The plants are almost entirely natives of the hottest parts of the East and West Indies and of Africa. Some of the plants of the order are bitter and astringent, others yield edible fruits. *Bixa orellana* has angular seeds covered with an orange-red pulp, which constitutes Arnott, and is used for a red dye.

Nat. Ord. 19.—Cistaceae, the Rock-rose order (Figs. 442 and 443).—Shrubs or herbs, often viscid, with simple, entire leaves, and showy flowers. Sepals 3-5, persistent, unequal, the three inner with twisted aestivation. Petals five, very rarely three, caducous, often crumpled, twisted in an opposite direction from the sepals. Stamens definite or 0, distinct. Fruit a one-celled capsule with parietal placentas, or imperfectly 3-5-celled by means of dissepiments arising from the middle of the valves, and bearing placentas at or near the axis (dehiscence being loculicidal). Seeds usually orthotropical, with mealy albumen; embryo curved or spiral. The plants are found chiefly in the south of Europe and north of Africa. The Rock-roses are generally resinous and balsamic. *Cistus creticus*, and other species (*C. ladaniferus*, *C. Ladanum*), furnish the resinous substance called Ladanium, which is used as a stimulant and emmenagogue.

Nat. Ord. 20.—Violaceae, the Violet order (Figs. 444 and 445).—Herbs or shrubby plants, with usually alternate, stipulate leaves (Fig. 136 and 169), having an involute vernation, and flowers often irregular. Sepals five, persistent, attached above their base. Petals five, often unequal, one being spurred. Stamens five, with short and broad filaments, which are often elongated beyond the introrse anther lobes; in the irregular flowers two of the stamens have appendages (Fig. 262); anthers sometimes united. Style declinate, with an oblique hooded stigma (Fig. 289). Fruit a three-valved capsule, with parietal placentas in the middle of the valves (loculicidal). Seeds definite or 0, albuminous, anatropial, with a straight embryo. The species are found in Europe, America, Siberia, and Africa. The Violet-worts are generally emetic, and some have purgative properties. In the roots of many of them a principle called Violin, similar to Emetic, has been found.

Nat. Ord. 21.—Droseraceae, the Drosera or Sun-dew order.—Herbaceous marsh-plants, often covered with glandular hairs (Fig. 107); they have alternate leaves, with fringes at their base, and a circinate vernation. Sepals five, imbricate. Petals five, imbricate. Stamens as many as the petals, or two or three times as many, distinct, withering. Styles 3-5, sometimes united. Fruit a one-celled, 3-5-valved capsule, with loculicidal dehiscence. Seeds numerous; embryo small, in the base of fleshy albumen. The plants are found in marshy grounds in various parts of the world, and have acid and slightly acrid properties.

Nat. Ord. 22.—Polygalaceae, the Milkwort order (Fig. 446).—Herbs or shrubs with simple exstipulate leaves. Pedicels have three bracts, and the flowers are irregular, unsymmetrical, and falsely papilionaceous. Sepals five, irregular, odd one posterior, two inner ones (wings) usually petaloid. Petals more or less united, usually three, of which one (the keel) is anterior, larger, and sometimes crested. Stamens 6-8, usually combined into a tube which is split on the upper side; anthers one-celled, opening by pores. Ovary usually two-celled, with a single pendulous, anatropal ovule in each cell; style curved. Capsule flattened with albuminous, carunculate seeds, containing a straight embryo. The order is considered by St Hilaire and others as allied to Sapindaceae, and some authors place it near Leguminosae, from which it differs in its hypogynous stamens, and in the odd sepal being superior and the odd petal inferior. The plants are scattered over various quarters of the globe. They are generally bitter and acrid, and their roots yield a milky juice. *Polygala Senega*, Snake-root, is a North American species, the root of which is used as an emetic, cathartic, and salagogue.

Nat. Ord. 23.—Krameriaceae, the Rhatany order.—The genus *Krameria* is the only one in this order which differs from Polygalaceae in the want of the falsely papilionaceous flowers, in its simple one-celled ovary, and in the absence of albumen. *Krameria triandra*, which yields the Rhatany-root, is a native of South America. The root is very astringent.

Nat. Ord. 24.—Tremandraceae, the Porwort order.—The plants of this order are slender, heath-like shrubs, with hairs usually glandular. They are allied to Polygalaceae, and differ in their regular symmetrical flowers, valvate calyx, and hooked appendages at the apex of their seeds. They are found in New Holland.

Nat. Ord. 25.—Tamaricaceae, the Tamarisk order.—Shrubs or herbs usually growing by the sea-side, with entire, scale-like leaves, and spiked or racemose flowers. Calyx 4-5-parted, persistent. Petals 4-5, withering, imbricate. Stamens 4-5, twice that number, free or united; anthers introrse, opening longitudinally. Styles three. Fruit, a three-valved, one-celled capsule, with three basal or parietal placentas, bearing numerous anatropal, comose, exalbuminous seeds. Embryo straight. The species abound in the basin of the Mediterranean, and are confined to the northern hemisphere of the Old World. They have an astringent, and slightly bitter and tonic bark.

Nat. Ord. 26.—Frankeniaceae, the Frankenia order.— Herbs or undershrubs, with opposite exstipulate leaves, and flowers embosomed in leaves. They are allied to Caryophyllaceae, and differ in their parietal placentation, and straight embryo. They have a tubular furrowed calyx, and long-clawed petals with appendicular scales. They occur chiefly in the north of Africa and south of Europe. Their properties are mucilaginous.

Nat. Ord. 27.—Elatinaceae, the Elatine or Water-pepper order.—Small annuals growing in marshes, with opposite leaves, interpretibulary membranaceous stipules, and minute axillary flowers. Sepals and petals 3-5. Stamens as many, or twice as many as the petals, distinct. Fruit a 3-5-celled septicidal capsule. Seeds numerous, attached to a central placenta, exalbuminous; embryo straight. The order is perhaps allied to Rutaceae, in which alliance it is placed by Lindley. The plants are found in all quarters of the globe. Their properties are said to be acid; hence the English name of the order.

Nat. Ord. 28.—Caryophyllaceae, the Clovewort order (Figs. 447 to 449).—Herbaceous plants with stems tumid at the articulations, entire, opposite leaves, and cymose inflorescence (Fig. 168). Sepals 4-5, distinct or united (Fig. 203). Petals 4-5 (Fig. 448), unguiculate, sometimes 0. Stamens as many, or twice as many as the petals, sometimes fewer. Ovary often supported on a gynophore, usually one-celled, with a free central placenta (Fig. 449). Styles 2-5, papillose on their inner surface. Fruit a capsule opening by 2-5 valves, or by teeth at the apex (Fig. 308), which are twice as many as the stigmas. Seeds usually indefinite; embryo curved round mealy albumen (Fig. 336). The various species of Pink (Dianthus), and Chickweed (Stellaria), are included in this order. The plants are found principally in temperate and cold regions.

Nat. Ord. 29.—Vivianiaceae, the Viviana order.—Herbaceous or suffruticose plants, with opposite or whorled exstipulate leaves and regular flowers in corymbose cymes. They are characterized by a ten-ribbed valvate calyx, a marcescent corolla, ten free stamens, a three-celled loculicidal capsule, and albuminous seeds, with a curved embryo. They are found in South America.

*P.CXIV. Nat. Ord. 30.—Malvaceae, the Mallow order* (Figs. 450 and 451).—Herbs, shrubs, or trees, with alternate, stipulate, palmately-divided leaves, often stellate hairs, and showy involucrate flowers on axillary peduncles (Fig. 172). Sepals five, rarely three or four, united at the base, valvate, often having an epicalyx. Petals of the same number as the sepals, twisted. Stamens 50, monadelphous (Fig. 451), united to the claws of the petals; anthers one-celled, reniform, introrse, opening transversely (Fig. 249); pollen hispid (Fig. 266). Ovary many-celled, with placentas in the axis; or several ovaries, separate or separable when ripe; styles equal in number to the carpels, distinct or united. Fruit composed of several monospermal or poly-spermal carpels, either combined or separate. Seeds with little albumen; embryo curved with folded cotyledons. The plants abound in tropical regions, and in the hotter parts of the temperate zone. The properties of the Mallowworts are mucilaginous and demulcent. They supply various kinds of fibres. *Althaea officinalis*, Marsh Mallow, is used medicinally to supply mucilage. Various species of *Gossypium* furnish cotton, which consists of the hairs attached to the seeds. These hairs are usually hollow cells, but occasionally they become flattened. There are probably four distinct species of plants furnishing the Cotton of commerce—1. *Gossypium herbaceum*, the common Cotton plant of India, a variety of which supplies the Chinese or Nankin Cotton. 2. *G. arboreum*, the Tree-Cotton of India. 3. *G. barbadense*, Barbadoes Cotton, called in India Bourbon Cotton; this supplies the highly-esteemed Sea Island Cotton. 4. *G. peruvianum* of Cavanilles, or *G. acuminatum*, which supplies the Pernambuco or Brazil Cotton. The inner bark of *Hibiscus cannabinus* furnishes a kind of Sun-hemp in India.

Nat. Ord. 31.—Sterculiaceae, the Silk-cotton order.—Large trees or shrubs, with simple or compound leaves, and occasionally unisexual flowers, resembling the Malvaceae in their general characters, particularly in their columnar stamens, but differing in their two-celled extrorse anthers. They are tropical plants. The Sterculiads resemble the Malvacées in their properties. *Adansonia digitata*, the Baobab tree, Monkey-bread or Ethiopian Sour-gourd, is one of the largest trees in the world, its trunk attaining a diameter of 30 feet. *Bombax Ceiba*, the Silk Cotton-tree, has a cottony matter surrounding its seeds, which is used for stuffing cushions and other domestic purposes. *Durio zibethinus*, the Durian, yields an edible fruit with a civet-like odour.

Nat. Ord. 32.—Bignoniaceae, the Chocolate order (Fig. 452).—Trees, shrubs, and undershrubs, with simple leaves, resembling the Sterculiaceae and Malvaceae, but differing from the former in their introrse anthers, slightly monadelphous, and often partially sterile stamens; and from the latter in their usually definite not columnar stamens, two-celled anthers, and smooth pollen. The fruit is a capsule com- posed of a few carpels. They are chiefly tropical or subtropical plants. In their properties Butternuts resemble Malvaceae. *Theobroma Cacao*, the Cacao-tree (Fig. 452), is a small tree which abounds in the forests of Demerara. From the seeds called Cacao-beans, the substances called Cocoa and Chocolate are prepared.

Nat. Ord. 33. **Tiliaceae**, the Linden order.—Trees or shrubs with alternate leaves having deciduous stipules (Fig. 105), floral envelopes tetramerous or pentamerous, calyx valvate, stamens *c*, outer ones sometimes petaloid and abortive, anthers two-celled, a glandular disk, style one, fruit dry or pulpy with several cells, often by abortion once-celled, seeds anatropous and albuminous. They are chiefly tropical plants. In northern temperate regions some form timber-trees. The plants of the order possess mucilaginous qualities. Many of them yield timber, fibres, and edible fruits. *Corchorus capsularis* yields the textile material called Jute, or Jute Hemp. *Tilia europaea*, the Lime or Linden tree, has a fibrous endodermis, which furnishes the Bass or Bast employed in the manufacture of Russian mats.

Nat. Ord. 34.—**Dipterocarpaceae** or **Dipterocarpaceae**, the Sumatra-Camphor order.—Large trees with resinous juice, alternate, involute leaves, convolute stipules; long wing-like, imbricate, unequal, calyx lobes; contorted petals; indefinite, distinct, or polyadelphous stamens, subulate anthers; coriaceous, one-celled fruit, surrounded by the calyx, the enlarged divisions of which form winged appendages; single, exalbuminous seed. Tropical Indian trees. The plants of this order yield a resinous balsamic juice which assumes various forms. *Dryobalanops Camphora* or *aromatica*, supplies the hard Camphor of Sumatra, and a resinous oily fluid called the liquid Camphor, or Camphor-oil of Borneo. The wood of *Shorea robusta* is much used in India under the name of Sál. *Vateria indica* furnishes the Piney Resin of India.

Nat. Ord. 35.—**Chilenaceae**, the Leptolena order.—Trees or shrubs with alternate, feather-veined, entire leaves, convolute stipules, involucrate flowers, which have three imbricate sepals, five convolute petals, numerous stamens, often monadelphous, a three-celled ovary, a capsular fruit, and albuminous seeds. They are found in Madagascar.

Nat. Ord. 36.—**Teeniosthiaceae**, the Tea order (Figs. 453 and 454).—Trees or shrubs with alternate coriaceous, usually exstipulate, and entire leaves, showy and generally unsymmetrical flowers. Sepals 5-7, with imbricate aestivation. Petals 5, 6, or 9, often combined at the base. Stamens *c*, distinct or united. Fruit a 2-7-celled capsule, usually with a central column. Seeds large, very few, with or without albumen. They are ornamental plants, found chiefly in Tropical America and in Eastern Asia. Those cultivated in Britain are principally from North America and China. The plants of the order have stimulating and slightly narcotic properties. Numerous varieties of *Camellia japonica* are cultivated, which are highly esteemed by florists. *Thea* is the genus which includes the various species and varieties of Tea. According to Fortune, there are two species of Tea, *Thea Bokhea* (Fig. 453), and *Thea viridis* (Fig. 454), from each of which Black and Green Tea is manufactured. The latter species is that which supplies the Tea sent from China to Britain. The difference in the appearance and quality of Teas depends partly on the climate and species, but chiefly on the time of gathering, and the mode of manufacture. The young leaves, quickly dried and subjected to a particular kind of manipulation, supply the Green Tea, while the older leaves dried more slowly, and after undergoing a process of fermentation, constitute the Black Tea. In some instances Tea is dyed of a green colour by means of a mixture of Turmeric, Prussian Blue, and Gypsum.

Nat. Ord. 37.—**Olacaceae**, the Olax order.—Trees or shrubs, often spiny, with alternate, exstipulate leaves, a cup-shaped calyx, being enlarged with the fruit and often covering it, five valvate petals, 5-10 stamens, partly sterile, five fertile ones being opposite the petals, a disk, a succulent fruit with a hard endocarp, and an albuminous seed without integuments (exutive). An order of mostly tropical shrubs, containing few species. Some yield edible fruits.

Nat. Ord. 38.—**Icacinaceae**, the Icaina order.—Evergreen trees and shrubs allied to Olacaceae, but differing in the calyx not enlarging with the fruit, stamens being alternate with the petals, ovary plurilocular, with axile placentation, and seeds having the usual integuments (indutive). The order is chiefly tropical.

Nat. Ord. 39.—**Cyriillaceae**, the Cyrella order. Evergreen shrubs with exstipulate leaves, allied to Olacaceae and differing chiefly in their imbricate not valvate petals, which are not hairy. They are found in North America.

Nat. Ord. 40.—**Aurantiaceae**, the Orange order (Figs. 455 and 456). Trees or shrubs with alternate, compound, exstipulate, dotted leaves (Fig. 133), and fragrant flowers. Calyx short, urceolate or campanulate, 3-5-toothed. Petals, 3-5. Stamens equal in number to the petals, or a multiple of them, inserted along with the petals on a hypogynous disk (Fig. 456); filaments sometimes united in one or more bundles. Ovary free; style cylindrical; stigma thickish. Fruit a hesperidium, sometimes, as in fingered Citrons and horned Oranges becoming monstrous by the separation of the carpels, or by the multiplication of carpels, so that one fruit is included within another. Seeds exalbuminous, often polyembryonous. Chiefly East Indian plants. The leaves and the rind of the fruit contain a volatile fragrant oil, and the pulp of the fruit is more or less acid. *Egle Marmelos*, the Indian Bael or Bela, yields a delicious fruit; its root and bark are antispasmodic; the decoction and jelly of the fruit are used in diarrhoea. *Citrus Aurantium*, the Sweet Orange, has been so generally distributed over different quarters of the globe, that its native country can scarcely be Botany. It has been naturalized in Europe. The rind of the fruit yields an oil called Oil of Orange, while the flowers supply another kind of oil. The pulp of the fruit contains malic acid. *C. vulgaris* (*C. Bigaradia* of some authors), the Bitter or Seville Orange, is probably a variety. It differs from the Sweet Orange in the larger wing of its petiole, its more fragrant flowers, its darker fruit, and its more bitter rind and pulp. In the young state, the fruit is known as Orangettes or Curacao Oranges. The flowers yield an essential oil called Neroli oil. The distilled water of the flowers has hypnotic qualities. *C. Limonum*, the Lemon, yields an acid antiscorbutic juice. It contains citric acid. *C. Limetta* produces the Lime, and var. *Bergamia*, the Bergamot; *C. medica* is the source of the Citron; *C. Decumana* furnishes the Shaddock; *C. paradisi* the forbidden fruit; *C. Pomellosus* the Pompelmoose; and *C. japonica*, the Kumquat of China.

Nat. Ord. 41.—**Hypericaceae**, the St John’s Wort order (Fig. 457).—Herbs, shrubs, or trees, with a resinous juice, regular flowers, opposite, entire, exstipulate leaves, usually with transparent dots and blackish glands. Sepals 4-5, persistent, two outer often smaller. Petals 4-5, unequal-sided, twisted in restivation, often bordered with black dots. Stamens generally $\alpha$ and polyadelpous. Carpels 3-5 partially united. Fruit a capsule with septicidal dehiscence. Seeds numerous and exalbuminous. The order is generally distributed both in warm and temperate regions. There are 280 known species. The properties of the plants are usually purgative; some are tonic and astringent. Many species of *Hypericum* yield a yellow juice and an essential oil. Species of *Viscum* yield a gum-resin like Gamboge.

Nat. Ord. 42.—**Guttiferae** of Clusiaceae, the Gamboge order.—Trees or shrubs with a resinous juice, opposite coriaceous entire leaves, and occasionally unisexual flowers. Sepals and petals 2, 4, 5, 6, or 8, the former often unequal, the latter equilateral. Stamens numerous, often united. Disk fleshy. Ovary one or many-celled; stigma usually sessile and radiate. Fruit dry or succulent, one or many-celled. Seeds exalbuminous, often immersed in pulp. Natives of humid and hot places in tropical regions, chiefly South America. The properties of the order are in general acrid and purgative. The plants yield a yellow gum resin. *Cambogia Gutta* (*Hebadorendron cambogoides* of Graham) is the source of Ceylon Gamboge. Different species of *Garcinia* yield a substance like Gamboge. *Garcinia cochinchinensis* has been said to be the source of the Siam Gamboge, the best commercial specimens of which are in the form of pipe Gamboge, but this is very doubtful. *Garcinia elliptica*, found in Syllot and Tavoy, also supplies a kind of Gamboge. Coorg or Wynaad Gamboge is also the produce of a Garcinia, perhaps *G. pictoria*. Gamboge is used as a pigment and as a drastic purgative. *Garcinia Mangostana*, a native of Malacca, produces the Mangosteen, one of the finest known fruits. *Mammee americana* produces the Mammee Apple.

Nat. Ord. 43.—**Marcgraviaceae**, the Marcgravia order.—Trees or shrubs allied to Guttiferae, and differing chiefly in their alternate leaves, unsymmetrical flowers, and versatile anthers. Some of the plants have remarkable pitcher-like bracts. They are found in equinoctial America chiefly.

Nat. Ord. 44.—**Hippocrateaceae**, the Hippocratea order.—Shrubby plants with opposite simple leaves having deciduous stipules. Sepals and petals 5, imbricate. Stamens three, monadelphous. Fruit either consisting of three winged carpels or baccate. Brown and Lindley put the order near Celastraceae, notwithstanding its hypogynous stamens. They are principally South American plants; some occur in Africa and India. The nuts of *Hippocretia comosa* are oily and sweet. The fruit of *Tontelea pyriflora* is eaten in Sierra Leone.

Nat. Ord. 45.—**Malpighiaceae**, the Malpighia order.—Trees or shrubs, often climbing, with opposite or alternate leaves, and short deciduous, sometimes intrapetiolate, stipules; occasionally showing peltate hairs. Sepals five, combined at the base, glandular. Petals five, unguiculate. Stamens ten, often monadelphous. Ovary generally of three carpels. Fruit a drupe, a woody nut, or a samara. Seed orthotrop, suspended by a cord, exalbuminous, embryo straight or curved. Malpighiads are nearly all tropical plants. Their properties are generally astringent. Many are handsome trees or climbers with showy flowers. The wood is sometimes formed in an anomalous manner (Fig. 81).

Nat. Ord. 46.—**Erythroxylaceae**, the Erythroxylon order.—Allied to Malpighiads, and distinguished by the flowers growing from among imbricated scales, the absence of calyxine glands, the presence of plaited scales at the base of the petals, and by the ovules being anatropal and cordless. They are West Indian and South American plants. Some of them have stimulating qualities, others yield a tonic bark. *Erythroxylon Coca*, a Peruvian plant, called Ipádi by the Indians of the Rio Negro, is famed for exciting the nervous system.

Nat. Ord. 47.—**Aceraceae**, the Maple order.—Trees with opposite, simple, often palmate, exstipulate leaves, and corymbose or racemose unsymmetrical flowers. Calyx usually of five parts. Petals as many as the sepals, or none. Stamens generally eight, inserted on or around a hypogynous disk. Ovary of two carpels, more or less united; ovules in pairs. Fruit samaroid. Seed solitary, exalbuminous; embryo coiled. Found in the temperate parts of Europe, Asia, and America. Their properties are saccharine, the trees yield light and useful timber. *Acer Pseudoplatanus* is the Common Sycamore or Greater Maple, which thrives well even when exposed to the sea. *A. saccharinum*, the Sugar-Maple, supplies the maple sugar of America.

Nat. Ord. 48.—**Sapindaceae**, the Soapwort order.—Trees, shrubs, or climbers with tendrils, rarely herbs; having alternate or opposite, usually compound leaves, and unsymmetrical, generally irregular and polygamous flowers. Calyx with 4-5 sepals. Petals 4-5, occasionally 0, sometimes with an appendage inside. Disk fleshy. Stamens usually 8-10. Ovary 2-3-celled; style undivided, or 2-3-cleft. Fruit capsular or fleshy, sometimes winged. Seeds exalbuminous, arillate; embryo usually curved. Found chiefly in the tropical parts of South America and India. The *Hippocastanum* or Horse-chestnuts, distinguished by opposite leaves (Fig. 131), and two ovules in each cell, one erect, and the other suspended, occur in the north of India, Persia, and the United States. The properties are various. Many of the plants have saponaceous qualities, hence the name of the order. Some are astringent; others yield edible fruits and seeds, and not a few are poisonous. The bark of *Aesculus Hippocastanum*, the Horse-chestnut, is febrifugal. *Cupania (Blightia) sepida*, furnishes the Aloe fruit, with its remarkable succulent edible arillus. *Nepheleum (Euphoria) Litchi*, supplies the Li-chi fruit of China. *Ophiocaryon paradoxum* is the Snake-nut-tree of Demerara. *Paulinia sorbilis* is the Guaráná plant, the seeds of which supply an important tonic beverage in Brazil.

Nat. Ord. 49.—**Rhizobolaceae**, the Suarrow-nut order.—Trees with opposite, digitate, exstipulate leaves. Sepals 5-6, more or less combined. Petals 5-8, unequal. Stamens $\alpha$, arising with the petals from a hypogynous disk. Fruit of several combined indehiscent, one-seeded nuts. Seed reniform, exalbunious, with a cord dilated into a spongy excrescence; radicle very large. Found in South America. The plants of the order are large timber trees, some of which yield edible fruit. *Caryocar butyraceum* (*Pekoa tuberculosa*) is a gigantic tree of Demerara, producing the Souari, Suarrow, or Surahwa nuts, the kernels of which are esteemed the most agreeable of all the nut kind.

Nat. Ord. 50.—**Meliaceae**, the Melia order.—Trees or shrubs with alternate, exstipulate, simple or compound leaves. Sepals 3, 4, or 5, more or less united. Petals, the same number. Stamens twice as many as the petals. Disk, cuplike. Ovary, with cells varying from 3 to 12. Fruit succulent or capsular. Seeds not winged, with or without albumen; embryo with leafy cotyledons. They are chiefly tropical plants, and are found in Asia, America, and Africa. The properties of the order are bitter, astringent, and tonic. Some of the plants act as powerful purgatives and emetics. *Melia Azedarachta*, the Neem-tree or Pride of India, has febrifugal qualities. The pericarp yields an oil used for lamps.

Nat. Ord. 51.—**Humiriaceae**, the Humirium order.—Balsamic trees or shrubs, with alternate, simple, exstipulate leaves. Calyx in five divisions. Petals five, imbricate. Stamens 5, monadelphous; anthers two-celled, with a membranous connective beyond the lobes. Disk often present. Ovary five-celled. Fruit a drupe. Seed albuminous; embryo orthotropial. Natives of tropical America. The Balsam of Umiri is procured from *Humirium floribundum*, by making incisions into its trunk.

Nat. Ord. 52.—**Cedrelaceae**, the Mahogany order.—Trees with alternate, pinnate, exstipulate leaves, allied to Meliaceae, and chiefly distinguished by their indefinite and winged seeds. The fruit is capsular, the valves separating from a thick axis. They are common in the tropical parts of America and India. The properties of the order are fragrant, aromatic, and tonic. Many yield timber. *Cedrela febrifuga* has a febrifugal bark. *Soyoida febrifuga*, the Red-wood tree, is febrifugal and astringent. *Swietenia Mahagoni*, the Mahogany, grows in dense forests, and forms one of the most lofty and gigantic tropical trees.

Nat. Ord. 53.—**Vitaceae** or Ampelideae, the Vine order

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**Fig. 458.**

The Vine (*Vitis vinifera*), showing the leaves with radiating venation, the clusters of flowers, and the tendrils or cirri, coiled up in a spiral form.

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(Fig. 458).—Shrubby plants climbing by tendrils, with tumid joints, simple or compound leaves, opposite below, alternate above, and small green flowers arranged in a racemose or umbellate manner. Calyx small, nearly entire. Petals 4-5, induplicate, inserted outside a disk, sometimes clustering at their tips, and caducous (Fig. 218). Stamens 4-5, opposite the petals, inserted on the disk (Fig. 238). Ovary usually two-celled, with two erect ovules in each cell. Fruit a uva. Seeds with a bony spermometer; embryo small in horny albumen. The tendrils in this order are abortive branches (Fig. 72). Vineworts inhabit the milder and hotter regions of the globe. They are common in the East Indies. The Grape Vine (*Vitis vinifera*) is said to be a native of the shores of the Caspian, whence it has been widely distributed. The plants of this order have acid leaves and a pulpy fruit more or less acid at first, but developing grape-sugar as it ripens. They have frequently large dotted vessels abounding in sap, and they bleed copiously. Spiral vessels with air are common in the Vine.

Nat. Ord. 54.—**Geraniaceae**, the Cranesbill order (Fig. 459).—Herbs or shrubs, with tumid joints, opposite or alternate leaves, usually palmately-veined and lobed, often stipulate. Sepals 5, imbricate, one sometimes spurred. Petals 5, unguiculate, contorted in aestivation. Stamens usually 10, monadelphous, occasionally some sterile. Ovary of five bi-ovular carpels placed round an elongated axis to which the styles adhere. Fruit formed of five one-seeded carpels, which finally separate from the base of the central axis or beak, and curve upwards by means of the attached styles (Fig. 183); the fruit is said to be gynobasic, and the long beak or carpophore gives origin to the name of the order. Seed exalbunious; embryo curved and doubled up, with plaited cotyledons. Distributed over various parts of the world. The species of *Pelargonium* abound at the Cape of Good Hope. The order has astringent and aromatic properties. Many of the plants are fragrant. Some have a musky odour.

Nat. Ord. 55.—**Linaceae**, the Flax order (Fig. 460).—Herbs with entire, sessile, alternate or opposite or verticillate leaves, which are exstipulate or have occasionally a pair of minute glands at their base. Flowers regular and symmetrical. Sepals 3-5, imbricate. Petals 3-5, contorted in aestivation. Stamens united at the base, 3-5, usually with intermediate abortive ones in the form of teeth opposite the petals. Ovary 3-5-celled; styles 3-5 (Fig. 275). Fruit a plurilocular capsule, in which the cells are more or less completely divided into two by spurious divisions proceeding from the dorsal sutures. Seeds, one in each cell, anatropial, with little or no albumen; embryo straight, cotyledons flat. Distributed over various quarters of the globe, but most abundant in Europe and the north of Africa. The order is distinguished by its mucilaginous properties, and by yielding valuable fibres. Some species are purgative and diuretic. *Linum catharticum*, called Purging-flax, fig. CXXV. from its properties. *L. usitatissimum*, the cultivated Flax, fig. 1, yields tenacious fibres, used in the manufacture of linen. Its seeds are demulcent and oily.

Nat. Ord. 56.—**Oxalidaceae**, the Wood-sorrel order (Fig. 461).—Herbaceous or shrubby plants with alternate, rarely opposite, simple or compound leaves, and regular... Botany. Sepals five, imbricate. Petals five, twisted. Stamens ten, more or less monadelphous, of different lengths. Fruit usually a five-celled capsule, sometimes drupaceous. Seeds with a fleshy outer coat, which bursts in an elastic manner when ripe, so as to expel the seeds; embryo straight and large in thin albumen. The plants are allied to Geraniaceae, and differ chiefly in their gynoecium. The plants of the order are met with both in hot and in temperate regions. They are very common in America and at the Cape of Good Hope. The shrubby species are confined to warm climates. The Oxalids or Wood-sorrels have generally acid properties, from the presence of oxalic acid in the form of binoxalate of Potass, which is called the salt of sorrel. Some of them have sensitive leaves. *Acerroba Bilimbii*, the Blimbing of the East Indies, has an acid fruit, which is used as a pickle. *Oxalis crenata* bears tubers which are used as potatoes. *O. Deppei* has fleshy roots, which are used as culinary vegetables.

Nat. Ord. 57.—BALSAMINACEAE, the Balsam order (Fig. 462).—Annual succulent herbs, with simple, exstipulate leaves, and irregular flowers. Sepals five, coloured, irregular, the odd one spurred. Petals five, irregular, distinct or cohering. Stamens five. Ovary of five united carpels; stigmas sessile. Fruit, a capsule opening septifragally by five elastic valves, which become coiled up (Fig. 462). Seeds exalbuminous; embryo straight. The flowers are usually showy. The ripe capsules burst elastically when touched, so as to scatter the seeds; hence the name of *Impatiens noli-me-tangere* given to one of the species. The plants abound in India.

Nat. Ord. 58.—TROPICAOLACEAE, the Indian Cress, or Nasturtium order (Fig. 463).—Trailing or twining herbs, with alternate, exstipulate, and peltate or palmate leaves. Calyx spurred, formed by five united sepals. Petals five, the two upper arising from the throat of the calyx, remote from the three lower unguiculate petals. Stamens usually eight, distinct. Ovary of three united, one-seeded, carpels. Fruit indehiscent, monospermal, carpidia separating from a common axis. Seeds exalbuminous, filling the cells; embryo large. They are chiefly South American plants. The properties of the order are acridity and pungency, resembling in this respect some of the Cruciferae. *Tropaeolum majus* is the common Indian Cress, or garden Nasturtium, the urine fruit of which is pickled, and used as a substitute for Capers. The roots of *T. tuberosum* are eaten in Peru.

Nat. Ord. 59.—LINNANTHACEAE, the Linnanthes order.—The plants of this order differ from Tropicaolaceae in their regular flowers, their erect ovules, and in the tendency to adhesion between the stamens and the calyx. Probably the order should be placed among Perigynous Exogens. It contains a few North American species, which have properties similar to Indian Cresses.

Nat. Ord. 60.—PITTOSPORACEAE, the Pittosporum order.—Trees or shrubs, with alternate, simple, exstipulate leaves. Sepals and petals, 4-5, distinct, or slightly cohering. Stamens five; anthers often porose. Ovary 2-5-celled; style one. Fruit, a capsule or berry. Seeds numerous, anatropal, often covered with a resinous pulp; embryo minute, in fleshy albumen. New Holland plants chiefly. They have more or less resinous qualities. The berries of some *Billardieras* are eatable. In *Cheiranthera linearis* the anthers are thrown to one side, and have a hand-like aspect.

Nat. Ord. 61.—BREXIAEAE, the Brexia order.—Trees, with alternate, simple, stipulate leaves, and green flowers in axillary umbels. Calyx five-parted. Petals five, contorted. Stamens five, arising from a narrow cup, with teeth between them. Style one. Fruit drupaceous, five-cornered, five-celled, rough. Seeds numerous, albuminous. Madagascar plants, of which little is known.

Nat. Ord. 62.—ZYGOPHYLLACEAE, the Bean-caper and Guaiacum order (Fig. 464).—Herbs, shrubs, or trees, with opposite, stipulate, usually pinnate, not dotted leaves. Calyx 4-5-parted, convolute. Petals unguiculate, at first minute, afterwards large, imbricate. Stamens 8-10, often arising from the back of scales. Ovary 4-5-celled, surrounded by glands or a disk; style simple. Fruit usually a capsule, 4-5-angled, opening in a loculicidal manner by 4-5 valves. Seeds usually albuminous (*Tribulas* is exalbuminous); embryo green. Bean-capers are generally distributed. Some are peculiar to America; others are found in Europe, India, Africa, and New Holland. The plants have diaphoretic and anthelmintic properties. The wood of the arborescent plants of the order is very hard and durable. *Guaiacum officinale* (*Lignum Vitae*), a West Indian tree, supplies the resin called Guaiac, which exudes from it spontaneously and after incisions. The resin and the wood are stimulant and diaphoretic. *Zygophyllum Fabago*, Bean-caper, is so called on account of its flower-buds being used as substitutes for Capers.

Nat. Ord. 63.—RUTACEAE, the Rue order (Figs 465 and 466).—Herbs, shrubs, and trees, with exstipulate dotted leaves and perfect flowers. Calyx in 4-5 divisions. Petals 4-5, occasionally 0. Stamens, as many, or twice, or thrice as many, as the petals, placed outside a hypogynous disk. Ovary, sessile or stalked, 3-5-lobed; styles united, occasionally separated at the base. Fruit of several car- pels, either combined, or more or less distinct, often separating when ripe, and dehiscing by one or both sutures. Seeds, one or two in each carpel; the true Rutaceae (European plants) have albuminous seeds, while the Diosmee (from the Cape and New Holland) have exalbuminous seeds. The plants are found in Europe, Cape of Good Hope, New Holland, and America. The order is characterized by its peculiar penetrating odour. The plants are employed medicinally as antispasmodics, tonics, and febrifuges. The leaves of Correa alba are used in Australia for tea. Dictamnus Fraxinella, False Dittany, abounds in volatile oil. Diosmae are the Buchu or Buchu plants found at the Cape of Good Hope, which are remarkable for their overpowering and penetrating odour, owing to the presence of a yellowish volatile oil. Galipea officinalis furnishes a tonic, febrifugal bark called Angustura. Ruta graveolens, common Rue, has antispasmodic properties.

Nat. Ord. 64.—XANTHOCYLALES, the Prickly-Ash order.—Trees or shrubs, with exstipulate, dotted leaves, resembling the Rutaceae, and distinguished by their polygamous flowers. They are chiefly found in tropical America. They have pungent and aromatic qualities, and have been used medicinally as stimulants, salagogues, and tonics. They yield a volatile oil, and a bitter principle called Xanthociprine.

Nat. Ord. 65.—OCHINACEAE, the Ochna order.—A small group of undershrubs or trees allied to Rutaceae, and distinguished by their simple, dotted, stipulate leaves, and their enlarged fleshy gynobase or torus. They are found in the tropical parts of India, Africa, and America. The order is characterized by bitter, tonic properties. The plants want the aromatic qualities of the Rueworts.

Nat. Ord. 66.—SIMARUBACEAE, the Quassia order (Fig. 467).—Trees or shrubs, with alternate, exstipulate, dotted, usually compound leaves. Calyx in four or five divisions. Petals 4-5, imbricated. Stamens 8-10, arising from the back of hypogynous scales. Ovary 4-5-lobed, stipitate; style simple. Fruit, consisting of 4-5 drupes arranged around a common receptacle. Seeds, one in each drupe, pendulous, anatropial, exalbuminous. Natives chiefly of the tropical parts of India, America, and Africa. Bitterness prevails in this order, the plants being used as tonics. Picrasma (Picraena) excelsa, Bitterwood, is a large tree, the wood of which is the common Quassia of the shops. It is bitter and tonic, and is sometimes used as a substitute for hops. Quassia amara, (Fig. 467) the true Quassia plant, is a tall shrub found in Surinam, having pinnate leaves with winged petioles. Simaba Cedron is a tree of New Grenada, which has long been celebrated as an antidote to snake bites. The bark of the root of Simaruba amara or officinalis is used as a substitute for Quassia.

Note.—Apetalous species occur in the following Thalamitidal orders:—Ranunculaceae, Menispermaceae, Papaveraceae, Phacellanthaceae, Caryophyllaceae, Sterculiaceae, Byttneriaceae, Tiliaceae, Malpighiaceae, Geraniaceae, Rutaceae, Xanthoclylaeae. Some species belonging to the orders Anonaceae and Rutaceae are Gamopetalous.

SUB-CLASS II.—CALYCIFLORA.

1. Polypetalae, or Dialypetalae.

Nat. Ord. 67.—STACKHOUISACEAE, the Stackhousia order.—Herbs, occasionally shrubs, with simple, alternate, stipulate leaves. Calyx five-cleft, tube inflated. Petals five, arising from the top of the calycine tube, claws united. Stamens five, distinct, perigynous. Styles 3-5. Fruit of 3-5 monospermal, indehiscent carpels, with a central column. Seed anatropial, albuminous. The order contains a few New Holland plants.

Nat. Ord. 68.—CELASTRACEAE, the Spindle-tree order.—Shrubs or trees, with alternate, rarely opposite, simple, stipulate leaves. Sepals and petals 4-5, imbricate. Stamens 4-5, inserted on a large disk which surrounds the ovary. Fruit superior, 2-5-celled capsular or drupaceous. Seeds usually arillate, albuminous, with a large straight embryo. Chiefly natives of the warm parts of Europe, North America, and Asia; also of the Cape of Good Hope. The order is more or less acrid, and some of the plants yield oil. Catha edulis is the Kat or Khát of the Arabs, the leaves of which are stimulant. Celastrus scandens has a purgative and emetic bark. Euonymus europaeus, the common Spindle-tree, has a beautiful scarlet arilode.

Nat. Ord. 69.—STAPHYLEACEAE, the Bladder-nut order.—Shrubs allied to Spindle-trees, and distinguished by their compound leaves, with stipules and stipels, more or less separate carpels, and a bony spermoderma. Some consider them as having hypogynous stamens, and place them near Sapindaceae. They are scattered over the globe. They receive the name of Bladder-nut from the membranous inflated fruit of some species, such as Staphylea pinata. Their bark is often bitter, while their seeds are oily and acrid.

Nat. Ord. 70.—CHAILETTIACEAE, the Chailletia order.—Trees or shrubs with alternate stipulate leaves. Calyx 5-parted; vestiture induplicato-valvate. Petals five, alternate with the divisions of the calyx, sometimes united; stamens five, with glands at their base. Ovary superior, 2-3-celled; ovules two, pendulous. Fruit 1-3-celled, dry. Seeds solitary, exalbuminous. Natives of tropical America and Africa, and of the East Indies. Chailletia toxicaria has a poisonous fruit called Ratsbaine in Sierra Leone.

Nat. Ord. 71.—RHAMNACEAE, the Buckthorn order.—Shrubs or trees, often spinose, with simple, alternate leaves, and small flowers. Calyx 4-5-cleft, valvate. Petals 4-5, cucullate or convolute, inserted on the throat of the calyx, sometimes 0. Stamens 4-5, opposite the petals. Ovary sometimes adherent to the calycine tube, immersed in a fleshy disk; ovules solitary. Fruit a capsule, berry, or drupe. Seeds erect, albuminous, not arillate. Generally distributed. The properties of the order are usually acid and purgative. Some are bitter, tonic, and astringent; others yield dyes. The fruit of some is edible. Hovenia dulcis is remarkable for the enlargement of its peduncles, which become succulent, and are used as a fruit in China. Rhamnus, Buckthorn, is the type of the order. R. catharticus yields a cathartic fruit. Jujube paste is prepared from the fruit of Zizyphus Jujuba and vulgaris. Z. Lotus is the Lote-bush, the fruit of which is used by the Arabs.

Nat. Ord. 72.—ANACARDIACEAE, the Cashew order (Fig. 468).—Trees or shrubs, with alternate, exstipulate, dotted leaves, and small, sometimes unisexual, flowers. Sepals 3-5, united. Petals 3-5, imbricate. Stamens equal in number to the petals, and alternate with them, or twice as many or more, perigynous or attached to a disk. Ovary one-celled; styles and stigmas usually three; ovule solitary, with a long curved cord attached to a basal placenta. Fruit indehiscent, a nut or drupe. Seed exalbuminous; embryo curved. The order forms a part of the Terebinthaceae of Jussieu. Chiefly found in tropical America, Africa, and India. The plants abound in a resinous, or milky, acid, and poisonous juice, which often becomes black in drying. The fruit, however, in some cases is eatable. *Anacardium occidentale*, the Cashew-nut, has a fleshy edible peduncle supporting a nut, the kernel of which can be eaten, while the pericarp is acid. *Mangifera indica* produces the Mango, a highly valued tropical drupaceous fruit. *Pistacia Lentiscus* and *atlantica* yield the resin called Mastic. *P. Terebinthus*, the Terebinth-tree, is the source of Chian turpentine. *P. vera* produces the Pistachio nut. *Rhus Toxicodendron*, the Poison-oak, has been used as a remedy in paralysis. *R. Cotinus*, Venetian Sumach, often produces hairs in place of flower-stalks (Fig. 158), and is called the Wig-tree. Its wood is known as young fustic.

Nat. Ord. 73.—AMYRINACEAE, the Myrrh order.—Trees or shrubs, with alternate or opposite compound, occasionally stipulate and dotted leaves. Calyx 2-5-divided. Petals 3-5, valvate. Stamens twice as many as the petals. Ovary 1-5-celled, surrounded by an annular disk; ovules in pairs; placentas apicar. Fruit 1-5-celled, hard and dry; exocarp splitting into valves. Seeds anatrop, exalbunous. Some consider the order as allied to Lauriaceae. Natives of tropical India, Africa, and America. The order abounds in balsamic resin. Some of the plants are bitter, others poisonous. *Amuris hexandra* and *A. Plumieri* are two of the sources whence Elemi is procured. *Balsamodendron Myrrha*, or an allied species, appears to be the source of the Myrrh of commerce, which is an aromatic, bitter gum-resin, containing volatile oil. *Boswellia thurifera (serrata)* and *B. globra* supply Olibanum.

Nat. Ord. 74.—CONNARACEAE, the Connarus order.—Trees or shrubs with alternate, compound, dotless, and usually exstipulate leaves. Calyx 5-parted, imbricate. Petals 5, usually imbricate. Stamens 10, perigynous or hypogynous, opposite the petals, usually united. Carpel 1 or more; style terminal; ovules 2, orthotrop. Fruit follicular. Seeds with or without albumen, often arillate. Tropical American plants. The aril of some *Omphalobiums* is eaten, and Zebra-wood is furnished by *O. Lamberti*.

Nat. Ord. 75.—LEGUMINOSE or FABACEAE, the Leguminous order (Figs. 469 to 471).—Herbs, shrubs, or trees, with alternate, usually compound, stipulate leaves (Figs. 129, 130). Calyx 5-divided, hypogynous, odd segment inferior (anterior). Petals usually five, sometimes one or more abortive, papilionaceous (Figs. 221 and 222), or regular, odd petal (if any) superior (posterior). Stamens definite or indefinite, perigynous, rarely hypogynous, distinct or united in one or more bundles (Figs. 470). Ovary superior, one-celled, one or many-seeded, sometimes consisting of one carpel (Fig. 272), sometimes of two or five. Style and stigma simple. Fruit a legume (Fig. 274), or a drupe. Seeds with or without albumen; embryo with large cotyledons (Fig. 61). The order is a very extensive one, and the plants belonging to it are found in all parts of the world. They are most abundant in warm regions, and diminish on approaching the poles. Leguminous plants have been divided into three sub-orders—Sub-order 1. Papilionaceae, petals papilionaceous, imbricate, upper one exterior (Fig. 221). Sub-order 2. Cesalpineae, petals imbricated, upper one interior (Fig. 471). Sub-order 3. Mimoseae, petals valvate in restivation.

The properties of the order are very various. Some are nutritious, others tonic and astringent; others purgative, and some poisonous. The plants supply timber, fibres, gums, dyes, and various other economical articles. Among the plants of the order may be noticed Beans, Peas, Lentils, Kidney-beans, and Pulse of various kinds, Lupins, Clover, Lucerne, Medick, Saintfoin, Liquorice, Traganth, Indigo, Kino. The greater number are more or less nutritious or wholesome. There are, however, some poisonous plants, as *Coronilla varia*, the seeds and bark of Laburnum, the Calabar bean, and others. *Echignomene patulosa* supplies Indian Rice-paper, the Shola of India. *Astragalus gummifer*, *verus*, and other species, furnish Gum Tragacanth. *Butea frondosa*, the Dhak-tree or Pulas of India, yields a kind of Kino. *Glycyrrhiza glabra* supplies Liquorice-root. *Indigofera tinctoria*, and *I. cerculea*, supply the Indigo of commerce. The Legumes of *Mucuna pruriens* and *prurita*, Cowitch, are covered with irritating hairs, which are used mixed with syrup as a vermifuge. *Myrosporum peruvianum* yields the Balsam of Peru, and *M. tolucense* that of Ton. *Pterocarpus Marsupium*, an Indian tree, is the source of Malabar Kino. *Cesalpinia brasiliensis* furnishes the Brazil-wood. Divi-divi, or Libi-divi, is the twisted legumes of *C. coriaria*, which are used in tanning. Species of *Cassia*, such as *C. acutiflora*, *lanceolata*, *elongata*, and *obovata*, furnish the various kinds of Senna. *Ceratonia Siliqua*, the Algroba-bean or Carob-tree, has an edible legume, which is used as food for horses. Various species of *Copaliera* yield the West Indian and Brazilian Balsam of Copiva. *Hamatoxylon campechianum*, the Logwood-tree, is used as a dye. *Tamarindus indica*, the Tamarind-tree, contains in its pod a laxative pulp, which is a secretion from the endocarp. Various species of *Acacia*, such as *A. Ehrenbergii*, *tortilis*, *vera*, and *arabica*, yield Gum Arabic and Gum Senegal.

Nat. Ord. 76.—MORINGACEAE, the Moringa order.—This order is considered as allied to Leguminose; the plants differing chiefly in their peltaloid sepals; stamens arising from a perigynous disk, a pod-like capsular fruit with three valves, three parietal placentas, and loculicidal dehiscence, with the seeds buried in the substance of the valves. Trees with pinnate or tripinate leaves, found in the East Indies and in Arabia. The properties of the order are usually stimulant and pungent. Some species yield a fragrant oil. *Moringa pterygosperma*, Horse-radish tree, has winged seeds. Its root has the taste of Horse-radish, and its seeds are called Ben-nuts, supplying Ben-oil, used by perfumers and watchmakers.

Nat. Ord. 77.—Rosaceae, the Rose order (Figs. 472 to 474).—Trees, shrubs, or herbs, with alternate, usually stipulate leaves, and regular, rarely unisexual, flowers. Calyx 4-5-lobed, sometimes calyculate, fifth lobe posterior. Petals 5 (Fig. 220), Botany. rarely o. Stamens definite or indefinite. Disk lining the tube of the calyx, or surrounding its orifice. Ovaries solitary or several, one-celled, with one or few anatropal ovules. Styles lateral (Figs. 288, 473), or terminal. Fruit achenes (Fig. 474), drupes (Fig. 302), follicles (Fig. 273), or pomes (Fig. 325). Seeds one or more, exalbuminous, with a straight embryo having flat cotyledons. This order is generally distributed over the globe, but the species are most abundant in temperate climates, where they supply many important fruits. The following are the divisions of the order:—Sub-order 1. Chrysobalanaceæ, trees or shrubs, carpel solitary, cohering more or less to one side of the calyx, ovules two, erect, style basilar; fruit a drupe, stipules not united to the petiole. Ex. Chrysobalanus. Sub-order 2. Amygdalaceæ, or Drupeaceæ, trees or shrubs, with a deciduous calyx-tube, carpel solitary, free, style terminal, fruit a drupe, stipules not united to the petiole. Ex. Amygdalus, Prunus. Sub-order 3. Rosaceæ, herbs and shrubs, carpels not adhering to the tube of the calyx, styles terminal or lateral, fruit achenes or follicles, stipules united to the petiole. Under this sub-order there are four tribes:—Tribe 1. Spiraeideæ, fruit a whorl of follicles, not inclosed within the calcine tube (Fig. 273). Ex. Spiraea. Tribe 2. Potentillideæ (Dyadæce of some), calyx-tube short or nearly flat, not inclosing the fruit; fruit achenes or drupes (acini), five or more, upon a flat or convex receptacle (Fig. 474 and 184). Ex. Rubus, Fragaria, Potentilla. Tribe 3. Sanguisorbideæ, achenes 1-2, inclosed within the dry calyx-tube, petals often 0 (Fig. 473). Ex. Alchemilla. Tribe 4. Rosideæ, achenes numerous, inclosed within the fleshy calcine tube, which is contracted at the orifice (Fig. 185). Ex. Rosa. Sub-order 3. Pomeæ, trees or shrubs, carpels 1-5, adhering more or less to the tube of the calyx and to each other; fruit a pome; stipules not united to the petiole (Fig. 325). Ex. Pyrus.

Astringent properties are exhibited by the bark and root of most of the plants of the order. Prussic acid occurs in the sub-orders Amygdalaceæ and Pomeæ. Many of the plants supply edible fruits, such as the Apple, Pear, Quince, Medlar, Loquat, Plum, Cherry, Peach. Chrysobalanus Icaco, the Cocoa-plum, is a West Indian stone-fruit. Amygdalus communis, the Almond-tree, is a native of Asia and Barbary, and is cultivated extensively to the south of Europe. There are two varieties,—one producing sweet, and the other bitter almonds. The kernels of the former contain a fixed oil and emulsion, while those of the latter contain in addition a nitrogenous substance called Amygdalin, which, by combination with emulsion, produces a volatile oil and Prussic acid. Cerastium Leuropetraeum, Cherry-laurel, or common Bay-laurel, yields a hydrocyanated oil. Prunus communis is the source of the common Plum. Brayera anthelmintica, Cusso or Kousso, an Abyssinian plant, is used as a vermifuge. Rosa centifolia, the common Cabbage-rose, and its varieties R. damascena and R. moschata, yield a fragrant essential oil, called Attar of Roses, which is distilled from the petals.

Nat. Ord. 78.—Calycanthiaceæ, the Calycanthus order.—Shrubs with quadrangular stems, having four woody axes surrounding the central one, opposite, entire, exstipulate leaves, and solitary lurid flowers. Calyx of numerous coloured sepals confounded with the petals, and all united below into a fleshy tube, bearing numerous stamens on its rim. Outer stamens extrorse; inner, sterile. Ovaries several, one-celled, adherent to the calcine tube; ovules one or two. Fruit, achene inclosed by the calyx. Seed exalbuminous; cotyledons convolute. The plants are found in North America and Japan. Their flowers have an aromatic fragrance, and their bark is sometimes used as a carminative. Calycanthus floridus, Carolina Allspice, furnishes a bark which is sometimes used in place of Cinnamon.

Nat. Ord. 79.—Lythraceæ, the Loosestrife order.—Herbs, rarely shrubs, often with quadrangular branches, with usually opposite, and entire exstipulate leaves. Among the allied exalbuminous perigynous orders it is distinguished by its tubular calyx inclosing a 2-6-celled ovary which is free from it, its united styles, membranous capsular fruit, and stamens inserted on the calcine tube below the petals. The plants are chiefly tropical; some are found in Europe and in North America. Astringency is met with in many plants of the order. Some of them furnish dyes. Lawsonia tinctoris is the Henna or Alkanna of Cyprus and Egypt, which is used in the East for dyeing the nails, the palms of the hand, and the soles of the feet, of an iron-rust colour.

Nat. Ord. 80.—Rhizophoraceæ, the Mangrove order.—Trees or shrubs, with simple, opposite leaves, having deciduous interpetiolar stipules. Calyx adherent, with 4-12 valvate lobes. Petals 4-12. Stamens twice or thrice as many. Ovary 2-4-celled, with 2 pendulous ovules in each cell. Fruit monospermal, indehiscent, crowned by the calyx. Seed exalbuminous; embryo germinating in the pericarp. The plants grow in the unhealthy maritime swamps of the tropics. Mangroves have usually astringent barks, employed as febrifuges and for tanning. Some are used for dyeing black. Rhizophora Mangle, the Mangrove tree (Fig. 67), has remarkable aerial roots. Its bark is used for tanning.

Nat. Ord. 81.—Vochysiaceæ, the Vochysia order.—Trees or shrubs, with their young branches often quadrangular, leaves entire, usually opposite and stipulate. Sepals 4-5, upper one spurred. Petals 1-5, unequal. Stamens 1-5. Fruit a triquetrous, 3-celled capsule, with a central placenta. Seeds exalbuminous, usually winged. Found in equinoctial America. Some of the plants are timber trees.

Nat. Ord. 82.—Combretaceæ, the Myrobolan order.—Trees or shrubs, with alternate or opposite, entire, exstipulate leaves, often petiolate. They are distinguished from the orders near them by their one-celled ovary, containing 2-4 suspended ovules, but only a single seed in the fruit, and convolute cotyledons. Natives of tropical regions. The plants of this order have astringent properties. Some species are cultivated for ornament; others yield timber. Terminalia belerica, and T. Chebula, yield the astringent fruit known by the name of Myrobolans.

Nat. Ord. 83.—Melastomaceæ, the Melastoma order.—Trees, shrubs, or herbs, with opposite, ribbed leaves, and showy flowers. The anthers are long, rostrate, and bent down parallel to the filaments in aestivation, lying in spaces between the calyx and ovary. The plants differ from Lythraceæ in the calyx-lobes not being valvate, and from Myrtaceæ in the leaves not being dotted. Memecylon has sometimes been made the type of a separate order on account of its adherent calyx, ribless leaves, and convolute cotyledons. The plants of this order are chiefly tropical. They possess Botany.

Nat. Ord. 84.—**Alangiacae**, the Alangium order.—Trees or shrubs, with branches often spiny, leaves entire, alternate, exstipulate, and without dots. Calyx adherent, 5-10-toothed. Petals 6-10, linear, reflexed. Stamens equal in number to the petals, or two or four times as many; filaments villous at the base; anthers adnate, linear. Fruit a drupe adherent to the calyx. Seed anatropal, pendulous, albuminous; cotyledons flat. Natives of India and North America. Many of the plants supply timber; others have edible fruits. Some are aromatic.

Nat. Ord. 85.—**Philadelphiaceae**, the Syringa order.—Shrubs, with opposite, deciduous, exstipulate, dotless leaves. Calyx adherent; 4-10-lobed, valvate. Petals alternate with the calycine segments. Stamens indefinite. Styles distinct or united. Fruit a half-inferior 4-10-celled capsule, with an axile placentum. Seeds albuminous. The species are scattered over Europe, North America, and India. The flowers of *Philadelphus coronarius*, common garden Syringa, have an overpowering odour, and yield an oil. It is called Mock Orange in America. The leaves of the plant taste like Cucumbers. The leaves of the species of *Deutzia*, especially *D. scabra*, are covered with beautiful star-like hairs or scales.

Nat. Ord. 86.—**Myrtaceae**, the Myrtle order (Fig. 475). Trees or shrubs, with entire, exstipulate, usually opposite and dotted leaves, often having an intramarginal vein. Calyx adherent (Fig. 476), cleft, sometimes operculate. Petals 4-5, sometimes none. Stamens usually 2 with long filaments and ovate anthers. Style simple. Fruit baccate in true Myrtaceae and capsular in Leptospermum. Seeds usually numerous, exalbuminous. Tropical and sub-tropical plants. The plants of this order are generally aromatic, and yield a pungent volatile oil. Some of them are astringent, others yield gummy and saccharine matter. The unexpanded flower-buds of *Caryophyllus aromaticus* constitute the Cloves of commerce. *Eugenia Pimenta* bears an aromatic fruit, having the flavour of Cloves, Cinnamon, and Nutmeg, and which, when dried, constitutes Allspice, Pimento, or Jamaica Pepper. The leaves of *Melaleuca minor* furnish the green pungent oil of Cajeput. Species of *Paidium* supply the fruit called the Guava. *Punica Granatum* yields the Pomegranate.

Nat. Ord. 87.—**Chamaelauciacae**, the Fringe-Myrtle order.—Small heath-like bushes, with evergreen leaves abounding in oil. Allied to Myrtaceae, but differing in their fringed or feathery calyx, sterile staminal row, and 1-celled ovary. They are fragrant New Holland plants.

Nat. Ord. 88.—**Leptidicaceae**, the Monkey-pot order.—Large trees, with stipulate leaves and showy flowers. Allied to Myrtaceae, but distinguished by their large almond-like seeds, their alternate, dotless leaves, and by their stamens being in part collected into a hooded plate. The fruit is a woody capsule, often with circumscissile dehiscence (Fig. 311). Natives of the warm regions of South America. Many of the plants yield edible seeds. Their seed-vessels are sometimes used as cups and bowls, and their wood is put to economic uses. The seeds of *Bertholletia excelsa* are the Brazil or Castanha nuts of the shops. *Lecythis ollaria* is one of the largest trees in the Brazilian forests. Its seed-vessel receives the name of Monkey-pot. The seeds are called Sapucaya nuts.

Nat. Ord. 89.—**Barringtoniacae**, the Barringtonia order.—Trees or shrubs referred by most authors to the Myrtle alliance, but distinguished by the presence of a large quantity of albumen, alternate, dotless, and often serrated leaves. The fruit is pulpy. Natives of the tropics. The bark of some of the plants is bitter and tonic.

Nat. Ord. 90.—**Onagraceae**, the Evening-Primrose order (Fig. 477).—Herbs or shrubs, with alternate or opposite, simple, exstipulate, dotless leaves, and showy tetramerous flowers. Calyx superior, tubular, limb 4-lobed, valvate. Petals usually 4, twisted in aestivation. Stamens epigynous, generally 4 or 8; pollen triangular (Fig. 269). Ovary 2-4-celled; styles united; stigma capitate or 4-lobed. Fruit capsular or baccate. Seeds exalbuminous. Chiefly natives of the temperate parts of America. The plants of this order have mucilaginous and astringent properties. Some yield edible roots and fruits. *Fuchsia* is remarkable for its coloured calyx and succulent subacid fruit. *Oenothera*, Evening Primrose, is so called, because many of the species open their flowers at night.

Nat. Ord. 91.—**Haloragaceae**, the Hippuris or Mare’s-tail order.—Herbs or undershrubs, often aquatic, with alternate, opposite, or whorled leaves, and small, frequently incomplete flowers. They may be regarded as an imperfect form of Onagraceae, from which they are distinguished by their minute calyx, and their solitary pendulous seeds. They are frequently apetalous, and the stamens are sometimes reduced to one. They are found in all quarters of the globe. Some of the plants of the order yield edible seeds; others have a fragrant odour. The Water-Chestnut furnishes edible seeds. A remarkable horned fruit like the head of a bull.

Nat. Ord. 92.—**Loasaceae**, the Loasa or Chili-Nettle order.—Herbs with rigid or stinging hairs, opposite or alternate, exstipulate leaves, and showy flowers. Calyx adherent, limb 4-5-parted. Petals 5 or 10, often cucullate. Stamens 2, distinct or united in bundles. Ovary 1-celled, with several parietal placentas; style single. Fruit capsular or succulent. Seeds albuminous. American plants, some of which receive the name of Chili-Nettles on account of the stinging property of their hairs.

Nat. Ord. 93.—**Cucurbitaceae**, the Gourd order (Figs. 478 to 480).—Succulent climbing plants, with extra-axillary tendrils (in place of stipules), alternate, palmately-veined, scabrous leaves, and unisexual flowers. Calyx adherent, limb 5-toothed or obsolete. united, reticulated. Stamens generally 5, distinct or combined; anthers long and sinuous. Ovary 1-celled, inferior, with 3 parietal placentas; stigmas thick, dilated or fringed. Fruit a pepo (Fig. 324). Seeds flat, exalbuminous; cotyledons leafy. Chiefly natives of hot countries; they abound in India and South America. The plants of the order may be said in general to possess a certain degree of acridity, which is sometimes so marked as to give rise to drastic purgative qualities. In many cases, however, as in the Melon, the Cucumber, the Vegetable Marrow, Gourd, Pumpkin, and Squash, the fruit is edible when cultivated. The seeds are usually harmless. *Bryonia alba* and *B. dioica* have large roots, which are powerful purgatives. *Citrus* (*Cucumis*), *Colocynthis*, *Coloquintida*, or Bitter Apple (Fig. 480).


**Fig. 479.**

Diagram of the female flower of the Melon, showing a similar arrangement of the floral envelopes, as in Fig. 476, an abortive circle of stamens, and the ovary, with three parietal curved placentaries sending processes towards the centre.

**Fig. 480.**

Diagram of the Cucumber plant, showing the Colocynth plant with its palmette-veined leaves, cirriose stipules on one side of the leaf, and a pulpy fruit or Pepo.

Has a round fruit, the pulp of which is the Colocynth of the shops. *Cucumis sativus* yields the common Cucumber; *C. Melo*, the Common Melon; *Cucurbita Citrullus*, the Water Melon, and *C. ovifera*, Vegetable Marrow. *Echinocactus purpureus* (*Momordica Euterium*), is called Squirting Cucumber, on account of the elastic mode in which its seeds are scattered. The feculence deposited from the juice of the fruit constitutes the hydragogue cathartic called Elaterrum.

Nat. Ord. 94.—**Papaveraceae**, the Papaw order (Fig. 481).—Trees or shrubs often having an acrid milky juice, with alternate, lobed, long-petioled leaves, and unisexual flowers. The plants are distinguished from Cucurbitaceae by not climbing, and by having a free ovary with 5 placentas and albuminous seeds. The natural order Pangiaceae may be included, which differs only in having a polypetalous corolla and scales attached to the throat of the female flower. Papayaceae are chiefly found in South America; Pangiaceae in India. Many of the Papaw-worts have an acrid milky juice, while the Pangiads are poisonous. *Carica Papaya* (Fig. 481), the Papaw-tree, has an edible fruit.

Nat. Ord. 95.—**Belvisiaceae**, the Bolvisia order.—Shrubs, with simple, alternate, leathery, extipulate leaves. Calyx, a thick coriaceous cup, with 5 segments, valvate. Corolla of 3 distinct gamopetalous rings, the first being large and conspicuous, and consisting of 5 lobes, each with 7 ribs and 7 teeth, the second being a narrow membrane cut into sharp pointed segments, the third being an inconspicuous membranous cup finely cut. Stamens 20, in an erect cup-like form, unequally united. Disk fleshy, cup-like, covering the ovary, and standing as high as the stigma.

Ovary 5-celled; ovules 2 in each cell, suspended from an axile placentas; style and stigma pentagonal. Fruit a large round berry crowned by the calyx. Seeds large and reniform. Natives of tropical Africa. The pulp of the fruit is eatable, and the rind contains so much tannin as to be used for making ink; the wood is soft, and contains numerous dotted vessels. Bentham considers the order as a section of Myrtaeae, while Lindley considers it as allied to Rhizophoraceae.

Nat. Ord. 96.—**Passifloraceae**, the Passion-flower order.—Herbs or shrubs usually climbing by tendrils, with alternate, stipulate, sometimes glandular leaves. Calyx of 5 sepals, united below, the throat bearing 5 petals and filamentous or annular processes. Stamens 5, monadelphous, surrounding the gynophore; anthers extrorse. Ovary free from the calyx, 1-celled; styles 3, club-shaped. Fruit mostly fleshy, stalked, 1-celled, with 3 parietal polyspermous placentas. Seeds albuminous, arillate. They are common in tropical America. Astringent and narcotic qualities appear to prevail in the order. Many of the species, however, produce edible fruits. *Passiflora quadrangularis* produces the granadilla, a well-known West Indian fruit.

Nat. Ord. 97.—**Homaliaceae**, the Homalium order.—Trees or shrubs with alternate leaves with or without stipules. Calyx infundibuliform, with 5-15 divisions. Petals equal in number to the segments of the calyx and alternate with them. Stamens arising from the base of the petals, either singly or in bundles of 3 or 6. Ovary adherent, 1-celled; ovules numerous, pendulous; placentas 3-5, parietal; styles 3-5. Fruit a capsule or berry. Seeds albuminous. Tropical plants of India, Africa, and America, having astringent properties.

Nat. Ord. 98.—**Tinneviaceae**, the Turnera order.—Herbs, sometimes shrubby plants, having a Cistus-like habit, with alternate, extipulate, pubescent leaves. Calyx 5-lebed, bearing 5 petals and 5 stamens. Ovary free, 1-celled, with 3 parietal placentas and 3 styles which are often forked or multilobed at the apex. Fruit a 3-valved capsule. Seeds albuminous, strophiolate at one side. The plants have astringent, tonic, and occasionally aromatic qualities, and are natives of South America and the West Indies.

Nat. Ord. 99.—**Portulacaceae**, the Purslane order.—Succulent herbs or shrubs, with alternate or opposite, entire, extipulate leaves. Calyx of 2 coherent sepals. Petals 5. Stamens variable in number, sometimes opposite the petals; anthers versatile. Ovary 1-celled, formed of 3 united carpels. Fruit capsular, usually dehiscent by valves or by a lid. Seeds numerous, albuminous, attached to a central placenta; embryo peripheral. This order has the stamens sometimes hypogynous, and it has been placed near Caryophyllaceae by some authors. The plants are found in dry places, in various parts of the world, more particularly in South America and at the Cape of Good Hope. Esculent and antiscorbutic qualities prevail in the order. Some have showy flowers which are ephemeral.

Nat. Ord. 100.—**Illecebraceae** or **Paronychiaceae**, the Knotwort order.—Herbaceous or suffruticose plants, with opposite or alternate, often clustered, sessile, entire, stipulate leaves, and minute flowers. Sepals 3-5, distinct or cohering. Petals small, sometimes 0. Stamens opposite the sepals, if equal to them in number. Ovary superior; styles 2-5. Fruit dry, 1-3-celled, indehiscent or opening by 3 valves. Seeds either numerous and attached to a free axile placenta, or solitary and pendulous from a cord attached to a basal placenta. Seeds albuminous; embryo curved. This order is by some placed near Caryophyllaceae, from which it differs in the presence of scarious stipules and in its perigynous stamens. The plants are... natives chiefly of barren places in the south of Europe and north of Africa, and their properties are astringent.

Nat. Ord. 101.—Crassulaceae, the Stonecrop order (Fig. 482 and Fig. 217).—Succulent herbs or shrubs, with exstipulate leaves and cymose, often secund flowers. Sepals 3-20, more or less combined. Petals 3-20, separate or united. Stamens equal in number to the petals, or twice as many. Carpels 1-celled, of the same number as the petals, having hypogynous scales at their base. Fruit follicular. Seeds numerous, albuminous. Natives of dry places in all parts of the world. Acidity prevails in many plants of this order. Some species are refrigerant, others astringent. Bryophyllum calycinum has a gamopetalous corolla, and produces marginal buds on its leaves (Fig. 141). Sedum Telephium has been employed in diarrhoea as an astringent. S. acre, Biting Stonecrop, possesses acidity, and has emetic and purgative properties.

Nat. Ord. 102.—Mesembryanthemaceae or Ficoides, the Fig-Marigold order.—Succulent shrubs or herbs, with opposite simple leaves and often showy flowers. Sepals 4-8, more or less united. Petals and stamens 5. Capsule usually many-celled, opening in a stellate manner; placentae central or parietal. Seeds numerous, albuminous; embryo curved or spiral. Natives of the hot sandy plains of the Cape of Good Hope; a few also are found in Europe, South America, and China. Some of the plants are esculent, others furnish alkaline matter, while a few are diuretic. Mesembryanthemum crystallinum is called the Ice-plant, on account of the watery vesicles on its surface.

Nat. Ord. 103.—Tetragoniacae, the Tetragonia order.—Succulent plants nearly allied to Fig-Marigolds, but differing in the want of petals and in having definite stamens. The fruit is either an indehiscent nut or a pyxidium. They are found in the South Sea Islands, the Mediterranean, and the Cape of Good Hope. Many of them are saline, others are esculent. Tetragonia expansa is used as Spinage in New Zealand.

Nat. Ord. 104.—Cactaceae, the Cactus order (Figs. 483 and 484).—Succulent often spiny herbs, with remarkable stems, which are angular, two-edged, or leafy, and have their woody matter often arranged in a wedge-like manner. Calyx of numerous sepals combined and epigynous. Petals indefinite. Stamens 5, with long filaments. Ovary 1-celled, with parietal placentas; style single; stigmas several. Fruit baccate. Seeds exalbuminous. Natives of America. The fruit of many of the Indian Figs is subacid and refreshing. In some instances, it is sweetish and insipid. The stems of some of the species are eaten by cattle. The plants of the Cactus tribe present remarkable stems; sometimes spherical (Fig. 142), sometimes articulated or jointed (Fig. 483), and sometimes assuming the form of a tall upright polygonal column. Cereus grandiflorus is a night-flowering plant, so is also C. nycticus and some other species. Opuntia cochinellifera, the Nopal plant, affords nourishment to the Coccus Cacti or Cochineal insect in Mexico and Peru.

Nat. Ord. 105.—Grossulariaceae, the Gooseberry order.—Shrubs which are either spiny or prickly or unarmed, with alternate palmately-lobed leaves without true stipules. Calyx-tube adherent to the ovary, limb 4-5-lobed, sometimes coloured. Petals small, 5. Stamens 5. Ovary 1-celled, with 2 parietal placentas; styles more or less united. Fruit a berry, crowned with the remains of the flower, with two parietal placentas (Fig. 323). Seeds numerous, albuminous; embryo minute. Natives of the temperate regions of Europe, Asia, and America. Whole-some plants, furnishing often edible fruits, containing malic and other organic acids. Ribes Grossularia, the Gooseberry; R. nigrum, the Black Currant; R. rubrum, the Red Currant, furnish valuable fruits.

Nat. Ord. 106.—Escalloniaceae, the Escallonia order.—Evergreen shrubs, often odoriferous, with alternate exstipulate leaves, allied to the last order, and differing from it in their capsular bicarpellary fruit, epigynous disk, axile placentas, and oily albumen. By some they are placed among Saxifragaceae, from which they differ in their simple style and oily albumen. Natives chiefly of South America. Escalloniae attain a high elevation on the mountains.

Nat. Ord. 107.—Saxifragaceae, the Saxifrage order (Fig. 485).—Herbs with alternate leaves. Calyx of 4-5 more or less coherent sepals. Petals 5 or 0. Stamens 5-10. Ovary more or less completely inferior, consisting of 2 carpels which diverge at the apex. Fruit a 1 or 2-celled capsule. Seeds numerous; embryo straight in fleshy albumen. Natives of northern alpine districts. Their properties are astringent. Heuchera americana is called alum-root on account of its astringency.

Nat. Ord. 108.—Hydrangeaceae, the Hydrangea order.—Shrubs with simple exstipulate leaves, often considered as a sub-order of Saxifragaceae, but differing in their opposite leaves, their tendency to form abortive radiant flowers, and in the carpels being often more than two. Natives of the temperate regions of Asia and America. Hydrangeas from China and Japan are commonly cultivated. Some of the species are used instead of Tea.

Nat. Ord. 109.—Cunoniaceae, the Cunonia order.—Trees or shrubs allied to Saxifragaceae, and differing in their shrubby growth, opposite leaves, and interpetiolar stipules. The latter character separates them from Hydrangeas, which are exstipulate. Natives of the Cape of Good Hope, South America, the East Indies, and Australia. Their properties are astringent.

Nat. Ord. 110.—Bruniaceae, the Brunia order.—Heath-like shrubs, with small, rigid, entire leaves. Calyx usually superior, 5-cleft. Petals and stamens 5; anthers extrorse. Ovary 1-3-celled, with 1-2 suspended ovules in each cell; style simple or bifid. Fruit either dehiscent and 2-celled, or indehiscent and 1-celled. Seeds solitary or in pairs. Botany. embryo minute, in fleshy albumen. Natives chiefly of the Cape of Good Hope.

Nat. Ord. 111.—HAMAMELIDACEAE, the Witch-Hazel order.—Trees or shrubs, with alternate, feather-veined leaves, having deciduous stipules. Calyx 4-5-divided. Petals 4, 5, or 0. Stamens 8; anthers introrse. Ovary 2-celled, inferior; ovules solitary or several; styles 2. Fruit a 2-valved loculicidal capsule. Seeds pendulous, albuminous. Natives of North America, Asia, and Africa. *Rhododendron Championi* is a showy plant, with red involucral leaves, found in China. *Hamamelis virginiana* furnishes edible oily seeds.

Nat. Ord. 112.—UMBELLIFERAE or APIACEAE, the Umbelliferous order,* (Figs. 486, 487).—Herbs with solid or hollow stems, alternate leaves generally compound and sheathing at the base, and umbellate involucrate flowers (Fig. 163). Calyx adherent to the bicarpellary ovary, limb 3-toothed or obsolete. Petals 5, inflexed at the point (Fig. 319), often unequal, the outer ones being radiant. Stamens 5, alternate with the petals, and inserted with them on the outside of an epigynous disk or stylodip (Fig. 319). Styles 2. Fruit a cremocarp (diachnum), the 2 carpels or mericarps separating when ripe by their inner faces or commissure, and being suspended by a forked carpophore (Fig. 320); the carpels marked with ribs or ridges called juga and intervening spaces called valleculae, and often containing vittae. Seed solitary, pendulous; embryo minute, in the base of horny albumen. The Sections formed from the nature of the albumen, whether flat or curved, are not now adopted, inasmuch as they are found to be unsatisfactory. In the genera, the ridges on the fruit, the presence or absence of vittae, and the form of the albumen, are taken into account. The umbels are sometimes reduced to a sort of head by the absence of peduncles. Natives of the northern parts of the northern hemisphere, and found high on the mountains of the tropics.

The properties of Umbelliferous plants are various. Some are harmless and esculent, such as the Carrot, Parsnip, Skirret and Parsley; others are acro-narcotic poisons, as Hemlock; a third set are antispasmodic, owing to the presence of a gum-resin containing a fetid sulphur oil, such as Asafoetida; while a fourth set are carminative from containing a volatile oil, as Caraway (*Carum Carvi*), and Coriander (*Coriandrum sativum*). *Conium maculatum*, Hemlock,* used medicinally as an anodyne, contains a very active volatile oleaginous alkali called Conia, which causes death by paralysing the muscles of respiration. *Dorema Ammoniacum*, or *Disermentum gummosferum*, a Persian plant, yields gum Ammoniac. *Narthex Asafoetida*, a plant found in Persia and Afghanistan, furnishes the true Asafoetida. *Opoponax Chironum*, or *Pastinaca Opoponax*, produces the gum-resin called Opoponax.

Nat. Ord. 113.—ARALIACEAE, or HEDERAceAE, the Ivy order.—Trees, shrubs, or herbs with the habit of Umbellifere, from which they differ in having the ovary composed of more than 2 carpels which do not separate in fruit, but become drupaceous or baccate, and in having fleshy in place of horny albumen. They are found in tropical and sub-tropical regions. The properties of the order are aromatic, stimulant, and tonic. *Aralia poppyfera*, Bokshung of China, found in the island of Formosa, is the plant which supplies the Chinese Rice paper. The black berries of *Hedera Helix*, common Ivy, are emetic and purgative. *Panax Schinseng* is the Asiatic Ginseng root, extravagantly prized by the Chinese as a stimulant and restorative.

Nat. Ord. 114.—CORNACEAE, the Cornel order.—Chiefly trees or shrubs, with leaves almost always opposite and stipulate; flowers in cymes or in involucrate heads. Calyx adherent, limb 4-toothed. Petals 4, valvate in aestivation. Stamens 4, alternate with the petals. Styles united into one. Ovary 2-celled; ovules solitary, pendulous. Fruit a 2-celled drupe. Embryo in fleshy albumen. Natives of the temperate regions of Europe, Asia, and America. The plants of this order have tonic and febrifugal properties. Some are astringent. The bark of various species of *Cornus*, as *C. florida*, *C. sericea*, and *C. circinata*, are used as substitutes for Cinchona in the United States.

2. Monopetalae or Gamopetalae.

Nat. Ord. 115.—LORANTHACEAE, the Mistletoe order (Fig. 488)—Parasitic shrubs with articulated branches, opposite exstipulate fleshy leaves, and hermaphrodite or unisexual flowers. Calyx tube adherent to the ovary, bracteated. Corolla of 4-8 united petals. Stamens 4-8, opposite the petals. Ovary 1-celled; ovule solitary, pendulous. Fruit inferior, succulent. Albumen fleshy. In place of one order, Miers makes two, Loranthaceae and Viscaceae. *Loranthus*, which is the type of the first, has showy dichlamydaceous hermaphrodite flowers, lengthened stamens, and an ovary containing a solitary suspended ovule; while *Viscum* (Fig. 488), the type of the second, has small, monochlamydaceous dioecious flowers, with nearly sessile stamens, and an ovary containing 3 ovules attached to a free central placenta, one of the ovules only being perfected in the baccate fruit. The order Viscaceae is placed near Santalaceae. Natives chiefly of the equinoctial regions of Asia and America; a few are European and African. Astringent properties prevail in the order. The plants are truly parasitic, and they have often a peculiar woody structure with scalariform vessels. Occasionally 2 or 3 embryos are produced in the seed.

Nat. Ord. 116.—CAPRIFOLIACEAE, the Honey-suckle order.—Shrubs or herbs, often twining, with opposite, exstipulate leaves (Fig. 137). Calyx adherent to the ovary, limb 4-5-cleft, usually bracteated. Corolla regular or irregular. Stamens 4-5, alternate with the corolline lobes. Ovary 3-5-celled; stigmas 3-5. Fruit usually a berry, one-celled, crowned by the calyx-lobes. Albumen fleshy. Natives chiefly of the northern parts of Europe, Asia, and America. Some of the plants are astringent, others have emetic and purgative properties. Many have showy and fragrant flowers. *Loniceria Periclymenum*, common Honey-suckle or Woodbine, possesses emetic and purgative qualities. The flowers of *Sambucus nigra*, common Elder, yield a volatile oil, and the berries are used in making a kind of wine.

Nat. Ord. 117.—CINCHONACEAE, the Cinchona order Botany. (Figs. 489 to 491).—Trees, shrubs, or herbs, with simple opposite leaves, interpetiolar glandular stipules and cymose inflorescence. Calyx adherent, entire, or toothed. Corolla regular. Stamens attached to the corolla. Ovary 2-celled; style 1. Fruit inferior, separating into 2 cocci, or indehiscent and dry, or succulent. Seeds definite and erect or ascending, or indefinite and attached to a central placenta; embryo small, in horny albumen. Chiefly found in tropical regions. This extensive order furnishes many important products. The plants have tonic, stimulant, febrifugal, emetic, and purgative properties. Some species are said to have intoxicating and even poisonous qualities. Many of the plants of the order have flowers remarkable for their beauty and odour. *Cephaelis Ipecacuanha* (Fig. 490) has an annulated root which is the Ipecacuan of the Pharmacopoeias. It is emetic and diaphoretic, and contains a principle called Emetine. *Cinchona* (Fig. 489), is the genus which furnishes the species of Peruvian-bark trees. They contain three important alkalies, Quinine, Quinidine, and Cinchonine, combined with Kinic acid, and a peculiar variety of tannin. *Coffee arabica* (Fig. 491), the Coffee tree, has a succulent fruit of a reddish-brown colour when ripe. The hard albumen is used to furnish the well-known beverage. It contains a bitter principle called Caffeine, which is identical with Theine. An astringent extract called Gambeer is prepared by the Malays from the leaves of *Uncaria Gambir*.

Nat. Ord. 118.—GALIACEAE or STELLATE, the Madder order (Fig. 492).—Herbs agreeing in most points with Cinchoaceae, and often included with them in a common order called Rubiaceae. The chief distinguishing marks are their square stems, verticillate and exstipulate leaves. The name Stellate is derived from the star-like arrangement of the leaves. Some look upon the verticils as made up partly of true leaves, and partly of stipules. Natives of the northern parts of the northern hemisphere and of high mountains in South America and Australia. The plants supply important dyes. Some have tonic and diuretic properties. The horny albumen of *Gaium Aperine* has been used for Coffee. *Rubia tinctorum*, Madder root, is a most important dye-stuff used in giving the colour called Turkey-red. The roots of *R. cordifolia* (*Munista*) furnish the dye called Munjet in India.

Nat. Ord. 119.—VALERIANACEAE, the Valerian order, (Figs. 493 to 495).—Herbs with opposite exstipulate leaves and cymose inflorescence. Calyx superior (Fig. 494), limb obsolete or forming a kind of pappus (Fig. 495). Corolla tubular, 3-6-lobed, sometimes gibbous, or spurred at the base (Fig. 494). Stamens 1-5, inserted on the corolla. Ovary with one cell and 2 abortive ones; ovule solitary. Fruit dry and indehiscent, with 1 fertile cell, sometimes papoose (Fig. 495). Seed suspended, exalbuminous. Natives of temperate climates in Europe, Asia, and America. Many of the plants in the order are strong-scented or aromatic, owing to the presence of a peculiar volatile oil. In medicine, they are employed as tonics and antispasmodics. The leaves of *Centranthus ruber*, Red Valerian, are used as a salad. *Nardostachys Jatamansi* appears to be the plant which supplied the ancient Spikenard. *Valeriana officinalis* furnishes the Valerian root of the druggists, which yields Valerianic acid, and is used as an antispasmodic in nervous affections.

Nat. Ord. 120.—DIPSACACEAE, the Teazel order.—Herbs or undershrubs, with opposite or whorled, exstipulate leaves, and flowers in capitula surrounded by an involucre. Calyx adherent, membranous, surrounded by an involucre. Corolla tubular, with an oblique 4-5-lobed limb. Stamens 4, anthers distinct. Ovary 1-celled; ovule pendulous. Fruit dry, indehiscent, crowned by the pappus-like calyx. Seed albuminous. Natives of the south of Europe, the Mediterranean, and the Cape of Good Hope. Some of the species are used in dressing cloth. Astringent qualities reside in some of the plants. The dried heads of *Dipsacus Fullonum*, Fuller's Teazel, with their uncinate spiny bracts, are used by fullers.

Nat. Ord. 121.—CALYCERACEAE, the Calycera order.—A small order of herbs with alternate exstipulate leaves, and capitate flowers, intermediate between Dipsacaceae and Composite, differing from the former in their united filaments and partially united anthers, and from the latter in their pendulous ovule, albuminous seed, and in their anthers. They inhabit the cooler parts of South America.

Nat. Ord. 122.—COMPOSITE or ASTERACEAE, the Composite order (Figs. 496 to 499).—Herbs or shrubs with alternate or opposite, exstipulate leaves, and hermaphrodite or unisexual flowers (called florets) collected into dense capitula on a common receptacle (Figs. 496 and 174), and surrounded by a set of bracts (called phyllaries), forming an involucre (Fig. 161), the separate florets being often furnished with bractelets in the form of chaff (called squama or palea). Calyx adherent, limb entire or toothed, or mostly Botany, expanded into a pappus (Fig. 228). Corolla regular or irregular (Figs. 497 and 498). Stamens 5; anthers syn-

genious (Fig. 252). Ovary single; style 1, bifid at the apex when fertile (Fig. 498); stigmas on the inner surface of each branch of the style (Fig. 499). Fruit an achene,

crowned with the limb of the calyx (Fig. 155). Seed solitary, erect, exalbunous; embryo straight. The plants are found in all parts of the world. In warm countries they sometimes assume arborecent forms. There are between 9000 and 10,000 known species.

The plants of this very extensive order have been variously divided by authors. They were included by Linnaeus in his class Syngenesia, the divisions of which have been already given. By Jussieu the following divisions have been established:—1. Cichoraceae, the florets all ligulate and perfect. Ex. Cichorium. 2. Cynarocephale, the florets all tubular, homogamous, or those of the ray neuter; style swollen below its branches. Ex. Carduus. 3. Corymbiferac, florets of the same head all homogamous (usually tubular); or those of the circumference filiform or tubular and pistilliferous, or ligulate; style of the perfect florets not swollen below its branches. Ex. Anthemis. De Candolle gives the following primary divisions:—1. Tubuliflorae (embracing Cynarocephale and Corymbiferac of Jussieu), hermaphrodite flowers, tubular, with 5, rarely 4, equal teeth. 2. Labiatiflorae, hermaphrodite flowers, or at least the unisexual ones, two-lipped. This includes chiefly some peculiar American genera. 3. Liguliflorae (Cichoraceae of Jussieu), all the florets hermaphrodite and ligulate. Under these sub-orders De Candolle formed tribes from the form and nature of the style and stigma, attention being paid to the mode in which the branches of the style separate, the nature and extent of the papilla, and the hairs on the stigmatic surface and on the style, &c.

The properties of Composite plants are various. Bitterness seems to prevail in the order to a greater or less degree. This is accompanied with tonic, stimulant, aromatic, or even narcotic qualities. Cichorium Intybus Chicory, or Wild Succory (Fig. 375), is much cultivated, especially in France and Germany. Its roots are used as a substitute for Coffee, or as an addition to it. C. Endivia is the Endive or garden Succory, the leaves of which are used as a salad when etiolated. Lactuca virosa, Wild Lettuce, gives out abundantly a white juice which, when inspissated, constitutes the analgetic narcotic called Lactucarium, or Lettuce-opium. L. sativa, common Lettuce, also yields a similar juice. Leontodon Taraxacum, common Dandelion, has a milky juice which, when concrete, has been used medicinally as a diuretic, and economically as Coffee. The dried flowers of Carthamus tinctorius, Safflower, yield a pink dye. Cynara Scolymus, or the common Artichoke, has a succulent receptacle, which is used for food. Anacyclus Pyrethrum, Pellitory of Spain, is used medicinally to promote the flow of saliva. The flowers of Anthemis nobilis, Chamomile, act as an emetic and diaphoretic; the extract is bitter tonic. Arnica montana, Leopard's-bane, or Mountain Tobacco, has been given in nervous diseases as an acid stimulant. Artemisia Absinthium, and other species of Wormwood, are bitter stomachic, and anthelmintic.

Nat. Ord. 123.—Brunoniaceae, the Brunonia order.—Herbs with radical exstipulate leaves, and capitulate, involucrate flowers supported on scapes. Calyx free, in 5 divisions. Corolla 5-parted, inserted at the base of the calyx. Stamens inserted with the corolla. Ovary 1-celled; ovule solitary; stigma inclosed in a 2-valved cup. Fruit a utricle, inclosed in the hardened calycine tube. Seed erect, exalbunous. Australian plants.

Nat. Ord. 124.—Goodeniaceae, the Goodenia order.—Herbs, rarely shrubs, not lactescent, with scattered exstipulate leaves, and distinct, not capitate flowers. Calyx usually superior, 3-5-divided. Corolla more or less superior, usually irregular, with a split tube and a 5-parted lipped limb; aestivation duplicandate. Stamens 5, separate. Ovary 1-2-celled; placentas free, central; stigma surrounded by an indusium. Fruit capsular or drupaceous. Seeds albuminous. Natives chiefly of Australia, and the islands of the southern ocean. Some of the plants are used as esculent vegetables, and their pith is employed for economical purposes. Scorola Tacea furnishes Rice-paper in the Malay Archipelago.

Nat. Ord. 125.—Stylidiaceae, the Stylewort order (Fig. 380).—Herbs or undershrubs, with scattered or whorled exstipulate leaves. Calyx adherent, with 2-6 divisions. Corolla usually irregular, 5-6-divided; aestivation imbricate. Stamens 2; filaments united with the style into a column; anther-lobes on the top of the column lying over the stigma. Ovary usually 2-celled, often with 1 or 2 epigynous glands in front. Fruit usually a 2-celled and 2-valved capsule. Seeds albuminous. Peculiar plants, remarkable for their gynandrous structure and for their irritable column. Natives chiefly of the swamps of Australia.

Nat. Ord. 126.—Campanulaceae, the Hare-bell order with alternate exstipulate leaves, and usually showy blue or white flowers. Calyx superior, limb commonly 5-lobed, persistent (Fig. 501). Corolla regular, campanulate, usually 5-lobed, marcescent (Fig. 501 and Fig. 219). Stamens 5, distinct. Style with collecting hairs (Fig. 384). Fruit a 2 or many-celled capsule, loculicidal, dehiscing by openings at the sides or by valves at the apex. Seeds numerous, albuminous, attached to a central placenta. Chiefly natives of the northern parts of Europe, Asia, and North America. Those with capsules opening by lateral pores appear to be natives of the northern hemisphere; those with apical valves, of the southern. The Belloworts have an acid milky juice, but occasionally the young shoots and roots are cultivated as articles of food. *Campanula Rapunculus*, Rampion, is used as an esculent vegetable.

Nat. Ord. 127.—*Lobeliaceae*, the Lobelia order.—Lac-tescent herbs or shrubs, with alternate, exstipulate leaves. Calyx superior, limb often 5-lobed. Corolla irregularly 5-lobed, often deeply cleft. Stamens 5, epigynous, synantherous. Stigma fringed. Fruit capsular, 1 or more celled, dehiscing at the apex. Seeds numerous, albuminous. Natives chiefly of tropical or sub-tropical climates. The Lobelias have usually an acro-narcotic milky juice, and hence the species are often poisonous. The milky juice is sometimes used for caoutchouc. *Lobelia inflata*, a North American species, is used medicinally under the name of Indian Tobacco, as an antispasmodic and sedative, as well as an emetic.

Nat. Ord. 128.—*Styracaceae* or *Symplocaceae*, the Storax order.—Trees or shrubs, with alternate, exstipulate leaves, usually with stellate tomentum. Calyx free, persistent, with 5 or 4 lobes, or entire. Corolla 5 or 10-divided. Stamens definite or indefinite, arising from the corolla, more or less cohering. Ovary 3-5-celled. Ovules partly erect and partly pendulous. Fruit succulent, inclosed by the calyx, often unicellular by abortion. Seeds albuminous. Miers divides this into two orders, Styracaceae and Symplocaceae, the former distinguished by their uniserial stamens, linear anthers, superior ovary, free central placenta, one-seeded drupe, and stellate hairs. Sparingly distributed, chiefly in tropical and subtropical regions. Some of the plants are bitter and aromatic, others yield a fragrant stimulant resin. *Styrax Benzoin*, a tree of the Malay Archipelago, produces the concrete balsamic exudation Benzoin, which is employed medicinally as an expectorant, and is also used for incense. *S. officinale*, a native of Syria, produces the resin called Storax, which is prescribed as a pectoral remedy.

Nat. Ord. 129.—*Columelliaceae*, the Columellia order.—Evergreen shrubs or trees, with opposite exstipulate leaves and yellow flowers. Calyx adherent, 5-parted. Corolla rotate, 5-8-parted. Stamens 2, on the corolla. Anthers sinuous. Disk epigynous. Fruit a 2-celled polyspermal capsule. Seeds albuminous. A small and doubtful order, placed by Lindley in his Cinchonal Alliance. Natives of Mexico and Peru.

Nat. Ord. 130.—*Vacciniaceae*, the Cranberry order.—Shrubs with alternate exstipulate leaves. Calyx superior. Corolla 4-6-lobed. Anthers biporous, with appendages. Fruit succulent, 4-10-celled. Seeds albuminous. The order differs from Ericaceae chiefly in its epigynous calyx. Natives of temperate regions, and found often in sub-alpine swamps. Astringent properties prevail in the order. The berried fruit is subacid and eatable. *Oxycoccus palustris* (*Vaccinium Oxycoccus*), a marsh plant, produces the Cranberry in Britain. *O. macrocarpa* is the American Cranberry. *Vaccinium Myrtillus* is the Bilberry or Blueberry.

Note.—In some Calycifloral Exogens the insertion of the stamens is so near the base of the calyx, that it is difficult to separate them from Thalamifloral Exogens. This may be seen in Leguminosae and Portulacaceae. Occasionally the petals are abor-

SUB-CLASS III.—COROLLIFLORAE.

1. Hypostaminaceae.

Nat. Ord. 131.—*Ericaceae*, the Heath order* (Figs. 502, *Plate 503).—Shrubs or undershrubs with evergreen, rigid, entire, CXVIII, whorled or opposite, exstipulate leaves (Fig. 503). Calyx figs. 6-11, inferior, 4-5-cleft, persistent. Corolla 4-5-cleft. Stamens 8-10 or twice these numbers, hypogynous. Anthers 2-celled, biporous, with appendages. Ovary surrounded by a disk or scales. Fruit capsular, rarely baccate. Seeds numerous, with an adherent testa, and cylindrical embryo in the axis of fleshy albumen. They abound at the Cape of Good Hope, and occur also in Europe, America, and Asia. Some of the Heathworts are astringent, others have edible fruit, and others, such as species of *Rhododendron*, *Kalmia*, and *Ledum*, are poisonous. The species of *Erica* have no active properties. *Arbutus Unedo* bears a fleshy fruit like a Strawberry, and hence it is called the Strawberry tree. *Arctostaphylos Uva-Ursi*, Bearberry, is an astringent. An infusion of its leaves is prescribed in discharges from the mucous membrane of the bladder.

Nat. Ord. 132.—*Pyrolaceae*, the Pyrola, or Winter-green order.—Herbs, with simple leaves, generally included as a sub-order of Ericaceae, but distinguished by their habit, their more or less declinate styles, loose testa, and minute embryo at the base of fleshy albumen. Natives of northern countries. *Chimaphila umbellata* is tonic and diuretic.

Nat. Ord. 133.—*Monotropaceae*, the Monotropa, or Fir-Rape order.—Parasitic plants of a brown colour, allied to Pyrolaceae, but differing in their scaly stems, in the longitudinal dehiscence of their anthers, and in their minute embryo being at the apex of the albumen. They are also considered by many as a sub-order of Ericaceae, from which their habit, their antherine dehiscence, loose testa, and minute embryo, separate them. Chiefly found parasitic on Firs in Europe, Asia, and North America.

Nat. Ord. 134.—*Epacridaceae*, the Epacris order.—Shrubby plants, with usually alternate, simple, and parallel-veined leaves, having overlapping bases; flowers commonly pentamerous. They represent the Heaths in Australia, and differ from Ericaceae principally in having one-celled anthers without appendages. Natives of the Indian Archipelago and Australia.

2. Epicorollae or Epipetala.

Nat. Ord. 135.—*Ebenaceae*, the Ebony order.—Trees. Botany.

or shrubs not lactescent, with alternate, exstipulate, coriaceous, entire leaves, and polygamous flowers. Calyx 3-7-cleft, persistent. Corolla 3-7-cleft, often pubescent. Stamens usually twice or quadruple the number of the corolline segments; anthers with longitudinal dehiscence. Ovary 3 or several-celled; style with as many divisions; ovules 1 or 2 in each cell, pendulous. Fruit a round or oval berry; seeds large and bony, albuminous. Chiefly tropical plants. Many are found in India, a few in colder climates. The trees of this order are remarkable for their hard and valuable timber. The bark of some of the species is astringent, while the fruit is in many cases eatable. The heartwood of several species of *Diospyros* constitutes different kinds of Ebony.

Nat. Ord. 136.—Aquifoliaceae or Ilicaceae, the Holly order.—Evergreen trees or shrubs, with coriaceous, exstipulate leaves, and small axillary flowers. Calyx of 4-6 sepals. Corolla 4-6-parted. Stamens 4-6, alternate with the corolline segments; anthers dehiscing longitudinally. Ovary 2-6-celled; a single pendulous ovule in each cell. Fruit fleshy, containing from 2 to 6 macules. Embryo minute in fleshy albumen. Natives of various parts of the world, but sparingly distributed. Bitter, tonic, astringent, and emetic properties exist in the order. Some are used as tea. *Ilex Aquifolium*, the common Holly, has a tonic bark, which has been used in intermittents. *I. paraguayensis* is called Maté in South America, where its leaves are used for tea; they contain Theine.

Nat. Ord. 137.—Sapotaceae, the Sapodilla order.—Trees or shrubs, often with milky juice, alternate, coriaceous, entire, exstipulate leaves, and hermaphrodite flowers. Calyx 4-8-parted. Corolla 4-8-cleft, sometimes with numerous segments. Stamens definite, half of them petaloid and sterile; anthers extrorse. Ovary 4-12-celled, with a single pendulous ovule in each cell; style 1. Fruit baccate. Seeds with a horny testa, usually albuminous. Natives of the tropics chiefly. The fruit of many of the plants of this order is edible. The bark is bitter and febrifugal. Some furnish caoutchouc, and others fatty matter. *Achras Sapota* produces the edible Sapodilla Plum. *Bassia butyracea* has an oily fruit which furnishes a kind of butter used in Nepal. The Shea, or Galam butter of Mungo Park, is the product of another species. *Isanandra Gutta* is the Tahne-tree, which furnishes Gutta Percha.

Nat. Ord. 138.—Myrsinaceae, the Myrsine order.—Trees or shrubs, with coriaceous, exstipulate, smooth leaves, and flowers often marked with glandular dots or lines. Calyx and corolla 4-5-cleft. Stamens 4-5, opposite the corolline segments, occasionally 5 alternate sterile ones. Ovary unicellular, with a free central placenta in which the ovules are imbedded. Fruit fleshy. Seeds 1 or more, with horny albumen. The plants are said to resemble Primulaceae in everything except their arborescent habit, fleshy fruit, and pitted placenta. They are limited in their geographical range, and abound in islands with an equable temperature, as the islands of the Indian Ocean, Mauritius, Bourbon, and Madagascar. Many of them are handsome evergreen shrubs. The seeds of *Theophrasta Jussiei* supply flour for bread in St Domingo, and the fruit of *Myrsine africana* is mixed with barley for the food of asses in Abyssinia.

Nat. Ord. 139.—Jasminaceae, the Jasmine order.—Shrubs, often twining, with opposite or alternate, usually compound leaves. Calyx and corolla regular, with 5-8 divisions. Stamens 2, included within the hypercoriferous corolla. Ovary 2-celled. Fruit a double berry or capsule. Seeds with little or no albumen and a straight embryo. Natives principally of tropical India. They are remarkable for their fragrance. The oil of Jasmine is obtained from *Jasminum officinale* and *J. grandiflorum*.

Nat. Ord. 140.—Oleaceae, the Olive order (Fig. 504).—Trees or shrubs with opposite, simple, or pinnate leaves. Calyx persistent, sometimes 0. Corolla 4-cleft, sometimes of 4 petals connected in pairs, sometimes 0. Stamens usually 2. Ovary 2-celled; ovules 2, pendulous in each cell. Fruit fleshy or dry, often 1-seeded by abortion. Seeds albuminous; embryo straight. Natives of temperate climates. Some of the plants of the order have emollient and laxative properties; others are bitter, tonic, and febrifugal. Some supply oil, others manna.

*Fraxinus excelsior*, the Ash, is distinguished by its samaroid fruit. *Olea europea* (Fig. 504), the Olive, has a drupaceous fruit which yields, on expression, Olive Oil.

Nat. Ord. 141.—Salvadoraceae, the Salvadora order.—Small trees or shrubs, with opposite leaves and minute panicle flowers. Calyx of 4 minute sepals. Corolla 4-partite. Stamens 4. Ovary superior. Fruit baccate, 1-celled. Seed solitary, exalbuminous. The order is considered by Planchon as allied to Oleaceae. Natives of Syria and India. The plants are acid and stimulant, and some of them have properties like Mustard. *Saladora persica* appears to be the Mustard-plant of Scripture. It has a small seed which grows into a tree.

Nat. Ord. 142.—Asclepiadaceae, the Milkweed order.—Lactescent, often twining shrubs or herbs, having entire, usually opposite leaves, with interpetiolar stipulary cilia. Calyx 5-divided. Corolla 5-lobed, actinomorph imbricate, rarely valvate. Stamens 5; filaments usually connate; pollen in wax-like masses (Fig. 382), cohering in pairs and attached to glands at the five angles of the stigma, which is common to the two styles. Fruit consisting of two follicles, containing numerous comose seeds (Fig. 329), with thin albumen. Chiefly tropical plants, found in Africa, India, and America. The Asclepiads have acid, stimulating, purgative, diaphoretic, and emetic properties. Most of the species have milky juice containing caoutchouc. *Asclepias tuberosa*, the Butterfly-weed or Pleurisy-root, is employed medicinally in North America as a laxative and diaphoretic. *Calotropis gigantea* is the Mudar plant of Bengal. The bark is employed medicinally as an emetic and diaphoretic. *Cynanchum monspeliacum* has a purgative juice which is used at Montpellier to adulterate Scammony. *Hemidesmus indicus* is called Indian Sarsaparilla, because its roots are used in India as a substitute for that drug.

Nat. Ord. 143.—Apocynaceae, the Dogbane order (Fig. 505).—Trees or shrubs, usually milky, allied to the Asclepiadaceae, and differing from them in the contorted restoration of the corolla, distinct filaments, granular pollen, and a peculiar hourglass-like stigma (Fig. 506). Natives of the tropics of Asia, America, and Africa. Many of the plants are poisonous, some are drastic purgatives. The bark is sometimes tonic and febrifugal. The milky juice of several species supplies caoutchouc. *Vinca*, the Periwinkle, is the only British genus in the order. *Apocynum cannabinum* has emetic roots. *Aspidosperma excelsum* supplies the fluted Yaroura-wood used for paddles. *Rouellia grata* produces what is called Cream-fruit in Sierra Leone. *Tabernanemontana utilis* is the Cow-tree of Demerara. *Tanganitica venenata* yields the famous ordeal poison of Madagascar, called Tanghin.

Nat. Ord. 144.—Loganiaceae or Spigeliaceae, the Strychnia order.—Shrubs, herbs, or trees, with opposite, entire, stipulate leaves. Calyx inferior, 4-5-parted. Corolla 4, 5 or 10-cleft; aestivation convolute or valvate. Stamens varying in number, not always isomerous with the corolla. Fruit a 2-celled capsule, with loose placentas, or a berry, or succulent, with 1 or 2 nucules. Seeds usually peltate, albuminous. Chiefly tropical. The plants of this order are highly poisonous. They produce tetanic convulsions and narcotism. Some of them are used medicinally as active remedies in certain kinds of palsy. Intense bitterness is met with in some of the species, and in very moderate doses they act as tonics. *Ignatia amara*, St Ignatius's Bean, produces convulsions and death. The peltate seeds of *Strychnos Nut-Vomica* (Fig. 507), produce powerful effects on the spinal marrow, and cause death by tetanus. They contain the alkaloid called Strychnia. The bark constitutes false Aegustura.

Nat. Ord. 145.—GENTIANACEAE, the Gentian order (Fig. 508, and Fig. 159).—Herbs, rarely shrubs, with opposite, entire, exstipulate, usually ribbed leaves, and showy variously-coloured flowers. Calyx divided, persistent. Corolla persistent, imbricate, induplicate, often twisted in aestivation, sometimes with a fringed limb. Stamens alternate with the corolline segments. Ovary of 2 carpels, placed to the right and left of the axis, oncecelled, with 2 parietal, often introflexed, placentas; style 1; stigmas 2. Fruit a capsule or berry. Seeds numerous, with fleshy albumen and a minute embryo. Natives of almost all parts of the world. Some are found at an elevation of 16,000 feet, others in hot tropical plains. Bitterness is the property which prevails generally in this order. Occasionally the species have emetic and narcotic qualities. *Gentiana lutea*, the yellow Gentian of the Alps, is a medicinal plant. Its root is used as a bitter tonic.

Nat. Ord. 146.—BIGNONACEAE, the Trumpet-flower order.—Trees or twining or climbing shrubby plants, with exstipulate usually opposite and compound leaves, and showy, often trumpet-shaped flowers. Their woody stem is sometimes divided in a cruciform manner. Calyx entire or divided, often spathaceous. Corolla with a swollen throat, and a more or less irregular 4-5-lobed limb. Stamens 5, unequal, one generally abortive; sometimes didynamous. Ovary surrounded by a disk, 2-celled; carpels anterior and posterior; placentas in the axis. Fruit a 2-valved, often pod-like capsule, divided by a spurious placental dissepiment. Seeds winged, exalbuminous; embryo with broad lealy cotyledons. Natives of America. The bark of *Jacaranda bahamensis*, Palo de Buba, is used in the isthmus of Panama as an anthelmintic. *Bignonia Chica* supplies a red dye.

Nat. Ord. 147.—GESNERACEAE, the Gesnera orders (including Cyrtandraceae).—Herbs or shrubs, often growing from scaly tubers, with rugose, usually opposite and whorled exstipulate leaves, and showy flowers. Calyx half-adherent, 5-parted. Corolla more or less irregular, 5-lobed. Stamens 2, or 4, didynamous, with the rudiment of a fifth; anthers often combined. Ovary 1-celled, surrounded by a disk in the form of glands or a ring. Fruit capsular or succulent, 1-celled, with 2 lobed parietal placentas to the right and left of the axis. Seeds numerous, albuminous. They are natives of various parts of the world, chiefly the warmer regions of America. The succulent fruits are occasionally eatable, and some of the species yield a dye.

Nat. Ord. 148.—CRESCENTIACEAE, the Calabash-tree order.—Small trees, with exstipulate leaves, and flowers growing out of the old stems and branches. The plants are allied to Bignoniacae, from which they differ in their parietal placentas, their wingless seeds, fleshy cotyledons, and in the palpy contents of their woody indehiscent fruit. Natives of tropical regions. *Crescentia Cujete*, the Calabash-tree, has a gourd-like fruit with a hard shell which is used for bottles.

Nat. Ord. 149.—PEDALIACEAE, the Pedalium order.—Glandular herbs, with exstipulate leaves and large bracteated flowers. They are allied also to Bignoniacae, from which they differ in their parietal placentation, their wingless seeds with a papery episperm. From Crescentiaceae they are distinguished by the want of pulp in the fruit. The ovary, at first 1-celled, sometimes becomes divided by placental septa into 4 or 6 cells. Natives of tropical countries, especially Africa. The plants of the order have generally a heavy odour. Their seeds yield oil as well as starchy matter.

Nat. Ord. 150.—POLEMONIACEAE, the Phlox order (Fig. 509).—Herbs, with opposite or alternate leaves. Calyx 5-cleft. Corolla regular, 5-lobed, convolute. Stamens 5, alternate with the corolline lobes; pollen blue. Ovary superior, 3-celled; style 1; stigma trifid. Capsule 3-celled, 3-valved, valves separating from the axis. Seeds albuminous, often with a mucous covering containing spiral threads, which spread out in coils when water is applied. Natives chiefly of the temperate parts of America. *Polemonium caeruleum* is commonly cultivated under the name of Greek Valerian.

Nat. Ord. 151.—HYDROPHYLLACEAE, the Hydrophylum order.—Herbs or small trees, usually with alternate and lobed hispid leaves. Calyx 5-cleft, often with appendages, persistent. Corolla regular, somewhat bell-shaped. Stamens 5, alternating with the corolline lobes. Ovary superior, with 2 parietal placentas, which often line the ovary; styles 2. Fruit a 2-valved, 1-celled, or spuriously 2-celled capsule, filled with a large placenta. Seeds reticulated; embryo small in hard albumen. Natives chiefly of the temperate parts of America. Some species are tropical.

Nat. Ord. 152.—DIAPENSIAEAE, the Diapensia order.—Prostrate shrubby plants, with crowded heath-like exstipu- late leaves and solitary terminal flowers. They are in many respects allied to Polemoniaceae, from which they differ chiefly in their imbricated bracts, transversely 2-celled anthers, and peltate seeds. These characters with the 3-celled ovary also separate them from Hydrophyllaceae. Natives of northern Europe and North America.

Nat. Ord. 153.—Convolvulaceae, the Convolvulus order (Figs. 510 to 512).—Herbs or shrubs, usually twining plants yield a dye, others are used as pot-herbs. Anchusa tia.

Fig. 510. Diagram of the flower of Calystegia (Convolvulus) sepium, Great Bindweed, showing two bracts, five divisions of the calyx, five lobes of the plaited campanulate corolla, five stamens, and a two-celled ovary.

Fig. 511. Convolvulus Scammonia, the Scammony plant, found in Greece and the Levant. The concrete milky juice of the large root constitutes scammony, which is imported from Smyrna.

(Fig. 511), and lactescence, with alternate, exstipulate leaves and regular flowers, having a unifloral or multifloral cymose inflorescence. Calyx 5-divided, imbricated, persistent. Corolla plaited. Stamens 5, alternate with the corolline lobes. Ovary free, 2-4-celled; ovules 1-2 in each cell, erect; styles united, often divided at the apex. Capsule 2-4-celled, sometimes by absorption 1-celled, septifragal. Seeds large, with mucilaginous albumen; embryo curved (Fig. 512), with crumpled cotyledons. Chiefly natives of the tropics. The order is characterized by purgative properties, and it contains some important medicinal plants. Convolvulus Scammonia (Fig. 511), is the source of the purgative gum-resin, Scammony. Exogonium (Ipomea) Parga is the plant which yields Jalap.

Nat. Ord. 154.—Cucurbitaceae, the Dodder order* (Fig. 426).—Leafless parasitic twining herbs, generally reckoned a sub-order of Convolvulaceae. They are marked by scales alternating with the corolline lobes, and a filiform spiral acotyledonous embryo. The seeds germinate in the usual way, and afterwards the plants become true parasites. Some of them destroy Flax, Clover, and other crops. Natives of temperate regions.

Nat. Ord. 155.—Cordiaceae, the Sebsten order.—Trees with alternate, exstipulate, rough leaves. Calyx 4-5-toothed. Corolla 4-5-cleft, regular. Stamens alternate with the corolline segments; anthers versatile. Ovary superior, 4-8-celled; stigma 4-8-cleft. Fruit drupaceous, 4-8-celled, with a single exalbuminous seed in each cell, pendulous by a long cord. Embryo with plaited cotyledons. The plants of this order are natives of the tropics. The drupes of Cordia Myxa and C. latifolia are called Sebsten plums, and are used as food. The bark is tonic.

Nat. Ord. 156.—Boraginaceae, the Borage order (Figs. 513 and 514).—Herbs or shrubs with round stems, alternate, rough leaves, and flowers in scorpioid cymes (Fig. 170). Calyx 4-5-divided, persistent. Corolla usually regular and 5-cleft (Fig. 513 and 225), imbricate, often with fascial scales (Fig. 236). Stamens alternate with the corolline segments. Ovary 4-lobed; style basilar (Fig. 514). Fruit 2 or 4 distinct achenes. Seed exalbuminous. The plants were called Asperifolium from their rough leaves. Natives of the northern temperate regions principally. Demulcent mucilaginous qualities pervade the order. Some of the

Botany. sometimes 1, very rarely 3, are sterile; anthers dehisce longitudinally. The geographical distribution is similar to that of Solanaceae. The plants of this order are in general narcotic poisons. Their juice has the property of causing dilatation of the pupil. *Atropa Belladonna*, Deadly Nightshade,* has shining brownish-black berries. It contains an alkaloid, Atropia, to which its narcotic properties are due.

*Datura Stramonium*, Thorn-apple, is so called from its spiny capsule, which is spuriously four-celled. The leaves and seeds contain a narcotic alkaloid Daturia.

*Hyoscyamus niger*, Henbane,* is a narcotic plant, the juice of which dilates the pupil. Its seed-vessel is a pyxidium. *Mandragora officinalis*, the Mandrake, stimulates the nervous system. *Nicotiana Tabacum* (Fig. 224) supplies American Tobacco.

Nat. Ord. 161.—**Orobanchacea**, the Broom-rape order.—Leafless, scaly herbs, parasitic on the roots of other plants. Calyx 4-5-toothed, persistent. Corolla with an irregular or bilabiate limb, imbricate. Stamens 4, didynamous. Ovary 1-celled, with 2 or more parietal placentas; the 2 carpels forming the ovary placed to the right and left of the axis. Fruit a capsule, covered by the withered corolla, 1-celled, 2-valved. Seeds albuminous, minute. Natives of Europe, middle and northern Asia, North America, and the Cape of Good Hope. The properties of the order are bitter, astringent, and escharotic.

Nat. Ord. 162.—**Scrophulariacea**, the Figwort order (Figs. 517 to 519).—Herbs or undershrubs, with opposite, whorled, or alternate leaves, and anisomerous flowers. Calyx of 5 or 4 parts. Corolla irregular (Figs. 227, 229, and 230), lobes unequal, imbricate in aestivation. Stamens 2 (Fig. 230) or 4, didynamous, rarely 5, or with a rudimentary fifth (Fig. 519). Ovary bilocular, carpels anterior and posterior. Fruit capsular, rarely haccate, usually 2-celled. Seeds albuminous, with a straight or slightly curved embryo. Natives of all parts of the world, cold as well as hot. Some are root-parasites, as Eyebright, Cow-wheat, and Yellow-rattle. The Figworts are more or less suspicious in their properties. Some are acid, others sedative. There are many showy garden plants in this order. *Digitalis purpurea*, Foxglove,* is used medicinally as a diuretic and sedative of the heart's action.

Nat. Ord. 163.—**Labiacea** or **Lamiacea**, the Labiate or Dead-nettle order (Figs. 520 to 522).—Herbs or undershrubs, with tetragonal stems, opposite, exstipulate, often aromatic leaves, and flowers in verticillasters (Fig. 173). Calyx tubular, persistent, 5 or 10-toothed (Fig. 204), or bilabiate. Corolla bilabiate (Fig. 521). Stamens 4, didynamous (Fig. 253), or by abortion 2; anthers 2-celled, or 1-celled by abortion (Fig. 245). Ovary deeply 4-lobed, on a disk, style basilar (Fig. 522); stigma bifid. Fruit 1-4 achenes, inclosed by the calyx. Seeds erect, with little or no albumen. Natives of temperate climates. Labiate plants have no deleterious qualities. They are generally aromatic and fragrant. Some are tonics. Many of them, such as Lavender, Mint, Thyme, Sage, Rosemary, Marjoram, Basil, Savoury, and Hyssop, are used as carminatives and antispasmodics, and are cultivated in gardens for culinary purposes. Many contain a kind of stearpotine like camphor. Oils are procured from the leaves of most of the species, and to these their fragrance is due.

Nat. Ord. 164.—**Verbenacea**, the Vervain order (Fig. 523).—Herbs, shrubs, or trees, with exstipulate, usually opposite leaves, resembling much the Labiatae in their characters, and differing in their achenes being concrete, their style terminal, and their leaves usually not containing receptacles of oil. Corolla generally irregular. Stamens 4, didynamous, or 2; anthers 2-celled. Seeds erect or ascending; radicle inferior. Natives both of tropical and of temperate regions. In the order are included the Myoporaceae, which differ only in their seeds being pendulous and in the radicle of the embryo being superior. Bitter, tonic, as well as aromatic properties are found in the Vervains. *Verbena* was supposed to have many valuable qualities, and was an object of superstitious regard among the Druids. *Aloysia (Lippia) citriodora*, is commonly cultivated under the name of Sweet Verbena. *Tectona grandis* is the Teak-tree of India.

Nat. Ord. 165.—**Selaginacea** or **Globulariacea**, the Globularia order.—A small group of herbaceous or shrubby plants, with alternate exstipulate leaves and bracteated flowers resembling Verbenaceae, from which they differ in their 1-celled anthers, pendulous ovules, and superior radicle. *Globularia* has a solitary carpel. Allied to this order and Vervains is a small group, *Stellaceae*, of which the Cape genus *Stillea* is the type; they have slightly irregular flowers, with 4 or 5 stamens, one often abortive, anthers 2-celled, ovary 2-celled, style terminal, fruit 1-seeded, seed erect, embryo inferior. Some of the species of Selaginaceae are fragrant. They are natives of the Cape of Good Hope chiefly; some are European.

Nat. Ord. 166.—**Acanthacea**, the Acanthus order.—Herbs or shrubs, with simple, opposite, exstipulate leaves and bracteated showy flowers. Calyx of 5 sepals, distinct or combined, persistent. Corolla usually irregular, lipped. Stamens 4, didynamous, often 2 by abortion. Ovary of 2 carpels, placed anterior and posterior; placentas parietal, but extending to the axis; style 1. Fruit a 2-celled capsule, opening by elastic valves. Seeds 1, 2, or many in each cell, attached to hooked placental processes, exalbuni- Botany. Chiefly tropical plants, some of them, as *Justicia*, *Ruellia*, *Apheleandra*, and *Hexacentris*, remarkable for the beauty of their flowers. The lobed and sinuated leaves of *Acanthus* furnished the ornaments of the Corinthian capital.

Nat. Ord. 167.—**Lentibulariaceae**, the Bladderwort order.—Herbs growing in water or in wet places, with radical leaves which are either undivided or cut into filiform root-like segments bearing little bladders, and irregular showy flowers. Calyx divided, persistent. Corolla bilat- erate, irregular. Stamens 2, included; anthers 1-celled. Ovary superior, 1-celled; placentae free, central; ovules numerous. Fruit a 1-celled capsule. Seeds exalbuminous. Found in various parts of the world, most abundant in the tropics. The name Butterwort, applied to *Pinguicula*, is said to in- dicate its property of giving consistence to milk.

Nat. Ord. 168.—**Primulaceae**, the Primrose order (Figs. 524 and 525).—Herbs with opposite, or alternate, or whorled, exstipulate leaves, and flowers often on scapes. Calyx 5-cleft, rarely 4-cleft, regular, persistent. Corolla regular, 5 or 4-cleft, very rarely 0 (as in *Glaux*). Stamens opposite the corolline segments (Fig. 525). Ovary super- ior, 1-celled, with a free central placentae; style 1; stigma capitate (Fig. 274); ovules mostly indefinite, and amphitropal. Fruit a capsule opening by valves or a lid. Seeds pelate, albuminous; embryo straight, transverse. The plants abound in cold and in northern regions. Sedative, diaphoretic, and even drastic purgative plants are found in this order. Under the genus *Primula* are included the various species of Primrose, Cowslip, Oxlip, and Auricula.

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**SUB-CLASS IV.—MONOCILAMYDEAE OR APETALE.**

1. **Angiospermae.**

a. **Spermogonae.—Having true Seeds with a Dicotyledonous Embryo.**

Nat. Ord. 171.—**Nyctaginaceae**, the Marvel of Peru order.—Herbs or shrubs, with opposite leaves, and involu- crate, often showy flowers. Perianth tubular and funnel- shaped, the limb plaited, coloured, and separating from the hardened base, which incloses the one-celled utricular fruit, and appears to be incorporated with it. Stamens hypogy- nous, 1-20. Embryo coiled round mealy albumen. Na- tives of warm regions. Their roots are purgative, as seen in the case of *Mirabilis Jalapa*.

Nat. Ord. 172.—**Amaranthaceae**, the Amaranth order. —Herbs or shrubs, with opposite or alternate, exstipulate leaves, and capitate or spiked, bracteated coloured flowers, which are occasionally unsexual. Perianth of 3-5 scarious sepals. Stamens 5, hypogynous, distinct or monadelphous; anthers often 1-celled. In other respects resembling Che- nopodiaceae. Most common within the tropics. They have mucilaginous properties. Some are used as pot-herbs, and many of them are cultivated on account of their dry, persistent, and finely coloured bracts and perianth. Ama- ranths are known in gardens by the name of Princes Feather (*Amaranthus hypochondriacus*) and Love-lies-bleeding (*A. caudatus*). *Celosia cristata*, the Cockscumb, has astringent properties.

Nat. Ord. 173.—**Chenopodiaceae**, the Goosefoot order (Fig. 178).—Herbs or undershrubs, with exstipulate, alter- nate, and occasionally opposite leaves, and small herbaceous, often unsexual flowers. Perianth divided deeply, some- times tubular at the base, persistent. Stamens inserted into the base of the perianth, and opposite to its divisions. Ovary free, 1-celled, with a single ovule attached to its base. Fruit a utricle or achene, sometimes succulent. Em- bryo coiled round mealy albumen, or spiral without albumen. Inconspicuous plants, found in waste places in various parts of the world, chiefly in extra-tropical regions. Many of the plants of this order are used as pot-herbs, for instance, Spinage, Garden Orach, and Beet. Soda is supplied by some of the species of *Salicornia* and *Salosa* growing on the sea-shore. Anthelmintic and antispasmodic properties are also met with in the order.

Nat. Ord. 174.—**Basellaceae**, the Basella order.—A small order of climbing, herbaceous, and shrubby tropical plants, closely allied to Chenopodiaceae, and differing chiefly in their coloured double perianth, and in their stamens being attached to its sides. Some species of *Basella* are used as Spinage. *Melocca tuberosa* has a tuberous root, which is used in Peru as a substitute for the Potato.

Nat. Ord. 175.—**Scleranthaceae**, the Scleranthus or Knawel order.—Inconspicuous weeds, often included among the Illecebraceae, but differing from that order in their apetalous flowers, exstipulate leaves, hardened tube of the perianth inclosing the 1-celled fruit, and perigynous stamens. They seem to be more nearly allied to Chenopodiaceae. They occur in barren places in various parts of the world.

Nat. Ord. 176.—**Phytolaccaceae**, the Poke-weed order.—Herbs or undershrubs, with alternate, exstipulate, often dotted leaves, and racemose flowers. Perianth of 4-5 leaves, often petaloid. Stamens hypogynous or nearly so, indefinite, or 4-5 and then alternate with the divisions of the perianth. Ovary of 1 or many united one-seeded carpels; styles and stigmas distinct. Fruit either succulent or dry. Embryo curved round mealy albumen. Many of the plants are American. They have acrid, emetic, and purgative qualities. The berries of *Phytolacca decandra*, Poke or Pocan, yield a deep purple juice. Its root is emetic, and is used in rheumatic and syphilitic pains. The young shoots are eaten as Asparagus. *Gyrostemon*, a genus with unisexual flowers, is considered as a type of an allied order, *Gyrostemonaceae*.

Nat. Ord. 177.—**Petiveriaceae**, the Petiveria order.—A small order of plants separated from Phytolaccaceae on account of their stipulate leaves, exalbunious seeds, straight embryo, and convolute cotyledons. Tropical American plants. They have acid properties and an alliaceous odour.

Nat. Ord. 178.—**Polygonaceae**, the Buckwheat order (Figs. 527, 528).—Herbs, rarely shrubs, with alternate leaves, ochrace stipules, and occasionally unisexual flowers. Perianth often coloured. Stamens definite, and inserted into the base of the Perianth. Ovary formed of 3 carpels, 1-celled, containing a single orthotropical ovule. Fruit a triangular nut, often covered by the perianth (Fig. 529). Embryo usually on one side of mealy albumen. Generally distributed both in cold and warm climates. Acid, astringent, and purgative qualities are met with in the plants of this order. *Fagopyrum esculentum*, and other species, are cultivated as Buckwheat. *Polygonum Bistorta* has a twisted rhizome, which is used as an astringent. Various species of *Rheum* yield the different kinds of Rhubarb. *R. palmatum* is generally said to be the plant which supplies Russian or Turkey Rhubarb.

Nat. Ord. 179.—**Begoniaceae**, the Begonia order.—Herbs or succulent undershrubs, with alternate oblique stipulate leaves, and cymose, pink, unisexual flowers. Perianth superior, coloured, with 4 divisions in the male flower, and 5-8 in the female. Stamens 2, distinct or united; anthers collected into a head. Ovary winged, 3-celled, with 3 placentas meeting in the axis. Fruit capsular, winged, 3-celled. Seeds 2, exalbunious, reticulated. Found in the East and West Indies, and in South America. They are said to have bitter and astringent qualities. *Begonias* receive the name of Elephant's-ear from the appearance of their oblique leaves. Their succulent stalks are sometimes used like Rhubarb.

Nat. Ord. 180.—**Lauraceae**, the Laurel order (Figs. 529, 530).—Trees with exstipulate, usually alternate, dotted leaves. Perianth 4-cleft, or 6-cleft in 2 rows. Stamens often 8-12, the 3 or 4 innermost being abortive staminodia, and the outer fertile; filaments sometimes bearing glands, anthers 2-4-celled, opening by recurved valves. Ovary superior, 1-celled, with 1 or 2 pendulous ovules. Fruit a berry or drupe; pedicel often thickened; seed solitary, exalbunious; embryo with large cotyledons. Tropical aromatic and fragrant plants, yielding fixed as well as volatile oils and camphor. Some have tonic and febrifugal barks; others supply edible fruits. The timber of some of the plants is valuable. *Camphora officinarum*, a tree found in China and Japan, supplies camphor. *Cinnamomum zeylanicum*, is the Cinnamon-tree, the bark of which constitutes the Cinnamon of commerce. *Laurus nobilis*, Sweet-bay, yields a concrete green oil, called Oil of Bays. Its branches were used to crown the victors in the ancient games. *Nectandra Rodiei* (*N. leucantha*, var. N. ab. E.), yields the Bebeeru-bark, which contains an antiperiodic alkaloid Bebeeria. Its wood is called Green-heart, and is used in ship-building.

Nat. Ord. 181.—**Atherospermaceae**, the Plume-Nutmeg order.—Trees, with opposite exstipulate leaves, and bracteated unisexual flowers. Perianth tubular, divided at the top into segments, in 2 rows, the inner partly petaloid. Stamens numerous, inserted in the bottom of the perianth; filaments with scales at their base; anthers with valvar dehiscence. In the female flowers, there are often abortive stamens in the form of scales. Carpel numerous, each having a single erect anatropical ovule. Fruit achenes, inclosed in the tube of the perianth, having persistent feathery styles. Seed solitary, erect; embryo minute in the base of fleshy albumen. Fragrant plants from Australia and Chili.

Nat. Ord. 182.—**Myristicaceae**, the Nutmeg order.*—Tropical trees, with alternate, exstipulate leaves, and uni-sexual flowers. Perianth 3-4-cleft, valvate. Stamens 3-12, distinct or monadelphous; anthers extrorse, often united. In the female flowers, the perianth is deciduous. Carpels 1 or many, each with a single erect anatropical ovule. Fruit succulent, 2-valved. Albumen ruminate. Some regard this order as an apetalous unisexual form of Annonaceae. Natives of the tropical parts of India and America. The plants of this order are acid and aromatic. Their bark yields a red juice. *Myristica moschata* is the Nutmeg-tree of the Moluccas. The fruit is drupaceous and dehisces, so as to display the scarlet mace, which consists of a reticulated arilode covering the shell in which the seed or Nutmeg is inclosed.

Nat. Ord. 183.—**Monimiaceae**, the Monimia order.—Trees or shrubs, with opposite, exstipulate leaves, and unisexual flowers, resembling Atherospermaceae, from which they differ chiefly in the anthers dehiscing longitudinally, in the ovule being pendulous, and in the want of feathery styles to the fruit. The plants are chiefly South American, and possess aromatic qualities.

Nat. Ord. 184.—**Proteaceae**, the Protea order.—Shrubs or small trees, with hard, dry, exstipulate leaves. Perianth Botany.

divided into 4, valvate. Stamens 4, placed on the segments of the perianth. Ovary of one superior carpel, containing 1 or more ovules; fruit dehiscent or closed. Seed exalbuminous; embryo straight. Natives of Australia and the Cape of Good Hope chiefly. *Leucadendron argenteum* is the Witteboom or Silver-tree of the Cape. *Protea grandiflora* is called Wagenboom.

Nat. Ord. 185.—ELEOAGNACEAE, the Oleaster order.—Trees or shrubs, usually lepidote, with exstipulate leaves, and unisexual, rarely hermaphrodite, flowers. Male flowers in the axil of scales; perianth of 2-4 leaves, sometimes united; stamens 3, 4, or 8. In the ♀ and ♂ flowers, perianth tubular, with a fleshy disk. Ovary free, 1-celled, with a single ascending ovule. Fruit a crustaceous achene, inclosed in the succulent perianth. Found chiefly in the northern hemisphere. Many are cultivated for their silvery scaly foliage. The scales are beautiful microscopic objects (Fig. 53). *Hippophae rhamnoides*, Sea Buckthorn, is a spiny plant which thrives on the sea-shore. *Eleocharis erythropoda*, small-leaved Oleaster, bears clusters of red edible berries, mottled with scales.

Nat. Ord. 186.—PENAEACEAE, the Penaea order.—Shrubs, with opposite exstipulate leaves. Perianth inferior, bracteated, salver-shaped, limb 4-lobed. Stamens 4 or 8, inserted on the perianth. Ovary 4-celled, with 4 appendaged stigmas. Fruit a 4-celled capsule. Seed exalbuminous; embryo with minute cotyledons. Evergreens, found at the Cape of Good Hope. Some yield a gum-resin called Sarocol.

Nat. Ord. 187.—THYMELEACEAE, the Mezereon order.—Shrubby plants, with stipulate leaves, and ♀ rarely ♀♂ flowers. Perianth coloured, tubular, with a 4-5-lobed imbricate limb. Stamens often twice as many as the lobes of the perianth, and inserted on its tube. Carpel solitary, superior, with a single pendulous ovule. Fruit nut-like or drupaceous. Seed with or without albumen; embryo straight. Natives both of cold and of warm climates in various parts of the world. The plants of this order possess acrid, irritant, and occasionally narcotic qualities. The bark of many of them is tough and tenacious, so as to be used for cordage. *Daphne cannabina* has a fibrous inner bark, which is used for ropes and for the manufacture of paper. *Lagetta lutea* is called Lace-bark tree, on account of the beautiful meshes of its inner bark.

Nat. Ord. 188.—AQUILARIACEAE, the Aquariella order.—Trees, with exstipulate leaves. Perianth tubular, with a 4-5-lobed imbricate limb. Stamens usually 8-10, inserted into the throat of the perianth. Ovary superior, 2-celled, with 2 suspended ovules. Fruit a 2-valved capsule, or succulent. Seeds exalbuminous. Natives of the tropical parts of Asia. Some of the plants yield resinous matter, which is used as a stimulant.

Nat. Ord. 189.—SAMYDACEAE, the Samyda order.—Trees or shrubs, with alternate, stipulate, usually dotted leaves. Perianth 4-5-parted; aestivation imbricate. Stamens inserted into the tube of the perianth, 2, 3, or 4 times as many as its divisions, some of them occasionally sterile; filaments united. Ovary superior, 1-celled, with numerous ovules. Fruit, a leathery, 1-celled, 3-5-valved capsule. Seeds albuminous, arillate, attached to parietal placentas. Tropical, chiefly American plants, with astringent bark and leaves.

Nat. Ord. 190.—SANTALACEAE, the Sandalwood order.—Trees, shrubs, or herbs, with alternate, entire, exstipulate leaves, and small flowers, sometimes ♀♂. Perianth adherent, 4-5-cleft, valvate. Stamens 4-5, inserted into the throat of the perianth opposite its segments. Ovary 1-celled; ovules 1-4; placentation central. Fruit monospermal, dry, or succulent. Seed albuminous. Found in Europe, Asia, America, and Australia. Some of the species are astringent, others yield edible fruit. The wood is in some instances fragrant, and the bark is tough and tenacious. *Santalum album*, a Malabar tree, from 25 to 30 feet high, produces Sandal-wood, which is used as a perfume in China, and in India as an astringent.

Nat. Ord. 191.—ARISTOLOCHIACEAE, the Birthwort order (Fig. 531).—Herbs or climbing shrubby plants, with alternate leaves, solitary or clustered brown or greenish coloured ♀ flowers, and wood arranged in separable wedges. Perianth tubular (Fig. 383), adherent, valvate. Stamens 6-12, epigynous, distinct or adherent to the style and stigmas (Fig. 248). Ovary 3-6-celled; ovules ♀♂; stigmas radiating. Fruit a 3-6-celled polyspermal capsule or berry. Seeds albuminous; embryo minute. Found in various parts of the world, but abundant in the tropical parts of South America. Birthworts have pungent, aromatic, stimulant, and tonic properties. Some have been celebrated for their effects on the uterus, others as antidotes for snake-bites. The root of various species of *Aristolochia* have been used as emmenagogues. The root of *A. serpentaria*, Virginian Snake-root, formerly of repute in typhus fever, and also in cases of snake-bite, is a valuable stomachic.

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**Fig. 531.**

Diagram of the flower of *Asarum europaeum*, Asarabacca, showing three divisions of the perianth, nine stamens in three rows, and a 3-loculed ovary.

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**Fig. 532.**

Flowers of *Neptunia distillatoria*, the Pitcher-plant. The racemose flowers are seen with the operculate ascidia at the end of the leaves.

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Nat. Ord. 192.—NEPENTHACEAE, the Pitcher-plant order (Fig. 532).—Herbacous or suffruticose plants, with alternate leaves, having calyptrimorphous ascidia at their extremities (Fig. 140), wood in separable wedges, and race-mace diocious flowers. Perianth inferior, 4-leaved, imbricate. Stamens columnar, with anthers collected into a head. Ovary superior, tetragonal, 4-celled; ovules ♀♂; ascending. Fruit a 4-celled, 4-valved capsule, loculicidal. Seeds with a loose testa, albuminous. Found in marshy ground in the East Indies and China.

Nat. Ord. 193.—DATISCACEAE, the Datisca order.—Herbs or trees, with alternate exstipulate leaves, and ♀♂ flowers. Perianth, 3-4 divided, adherent to the ovary. Stamens 3-7, ovary unilocular, with 3-4 polyspermous parietal placentas. Fruit a 1-celled capsule opening at the apex. Seeds strophiolate, exalbuminous. The plants are scattered over various parts of the world, chiefly in the northern hemisphere. Bitter and purgative properties are met with in the order. Some yield fibres.

Nat. Ord. 194.—EMBETTACEAE, the Crowberry order.—Shrubs, with heath-like, evergreen, exstipulate leaves, and small axillary unisexual flowers. Perianth of 4-6 hypogynous persistent scales, the innermost sometimes petaloid and united. Stamens 2-3, alternate with the inner row of scales. Ovary free, on a fleshy disk, 2-9-celled; ovules solitary. Fruit fleshy, with 2-9 nuclei. Seed solitary, ascending; embryo with an inferior radicle. A small group, allied to Euphorbiaceae, and distinguished chiefly by its ascending seeds and inferior radicle. Natives chiefly of the northern parts of Europe and America. Their leaves... Botany.

and fruit are often subacid. *Euphorbia nigra*, Crowberry, has black watery fruit.

Nat. Ord. 195.—*Euphorbiaceae*, the Spurge-wort order.*

Trees, shrubs, or herbs, with opposite or alternate, often stipulate leaves, and involucrate (Fig. 533), unisexual, sometimes, achlamydeous flowers (Fig. 209). Perianth, when present, inferior, lobed, with glandular, scaly, or petaloid appendages. Stamens definite or separate (Fig. 246), or united in one or more bundles (Fig. 251). Ovary 1, 2, or 3 or more celled; ovules 1 or 2, suspended. Fruit usually trilococcus (Fig. 534), the carpels separating with elasticity, sometimes fleshy and indehiscent. Seeds albuminous, often arillate. Embryo with a superior radicle. Lindley considers this a dichlamydeous order, and as becoming monoclamydeous or achlamydeous by abortion. The plants abound in equinoctial America. Some are found in North America, Africa, India, and Europe. The plants of the order are generally acid and poisonous, abounding in a milky juice. Starchy matter is procured from many of the species, as well as oils and caoutchouc. *Croton Eleuteria* produces a tonic bark known by the name of Cascara. The seeds of *C. Tiglium* yield, by expression, Croton-oil, which is a drastic purgative in doses of one or two drops. *Euphorbia Lathyris*, Caper-purge, has been used as a purgative. *E. officinarum* is the source of the purgative resin called Euphorbium, *Jambu Mantha* is the Cassava or Manioc plant. *Oldfieldia africana* is the tree which supplies the African Teak. The seeds of *Ricinus communis* yield Castor-oil by expression.

Nat. Ord. 196.—*Scrophulariaceae*, the Scop order.—Trees, with alternate stipulate leaves and unisexual flowers, resembling Euphorbiaceae, and differing chiefly in being amenitious. The perianth is 4, 5, or 6-leaved; stamens 2-5; ovary 2-celled, ovules in pairs; seeds arillate, often buried in hairs. Natives of India.

Nat. Ord. 197.—*Callitrichaceae*, the Starwort order.—Aquatic herbs, with opposite leaves, and minute axillary unisexual achlamydeous flowers. Stamen 1, rarely 2; anther reniform, 1-celled. Ovary solitary, tetragonal, 4-celled; ovules solitary in each cell; styles 2. Fruit 4-celled, 4-seeded, indehiscent. Seeds peltate, albuminous; embryo with a superior radicle. Natives of still waters in Europe and North America.

Nat. Ord. 198.—*Ceratophyllaceae*, the Hornwort order.—Aquatic herbs, with verticillate leaves and monoeious flowers. Perianth inferior, 10-12-clot; anthers sessile, 12-20; ovary 1-celled, with 1 pendulous ovule. Fruit an achene; seed exalbuminous; embryo with an inferior radicle. Found in ditches in various parts of the world.

Nat. Ord. 199.—*Urticaceae*, the Nettle and Hemp order (Figs. 535, 536).—Trees, shrubs, or herbs, with watery juice and alternate stipulate leaves, often covered with asperities or stinging hairs (Fig. 48). Flowers unisexual, rarely 2, scattered or collected into heads or catkins. Perianth divided; stamens definite, opposite the lobes of the perianth, and inserted into its base; filaments sometimes curved and elastic (Fig. 378); ovary superior, 1-celled, with a solitary ovule; fruit indehiscent, with a single seed. Embryo straight, hooked, or spiral, with or without albumen; radicle superior. Natives chiefly of temperate regions. Some of the plants have caustic juice connected with stinging hairs; others yield valuable fibres. Occasionally narcotic qualities are present. *Bohmeria nivea* supplies the fibres whence Chinese grass-cloth is made. *Cannabis sativa*, the common Hemp plant. An Indian variety, *C. indica*, possesses powerful narcotic qualities. *Humulus Lupulus*, the Hop, is cultivated on account of its bitter principle, Lupulin, which exists in the resinous scales (Fig. 54) surrounding the fruit.

Nat. Ord. 200.—*Artocarpaceae*, the Bread-fruit* and *Plate CXXXIII.

Mulberry order (Figs. 537, 538)—Trees or shrubs, with a milky juice, and alternate lobed leaves, having large stipules. The flowers are 2, and are collected into dense heads or catkins. The plants are considered by many as a section of Urticaceae, from which they differ chiefly in being lactescent, in their fruit being a sorosis (Fig. 326), or syconus (Fig. 157). Perianth divided (Fig. 537), often wanting; ovary 1-celled; ovules erect or pendulous. Fruit polygynous or anthocarpous, consisting of achenes immersed in the persistent fleshy perianth (Fig. 538), or situated upon (Fig. 156) or within large fleshy receptacles (Fig. 157). Seeds albuminous or exalbuminous; embryo straight or hooked. The plants of this order supply, in many instances, edible fruits; their milky juice often abounds in caoutchouc, and, in some instances, is bland and nutritious, while their inner bark supplies fibres. Bitter, tonic, as well as acid and poisonous properties, are found in the order. *Antiaris toxicaria* is a large tree, whence the Javanese poison called Upas-Antiar is obtained, and which owes its activity to a peculiar principle Antiarin. *Artocarpus incisa*, the Bread-fruit tree (Fig. 326), has large pinnatifid leaves, while *A. integrifolia*, the Jack-fruit, has undivided leaves. *Gadactodendron utile*, the Cow-tree of South America, has a nutritive milky juice. *Dorstenia Contrayerva*, and other species (Fig. 156), have a stimulant, tonic, and diaphoretic rhizome. *Ficus Carica*, the common Fig (Fig. 157), is used as a laxative and as a cataplasm. *Urostigma (Ficus) elasticum*, and other species, supply caoutchouc abundantly. *U. indicum* (benghalense) is the Banyan-tree of India (Fig. 65).

Nat. Ord. 201.—*Ulmaceae*, the Elm order.—Trees or shrubs, with scabrous, alternate, stipuled leaves, and 2 or 3 flowers in loose clusters. Perianth inferior, membranous, campanulate, irregular. Stamens definite, attached to the base of the perianth. Ovary 1-2-celled; ovules solitary, pendulous; stigmas 2. Fruit 1 or 2-celled, indehiscent, dry, or drupaceous. Seed solitary, without or with little albumen. Bitter and astringent properties exist in the bark and fruit of some of the plants of this order. Many are valuable timber-trees. Botany.

Nat. Ord. 202.—Stilaginaceae, the Stilago order.—Trees or shrubs, with alternate, stipuled leaves, and minute flowers in scaly spikes. They are allied to Urticaceae, and are chiefly distinguished by their large disk and vertical antherine cells, opening transversely, and having a fleshy connective. Their fruit is drupaceous, and seed suspended and albuminous. Natives of the East Indies and of Madagascar.

Nat. Ord. 203.—Lacistemaee, the Lacistema order.—Shrubs, with alternate, simple stipuled leaves, and 5 or 6 flowers in axillary catkins. Perianth free, divided, with a large bract. Stamens 1, hypogynous; connective separating antherine cells, which open transversely. Disk often fleshy. Ovary 1-celled; placentas parietal. Fruit a 1-celled 2-3-valved capsule, loculicidal. Seeds suspended, arilate, albuminous. Natives of the tropical woods of America.

Nat. Ord. 204.—Podostemonaceae, the River-weed order.—Submersed aquatic herbs, with capillary or minute leaves, which are often densely imbricated. They have the aspect of Mosses or Liverworts. Flowers usually 5. Perianth imperfect or 0, sometimes of 3 parts, with a spathe. Stamens 1, or many, hypogynous. Ovary 2-3-celled; placentas parietal or axile. Fruit a 2-3-valved capsule. Seeds numerous, exalbuminous; embryo orthotropial. Chiefly natives of South America. Some of the species are used for food.

Nat. Ord. 205.—Chloranthaceae, the Chloranthus order.—Herbs or undershrubs, with jointed stems, opposite simple leaves, sheathing petioles, interpetiolar stipules, and spiked 5 or 5 flowers. Scaly bract, no perianth. Stamens definite, lateral, 1 or more; anthers 1-2-celled, with a fleshy connective. Ovary 1-celled; ovule orthotropial. Fruit drupaceous. Seed pendulous; embryo minute, at the apex of fleshy albumen; no vitellus. Natives of the warm regions of India and America chiefly. They have aromatic and stimulant properties. The leaves of Chloranthus inconspicuous are sometimes used to perfume tea.

Nat. Ord. 206.—Saururaceae, the Lizard-tail order.—Marshy herbs, with alternate, stipuled leaves, 5 spiked flowers, each supported on a scale. Perianth 0. Stamens 3-6, hypogynous, club-shaped, persistent. Ovaries 3-4, distinct or united. Ovules few, orthotropial. Fruit of 4 achenes, or a 3-4-celled capsule. Embryo in a vitellus, outside mealy albumen, at the apex of the seed. Natives of North America, China, and Northern India.

Nat. Ord. 207.—Piperaceae, the Pepper order (Figs. 539 and 540).—Shrubs or herbs with jointed stems, usually opposite or verticillate leaves, stipules sometimes present, flowers 5 in spikes, each supported on a bract, no perianth. Stamens 2 or more; ovary free, 1-celled; ovule 1, erect, orthotropial. Fruit somewhat fleshy, indehiscent, 1-celled, 1-seeded. Seed erect; embryo in a vitellus or fleshy sac outside the albumen, and at the apex of the seed. The stems of Pepper have a peculiar arrangement of the woody matter in wedges and not in concentric zones. Natives of tropical regions, especially in America and Asia. The plants of this order are pungent and aromatic, owing to the presence of an acid resin, an oil, and a crystalline matter called Piperin. Some possess narcotic qualities, others are astringent. Chavica Roxburghii, and other species (Fig. 539), produce Long-pepper, which is the dried female spikes. Cubeba officinalis, and other species, produce the aromatic pungent fruit called Cubeb. Piper nigrum (Fig. 540) is a climbing East Indian plant, the dried unripe fruit of which constitutes Black Pepper.

Nat. Ord. 208.—Myricaceae, the Gale order (Fig. 541).—Amentiferous shrubs or small trees, with resinous glands, alternate leaves, and unisexual flowers. Perianth 0. Stamens 2-3, usually in the axil of a bract; anthers 2-4-celled. Ovary 1-celled, with hypogynous scales; ovule solitary, orthotropial; stigmas 2. Fruit drupaceous, often covered with wax, and with adherent fleshy scales. Seed solitary, erect, exalbuminous; embryo with superior radicle. Found both in temperate and in tropical countries. The plants have aromatic, tonic, and astringent properties. Tannic and benzoic acids, as well as wax, resin, and oil, are procured from different species. The berries of Myrica cerifera, Wax Myrtle or Candleberry (Fig. 541), furnish a greenish-coloured wax when put into hot water.

Nat. Ord. 209.—Salicaceae, the Willow order (Figs. 542 to 544).—Amentiferous trees or shrubs (Fig. 167), with alternate, simple, stipuled leaves, sometimes with petiolar glands, and 5 flowers. Perianth 0, or cup-like. Stamens 2-30. Ovary superior, 1-celled; ovules numerous, erect, attached to the bottom of the cell, or to the base of 2 parietal placentas; stigmas 2. Fruit leathery, 1-celled, 2-valved, polyspermal. Seeds covered with basal silky hairs, exalbuminous; embryo erect, with an inferior radicle. Chiefly found in northern regions; some grow on the high mountains of South America, others in antarctic regions. The plants of this order are useful timber trees, and they are employed for various economical purposes. Their bark is tonic and astringent. The downy matter surrounding the seeds is used for stuffing cushions, and for making paper. The bark of Salix alba, S. Helix, S. purpurea, S. fragilis, S. caprea, S. pentandra, and many other species, contains a bitter tonic principle called Salicin.

Nat. Ord. 210.—Altingiaceae or Balsamiflora, the Liquidambar order.—Amentiferous unisexual trees, with alternate, stipuled leaves, and involucrate catkins. Anthers 2, nearly sessile, with a few minute scales. Ovaries 2- celled, collected into a round mass, each with a few scales; styles 2; ovules 2, amphitropous. Fruit, consisting of 2-celled capsules, inclosed in scales, and forming a sort of cone. Seeds winged, peltate, alburninous; embryo inverted, radicle superior. Natives of the warmer parts of India and America; also found in the Levant. Fragrant and balsamic properties are met with in this order. The bark of some of the plants is bitter.

Nat. Ord. 211.—Betulaceae, the Birch order (Fig. 545).—Amentiferous trees or shrubs, with alternate, simple, stipulate, often feather-veined leaves, and unisexual flowers, which have small scales in place of a perianth. Stamens opposite the scales. Ovary 2-celled; ovules 1 in each cell, pendulous, anatropous; stigmas 2. Fruit dry, indehiscent, 1-celled, 1-seeded. Seed exalbuminous; radicle superior. In Alnus there is a 4-leaved membranous perianth. The plants of this order are usually timber trees, such as the Birch and Alder, with deciduous leaves, chiefly found in northern and cold regions. Their bark is tonic and astringent.

Nat. Ord. 212.—Corylaceae or Cupuliferae, the Hazel and Oak order (Fig. 546).—Amentiferous trees or shrubs, with simple, alternate, stipulate, often feather-veined leaves, and monoecious flowers (Fig. 546). Barren flowers in catkins. Stamens 5-20, inserted in the base of scales, or of a membranous valvate perianth. Fertile flowers aggregate (Fig. 546, Q), or on a spike. Ovary, with several cells, crowned by the remains of an adherent perianth inclosed in an involucre or cupula (Fig. 299). Ovules in pairs or solitary, pendulous or peltate; stigmas several. Fruit a glans (Fig. 300); seed solitary, exalbuminous. The plants abound in the forests of temperate regions in the form of Oaks, Hazels, Beeches, and Chestnuts. The plants of this order afford valuable timber and edible seeds. Astringency also prevails in a marked degree in the bark.

Nat. Ord. 213.—Casuarinaceae, the Beefwood order.—Leafless trees, with pendulous, jointed, striated, sheathed branches, and spikes or heads of unisexual flowers proceeding from bracts. Barren flowers in spikes, and whorled round a jointed rachis. Perianth 2-leaved, with 2 alternating bracts. Stamen 1, carrying up the united 2 leaves of the perianth in the form of a lid. Fertile flowers, capitate, without a jointed rachis, and naked. Ovary 1-celled; ovules 1 or 2, orthotropous; styles 2. Fruit, winged achenes, combined into a bracteated cone. Seed exalbuminous; episperm with spiral cells; radicle superior. Tropical or subtropical plants, having the aspect of Equisetums. They abound in Australia. Their wood is hard and heavy, and on account of its colour is called Beefwood. The bark of some of the species of Casuarina is tonic and astringent.

Nat. Ord. 214.—Platanaceae, the Plane order (Fig. 547).—Amentiferous trees or shrubs, with alternate, deciduous, palmate, or toothed, stipulate leaves, and unisexual naked flowers in globose catkins (Fig. 547). Barren flowers. Stamens single, mixed with scales. Fertile flowers. Ovary 1-celled; style thick and subulate. Ovules 1-2, orthotropous, suspended. Nuts clavate, with a persistent style. Seeds usually solitary and albuminous; radicle inferior. Natives of the Levant and North America chiefly. The species of Platanus are fine trees, but their timber is not durable.

Nat. Ord. 215.—Juglandaceae, the Walnut order (Fig. 548).—Trees, with alternate, pinnate, stipuled leaves, and unisexual flowers. 5: Amentiferous. Perianth 2-3-parted, with a scaly bract. Stamens 3 or more. 9: In terminal clusters or in loose racemes, with distinct or united bracts. Perianth adherent, 3-5-divided. Ovary 2-4-celled at the base, unicellular at the apex. Ovule solitary, orthotropous, and erect; style 1 or 2. Fruit a tryma, endocarp stony and often 2-valved. Seed exalbuminous, 2-4-lobed at the base, and partly divided by partial dissepiments. Natives chiefly of North America. Some are found in the East Indies, Persia, and the Caucasus. The plants are fine trees with edible oily seeds and an acrid bark. Purgative qualities are found in some of the species. Carya illinoiensis, the common Hickory-tree, produces an eatable nut. Juglans regia is the Walnut-tree (Fig. 548).

Nat. Ord. 216.—Garryaceae, the Garrya order.—Shrubs with opposite, exstipulate leaves, and amentiferous unisexual flowers, surrounded by united bracts. 5: Perianth of 4 leaves, alternating with 4 stamens. 9: Perianth adherent, bidentate. Ovary 1-celled; styles 2; ovules 2, pendulous with long cords. Fruit a 2-seeded berry. Embryo minute in the base of fleshy albumen. The wood is not arranged in circles, and there is an absence of dotted vessels. Natives chiefly of the temperate parts of America. b. Sporogone or Rhizanthus.—Having Spore-like Seeds with an Acotyledonous Embryo.

Nat. Ord. 217.—Rafflesiaceae, the Rafflesia order (Fig. 549).—Stemless and leafless parasites, consisting only of ♀ or ♂ flowers growing on the branches of trees. Perianth superior, with a 3-parted limb, thickened processes or calli, either distinct or united into a ring, being attached to the throat of the tube. The essential organs are combined in a column (synema) which adheres to the tube of the perianth. Anthers 2-celled, either distinct and opening by vertical apertures, or combined together, so as to become a multicellular mass opening by a common pore. Ovary 1-celled, placentas parietal. Fruit indehiscent. Seeds ♂; embryo cellular, undivided. East Indian and South American plants, parasitic on species of Cissus and on some Leguminosae.

Nat. Ord. 218.—Cytinaceae, the Cistus-rape order.—Root-parasites, having ♀ or ♂ flowers, which are either solitary and stemless, or proceed from bracts arising from a scaly stalk. Perianth has a tubular form, and a 3-6-lobed limb. Anthers sessile, 2-celled, opening longitudinally. Ovary inferior, 1-celled; placentas parietal. Fruit containing pulp. Seeds ♂, immersed in pulp, and with a leathery covering; embryo undivided. Natives of the south of Europe and the Cape of Good Hope. Parasitical on the roots of Cistus, and on those of some succulent plants.

Nat. Ord. 219.—Balanophoraceae, the Balanophora order.—Leafless root-parasites, with tubers or rhizomes, whence proceed naked or scaly peduncles, bearing heads of unisexual bracteated flowers, mixed with filaments. ♀: Flowers generally white. Perianth tubular, 3-5-lobed or entire. Stamens 3-5, rarely 1; anthers free or united into a multicellular mass. ♀: Perianth having its tube closely investing the ovary, and its limb 0 or bilabiately; rarely 6-leaved. Ovary 1-celled; ovule pendulous, cellular nucleus; styles 1-2. Fruit somewhat drupaceous. Seed solitary, albuminous; embryo undivided. Parasitical on the roots of various Dicotyledons, and abounding on the mountains of tropical countries, especially the Andes and Himalaya.

2. Gymnospermae or Gymnogene.

Nat. Ord. 220.—Coniferae or Pinacae, the Coniferous or Pine order (Figs. 550 to 553).—Resinous trees or shrubs, with disk-bearing woody tissue (Fig. 550), linear, acerose or lanceolate, parallel-veined leaves, sometimes clustered and having a membranous sheath at the base (Fig. 551); flowers unisexual and achlamydeous. Male flowers in deciduous catkins, each consisting of 1 stamen or of several united; anthers 2 or many-celled, dehiscing longitudinally, often crested above (Fig. 552). Female flowers in cones; scales arising from the axil of membranous bracts supplying the place of ovaries; no style nor stigma; ovules naked, 1, 2, or several, at the base of each scale, with a large micropyle at the apex (Fig. 296). Fruit a cone formed of hardened scales, sometimes with the addition of bracts also, which either disappear, or become enlarged and lobed. Seed with a hard crustaceous spermoderm, sometimes winged (Figs. 553 and 328); embryo in fleshy oily albumen, sometimes poly-

cotyledonous (Fig. 341); radicle having no definite boundary, but losing itself among the lax cells of the albumen near the apex of the seed. Conifers are found in various parts of the world, both in cold and in warm climates. They are most abundant in temperate regions, both in the northern and southern hemispheres. In the former they occur in the form of Pines, Spruces, Larches, Cedars, and Junipers, while in the latter we meet with species of Araucaria, Eudoxa, and Dammara. The two following divisions have been adopted.—Sub-order 1: Abietinae; the Fir tribe; ovules inverted, pollen oval, or curved (Fig. 267). Sub-order 2: Cupressinae; the Cypress tribe; ovules erect, pollen spheroidal, cone occasionally succulent, forming a galbulus. Conifers supply valuable timber, and yield resin, oil, pitch, and turpentine of various kinds. *Abies balsamea*, the Balm of Gilead Fir, and *A. canadensis*, Hemlock Spruce, yield Canada Balsam. *Cedrus Libani*, is the Cedar of Lebanon; *C. Deodara*, the Deodar, is a noble Himalayan Cedar, which some have thought to be a variety of the Cedar of Lebanon. *Dammara australis*, is the Kaurie or Cowdie Pine of New Zealand, which attains a height of 200 feet, and supplies valuable timber for masts, as well as a hard useful resin; *D. orientalis* yields the Dammar resin of India. *Eudoxa excelsa* is the famous Norfolk Island Pine, which grows to the height of 181-224 feet, and the wood of which is very valuable. The species of *Juniperus* have a succulent cone called galbulus.

Nat. Ord. 221.—Taxaceae, the Yew order (Figs. 554 and 555). Trees or shrubs, having narrow, evergreen, alternate, or distichous leaves which are either veinless or have a forked venation. Closely allied to Coniferae, and generally included as a section of the order, but differing in not producing true cones. They have monadelphous stamens (Fig. 554); solitary, naked ovules, and their seed is supported on, or inclosed by, a succulent cup-shaped receptacle (Fig. 555). They are natives of temperate regions, and abound in Asiatic countries. They Botany.

are found also in Europe, New Zealand, and the Cape of Good Hope. Like the Conifers they yield valuable and durable timber, along with resinous and astringent matter. Some are poisonous. The seeds of *Taxus baccata*, the common Yew, are narcotic-acrid.

Nat. Ord. 222.—*Gnetaceae*, the Jointed-Fir order.—Small trees or creeping shrubs, not resinous, with jointed stems and branches, and opposite, reticulated, sometimes scaly leaves. They are closely allied to Coniferae and Taxaceae, and are chiefly distinguished by the want of true cones, by the male flowers having a 1-leaved perianth, by the anthers being 1-celled and porose, by a third ovular covering next the nucleus being protruded through the foramen in a style-like manner, and by their long, twisted embryonic suspensor. The episperm is succulent. Natives of temperate as well as warm regions in Europe, Asia, and South America. The seeds of several of the species are eaten. Within the succulent episperm of *Gnetum urens*, stinging needle-like cells exist.

Nat. Ord. 223.—*Cycadaceae*, the Cycas order (Fig. 556).—Small palm-like trees or shrubs, with unbranched stems, occasionally dichotomous, marked with leaf-scars, and having large medullary rays, along with pitted tissue. Leaves pinnate, and usually circinate in vernation. Flowers & & and achlamydeous. Males in cones, the scales bearing clusters of 1-celled anthers on their lower surface. Females consisting of ovules on the edge of altered leaves, or placed below or at the base of scales. Seeds either hard, or having a soft, spongy sperm, sometimes polyembryonous; embryo hanging by a long suspensor in a cavity of fleshy or mealy albumen; cotyledons unequal. Natives chiefly of the tropical and temperate regions of America and Asia. Cycads have a mucilaginous juice, in which there is often much starch, which is used for food. *Cycas revoluta* (Fig. 556), a Japan species, has starchy matter in its stem, which is collected and eaten like Sago. *C. circinalis*, in the Moluccas, yields a similar kind of false Sago. Species of *Encephalartos* supply what is called Caffre-bread.

*Note.*—Among Thalamitiferous Exogens, the following orders contain Monochlamydeous or Achlamydeous species:—Ranunculaceae 1, Menispermaceae 6, Papaveraceae 13, Flacourtiaceae 18, Caricaceae 24, Stemonaceae 31, Butteniaceae 32, Tiliaceae 33, Malpighiaceae 45, Geraniaceae 54, Rutaceae 63, Xanthoxylaceae 64. Among Calycifloral Exogens, the following orders contain Monochlamydeous or Achlamydeous species:—Celastraceae 68, Rhamnaceae 71, Amygdalaceae 73, Leguminosae 75, Rosaceae sect. Sanguisorbeae 77, Lythraceae 79, Compositae 82, Myrtaceae 86, Haloragaceae 91, Cucurbitaceae 93, Passifloraceae 96, Portulacaceae 99, Ilecebraceae 100, Tetramoniaceae 103, Saxifragaceae 107, Cannoniaceae 109, Loranthaceae 113. Among Corollifloral Exogens, the following orders contain Monochlamydeous or Achlamydeous species:—Oleaceae 140, Primulaceae 168.

CLASS II.—MONOCOTYLEDONES, ENDOGENE, OR AMPHIBRYA.

SUB-CLASS I.—DICOTYLOGENAE.

Endogens having Net-veined Leaves, which usually disarticulate with the Stem. Woody Matter of the Rhizome disposed in a circular wedge-like manner.

Nat. Ord. 224.—*Dioscoreaceae*, the Yam order.—Twining shrubs, with epigean or hypogean tubers, usually alternate leaves, and small bracteated, unisexual flowers growing in spikes. Perianth 6-cleft, in 2 rows, herbaceous, adherent. Stamens 6, inserted into the base of the perianth. Ovary inferior, 3-celled; ovules 1-2, suspended; style trifid. Fruit compressed, 3-celled, 2 cells often abortive, sometimes fleshy. Seeds albuminous; embryo in a cavity. Chiefly found in tropical countries. *Tamus* grows in temperate regions. Acridity prevails in the order, but is often associated with a large amount of starch. Various species of *Dioscorea*, such as *D. sativa*, *D. alata*, and *D. aculeata*, produces edible tubers, which are known by the name of Yams, and are used like potatoes. *Tamus communis*, Black Bryony, has an acrid purgative and emetic root.

Nat. Ord. 225.—*Smilacaceae*, the Sarsaparilla order (Fig. 557).—Herbs or shrubby plants, often climbing, with petiolate leaves jointed to the stem, and hermaphrodite or unisexual flowers. Perianth 6-parted. Stamens 6, perigynous or hypogynous. Ovary 3-celled; stigmas 3; ovules orthotropal. Fruit a few or many-seeded berry. Seed albuminous. Natives of temperate and tropical regions. The plants of the order have demulcent, mucilaginous, and diuretic properties. *Smilax* embraces the various species of Sarsaparilla, the roots of which are used medicinally as tonics and alteratives. *S. officinalis* supplies Jamaica Sarsaparilla, and according to Seemann, Lisbon or Brazilian, Guatemala, and Rio Paraguay Sarza.

Nat. Ord. 226.—*Trilliaceae*, the Trillium order.—Herbs with tubers or rhizomes, verticillate leaves, and large terminal flowers. Perianth of 6 or eight parts, in 2 rows, the inner sometimes coloured. Stamens 6, 8, or 10, with apical processes. Ovary superior, 3-5 celled; placenta axile; styles 3-5. Fruit succulent, 3-5-celled. Seeds x, albuminous. Natives of the temperate parts of Europe, Asia, and North America. The properties of the order are acrid, narcotic, and emetic.

Nat. Ord. 227.—*Roxburghiaceae*, the Roxburghia order.—Twining shrubs, with large, solitary flowers, allied to Trilliaceae, and distinguished chiefly by their 1-celled, 2-valved fruit, with a basal placenta. Perianth 4-leaved, coloured. Stamens 4, hypogynous. Ovules anatropal. Natives of the hot parts of India.

Nat. Ord. 228.—*Philiseae*, the Philisia order.—A small order, nearly allied to the last, from which it differs in its trimerous symmetry, parietal placentas, and orthotropal ovules. The plants are found in Chili, and seem to have properties like Smilax.

SUB-CLASS II.—PETALOIDEAE OR FLORIDEAE.

1.—*Epigyne*.—Perianth adherent, Ovary inferior, Flowers usually Hermaphrodite.

Nat. Ord. 229.—*Hydrocharitaceae*, the Frog-bit order.—Aquatic plants, with spathaceous, & or unisexual flowers. Perianth of 6 leaves, the three inner petaloid. Ovary 1-celled, or sparingly 3-9-celled; stigmas 3-9; placentas parietal. Fruit dry or fleshy, indehiscent; seeds exalbuminous; embryo straight, orthotropal. This order ought probably to be placed among the unisexual plants, and close to Najadaceae. Its perianth, however, differs from that of the plants in the division Incompletae. Found chiefly in Botany. Europe, Asia, and North America. Movements in the cells are seen under the microscope (Fig. 23). *Anacaris Alsinastus* has become naturalized in many parts of Britain, and grows so rapidly as to fill up water-courses. *Vallisneria* (Fig. 22) is remarkable for its mode of impregnation.

Nat. Ord. 230.—ORCHIDACEAE, the Orchis order (Figs. 558 and 559).—Terrestrial or epiphytic herbs or shrubs, with fibrous or tuberous roots (Fig. 69), a short stem or a pseudo-bulb (Fig. 70), entire, often sheathing leaves, and hermaphrodite showy flowers. Perianth of 6 segments, in two rows, mostly coloured, one, the lowest (so situated from the twisting of the ovary) generally differing in form from the rest, and often spurred; it is called the labellum or lip, and has sometimes 3 marked portions,—the lowest being the hypochilium, the middle the mesochilium, and the upper the epichilium. By adhesion or abortion, the parts of the perianth are sometimes reduced to 5 or 3. Essential organs united on a common column or gynostemium. Stamens 3, the 2 outer, sometimes the central one, being abortive; anthers 2-4-8-celled; pollen powdery, or adhering in masses called pollinia (Fig. 265), attached to the rostellum by a naked or saccate gland. Ovary 1-celled, with 3 parietal placentas, stigma a viscid space in front of the column. Fruit usually a 3-valved capsule, which often opens by 6 portions, owing to the midribs of the valves separating. Seeds ∞, exalbuminous, with a loose reticulated epipperm; embryo solid and fleshy. This order is well distinguished by its peculiar gamandrous flowers, labellum, and pollinia. Fragrant, aromatic, tonic, and mucilaginous properties are met with among Orchids. The roots of some of the terrestrial species contain much bassorin, and they constitute the nutritious substance called Salep. Blue colouring matter, like indigo, is met with in the leaves and flowers of some species. *Orchis mascula*, and other species, such as *O. Morio* and *O. papilionacea*, yield Salep. *Vanilla planifolia* and *aromatica* yield the fragrant Vanilla, used in confectionery and in the preparation of Chocolate.

Nat. Ord. 231.—APOTASTACEAE, the Apostasia order.—A small order of herbaceous plants closely allied to Orchids, from which they differ chiefly in their regular flowers, 3-celled loculicidal fruit, and in the style being free from the stamens throughout a considerable part of its length. The column is short, and is formed by the filaments along with the lower part of the style. Natives of the hot forests of India.

Nat. Ord. 232.—BURMANNIAE, the Burmannia order.—A small order of herbaceous plants, with tufted, radical, acute leaves, or none, and a slender stem bearing alternate bract-like leaflets. They resemble Orchids in their minute seeds with a loose reticulated epipperm, their parietal placentas, and their solid embryo; and are chiefly distinguished by their regular tubular flowers, stamens 3 or 6, dehiscing transversely, free, and inserted into the tube of the coloured perianth. Natives chiefly of tropical regions in Asia, Africa, and America.

Nat. Ord. 233.—ZINGIBERACEAE OR SCITAMINEAE, the Ginger order (Fig. 560).—Herbs, with a rhizome, simple sheathing leaves, the veins parallel and diverging from a midrib, and flowers arising from membranous spathes. Perianth tubular, irregular, and in 3 rows, the outer (calyx) 3-lobed, the middle (corolla) and inner (staminodes) each 3-parted, with a segment differing from the rest. Stamens 3, free, the two lateral abortive; anthers 2-celled. Fruit a 3-celled capsule or berry. Seeds numerous, albuminous; embryo in a vitellus. Nearly all tropical plants; abundant in the East Indies. The plants of this order have aromatic, stimulating properties, and are used as condiments, and as stomachic remedies. Their flowers are often very gaudy, and their bracts are sometimes finely coloured. The capsules of *Acanthus Cardamomum* are called round Cardamoms; those of *A. angustifolium* are the Madagascar Cardamoms. *Curcuma longa* has a yellow coloured rhizome, the branches of which constitute Turmeric. *Zingiber officinale* (Fig. 560) has an aromatic rhizome which constitutes Ginger.

Nat. Ord. 234.—MARANTACEAE OR CANNACEAE, the Arrow-root order.—Herbaceous plants closely allied to Zingiberaceae, from which they differ chiefly in the want of aroma, in having one of the lateral stamens fertile (the other two being abortive), in the single stamen having a petaloid filament, which bears a 1-celled anther (the other antherine lobe being sterile), in the style being petaloid, and in the embryo not being contained in a vitellus (Fig. 420). Natives of the tropics of America, Africa, and Asia. Amylaceous qualities prevail in this order, and starch is prepared from many of the species. The corms or rhizomes of *Canna indica*, and *C. edulis*, and *C. Achiras*, all yield starch, some of which is known as Tous-les-mois. *Maranta arundinacea* yields Arrow-root.

Nat. Ord. 235.—MUSAECAE, the Banana order (Fig. 561).—Plants with underground stems, their petioles forming a spurious aerial stem (Fig. 86), their leaves having parallel veins diverging from a midrib, and their flowers being bracteated. Perianth irregular and petaloid, 6-parted in 2 rows. Stamens 6, inserted on the perianth. Anthers linear, 2-celled, often crested. Fruit a 3-celled loculicidal capsule, or succulent and indehiscent (Fig. 561). Seeds albuminous; embryo orthotropial. Tropical plants, which are valuable as regards food, clothing, and other domestic purposes. They yield much nutritive food, as well as useful fibres. *Mus a paradisiaca*, the Plantain, and *M. sapientum*, the Banana, supply well-known fruits, which serve for the food of the inhabitants of many tropical countries. *M. textile* produces Manilla Hemp, which is used in manufacture.

Nat. Ord. 236.—IRIDACEAE, the Iris order (Figs. 562 and 563).—Herbs with corms, rhizomes, or fibrous roots, and mostly equitant leaves, and spathaceous flowers. Perianth 6-divided in 2 rows, sometimes irregular. Stamens 3, inserted at the base of the outer row of the perianth; anthers innate, extrorse. Style dividing into 3 petaloid stigmaticiferous portions (Fig. 563). Capsule 3-celled, 3-valved, loculicidal. Seeds with hard albumen. Found in various temperate and warm parts of the world. The order has its maximum at the Cape of Good Hope. Acrid, purgative, and emetic properties are met with in some plants of the

order. Some are fragrant and aromatic; others supply starch and materials for dyeing. The dried stigmatic processes of *Crocus sativus* constitute Saffron. The rhizome of *Iris florentina*, the Florence Iris, is the aromatic Orris-root, which has the odour of Violets.

Nat. Ord. 237.—AMARYLLIDACEAE, the Amaryllis order (Fig. 564).—Bulbous, sometimes fibrous-rooted plants, with ensiform leaves, and showy flowers, which are mostly spatheaceous and on scapes (Fig. 149). Perianth coloured, limb 6-parted or 6-cleft, sometimes with a corona, as in *Narcissus* (Fig. 149). Stamens 6, inserted at the bottom of the segments, sometimes united by a membrane, as in *Pancratium*; anthers introrse. Stigma 3-lobed. Fruit a 3-celled, 3-valved, loculicidal capsule, with many seeds; or a berry with 1-3 seeds, spermoderm not crustaceous; albumen fleshy; embryo with radicle next the hilum. Natives of various parts of the world, but attaining their maximum at the Cape of Good Hope. Many Amaryllids display poisonous properties. Some are emetic and purgative, and some yield useful fibres. The bulbs of the Snowdrop and Snowflake are said to be emetic. *Agave americana*, American Aloe, is used in America for the manufacture of an intoxicating beverage. Its fibres constitute Pita Flax, and are sometimes made into paper.

Nat. Ord. 238.—HIPPOXIDACEAE, the Hypoxis order.—Herbs, with tuberous or fibrous roots, linear, dry, often hairy leaves, and trimorose flowers in scapes. Closely allied to Amaryllids, and differing chiefly in their strophiolate seeds, and embryo with the radicle remote from the hilum. Natives of warm regions.

Nat. Ord. 239.—HEMORRHOIDEAE, the Blood-root order.—Perennial plants, with fibrous roots, ensiform equitant leaves, and woolly hairs or scarf on their stems and flowers. Perianth tubular, 6-divided. Stamens 3, opposite the segments, or 6; anthers introrse. Ovary 3-celled, sometimes 1-celled; style and stigma simple. Fruit usually capsular and valvular, covered by the withered perianth. Embryo in cartilaginous albumen, radicle remote from the hilum. Natives of America, the Cape, and New Holland. Bitterness is found in some of the plants of the order (*Aletis*). Their roots are sometimes nutritious, and many of them are of a red colour, whence the name of the order.

Nat. Ord. 240.—TACCACEAE, the Tacca order.—Perennial herbs, with tuberous roots, radical curve-veined leaves, and flowers in scapes. Perianth tubular, 6-divided. Stamens 6, inserted in the base of the segments; filaments petaloid; another below the points of the filaments. Styles 3. Fruit baccate, 1-celled, or half 3-celled. Albumen fleshy. Acrid plants found in the warmest parts of India and Africa, as well as in the South Sea Islands. The tubers of *Tacca pinnatifida*, and other species, yield starch.

Nat. Ord. 241.—BROMELIACEAE, the Pine-apple order.—American and chiefly tropical plants, with rigid, channelled, often scurfy and spiny leaves, and showy flowers. Outer perianth 3-parted, persistent; inner of 3 withering leaves. Stamens 6, inserted in the tube of the perianth; anthers introrse. Style single. Fruit capsular or succulent, 3-celled, many-seeded. Embryo minute, in the base of mealy albumen. Many of the plants grow in an epiphytic manner, and are called air-plants. This is the case especially with *Tillandsias*. Some of the species have anthelmintic properties. Some supply edible fruit, gum, colouring matter, and valuable fibres. The fibres of *Ananassa sativa*, the Pine-apple, are used in manufacture.

2. HYPOGyne.—Perianth free, Ovary superior, Flowers usually Hermaphrodite.

Nat. Ord. 242.—LILIACEAE, the Lily order (Figs. 565 and 566).—Herbs, shrubs, or trees, with bulbs (Fig. 111), corms, rhizomes (Fig. 73), or fibrous roots, simple, sheathing, or clasping leaves, and regular flowers. Perianth coloured, of 6 leaves (Fig 566), or 6-cleft. Stamens 6, inserted in the perianth; anthers introrse. Ovary 3-celled (Fig. 279); style 1; stigma simple or 3-lobed. Fruit trilocular, capsular, or succulent. Seeds in 1 or 2 rows, sometimes in pairs or solitary; albumen fleshy. Natives both of temperate and tropical regions. In the latter we meet with arborescent species, such as the Dragon-trees, and with succulent species, as Aloes. In temperate climes we have species of Tulip, Lily, Hemerocallis, Convallaria, Fritillary, Hyacinth, and Star of Bethlehem. The properties of the order are various. Some of the plants are used as emetics and purgatives, while others are stimulant and diaphoretic. Some yield resinous and astringent matter, while others supply valuable materials for manufactures. *Aloe* is the genus which supplies the drug called Aloes. It is the inspissated juice of various species, such as *A. spicata*, *vulgaris*, *socotrina*, *indica*, and *purpurea*. *Phormium tenax* supplies New Zealand flax. *Urginea Scilla*, known as *Scilla* or *Squilla maritima*, a Mediterranean sand plant, has an acrid bulb which, when dried, Botany.

constitutes the common Squill of the shops. It is used as an emetic, expectorant, and diuretic.

Nat. Ord. 243.—Melanthiaceae or Colchicaceae, the Colchicum order (Fig. 567).—Herbs, with bulbs, corms (Fig. 74), or fasciculated roots, and white, green, or purple flowers, which are sometimes polygamous. Perianth petaloid, of 6 leaves, which are either separate, or united below into a tube. Stamens 6, anthers extrorse. Ovary 3-celled; style 3-parted; capsule 3-valved, septicidal (Colchicum), sometimes loculicidal (Uvularia). Seeds with a membranous episperm, and dense, fleshy albumen. Generally distributed over the world, but most abundant in northern countries. The plants of this order have acid, emetic, purgative, and sometimes narcotic properties. They are all more or less poisonous, and nearly all seem to contain the alkaloid called Veratrine. Asparagus officinalis, is the chief source of the Cevadilla or Saladilla seeds, which contain veratrine, and are used in neuralgic and rheumatic affections. The corms and ripe seeds of Colchicum autumnale, the Meadow Saffron, contain an alkaloid Colchicine, and are prescribed in gout and rheumatism.

Nat. Ord. 244.—Gilliesiaceae, the Gilliesia order.—Bulbous herbs, with grass-like leaves, and umbellate, spatheaceous flowers. Perianth of 2 portions,—outer petaloid and herbaceous, of 6 leaves, called by Lindley bracts; inner minute, either a single lobe or urceolate and 5-toothed. The latter is by some considered an abortive staminal row. Stamens 6, sometimes 3 sterile. Capsule 3-celled, 3-valved, loculicidal, polyspermous. Episperm black and brittle; embryo curved; albumen fleshy. Chilian plants.

Nat. Ord. 245.—Pontederiaceae, the Pontederia order.—Aquatic plants, with leaves sheathing at the base, petioles occasionally dilated, and spathaceous flowers, either solitary or in spikes. Perianth coloured, tubular, 6-parted, irregular, persistent. Stamens 6 or 3, perigynous; anthers introrse. Capsule sometimes slightly adherent, 3-celled, 3-valved, loculicidal. Seeds numerous; placenta central; albumen mealy. Natives of America, India, and Africa.

Nat. Ord. 246.—Xyridaceae, the Xyris order.—Swampy rush-like plants, with ensiform or filiform radical leaves sheathing at the base. Flowers in scaly heads. Perianth of 6 parts, 3 outer glumaceous. Stamens 6, 3 fertile inserted on the inner perianth. Anthers extrorse. Ovary 1-celled; placentas parietal; ovules orthotropical. Capsule 1-celled, 3-valved, polyspermous. Albumen fleshy; embryo remote from the hilum. Tropical plants. Some species of Xyris have been used in cutaneous affections.

Nat. Ord. 247.—Philydraceae, the Water-wort order.—Plants allied closely to Xyrids, and differing chiefly in the want of an outer perianth, in the inner perianth being 2-leaved, in having 3 stamens, 2 of which are abortive, and in the embryo being large in the axis of the albumen. The flowers have spathaceous bracts; the roots are fibrous, the stem simple, leafy, and often woolly, and the leaves sheathing at the base. Natives of New Holland and China.

Nat. Ord. 248.—Commeliniaceae, the Spider-wort order.—Herbs, with flat leaves, usually sheathing at the base. Outer perianth of 3 parts, herbaceous; inner also 3, coloured, sometimes cohering. Stamens 6, or fewer, hypogynous. Anthers introrse; ovary 3-celled; placenta central; style 1. Capsule 2-3-celled, 2-3-valved, loculicidal. Seeds with a linear hilum; embryo pulley-shaped, in a cavity of the albumen, remote from the hilum. In Tradescantia the filaments are provided with jointed hairs, which show rotation in their cells. The rhizomes of some species of Commelina are amylaceous and edible.

Nat. Ord. 249.—Mayacaceae, the Mayaca order.—Moss-like plants, with narrow leaves, resembling Spider-worts, but differing in their 1-celled anthers, carpels opposite the inner divisions of the perianth, 1-celled ovary and capsule, and parietal placentas. Natives of America.

Nat. Ord. 250.—Juncaceae, the Rush order (Figs. 568 and 569).—Herbs, with fasciculate or fibrous roots, fistular or flat and grooved leaves, and glumaceous sometimes peltate flowers in clusters, cymes, or heads. Perianth dry, greenish or brownish, 6-parted (Fig. 569). Stamens 6 or 3, perigynous; anthers introrse. Ovary 1 or 3-celled; ovules 1, 3, or many in each cell; style 1; stigma often 3. Fruit a 3-valved loculicidal capsule, or monospermal and indehiscent. Seeds with a thin spermoderm, which often becomes gelatinous when moistened; albumen fleshy; embryo minute. Natives chiefly of cold and temperate regions. The leaves are used to form matting and the bottoms of chairs, and the pith for the wicks of candles.

Nat. Ord. 251.—Palmae, the Palm order (Fig. 570 to 573).—Arborescent plants, with a simple (Fig. 570), some-

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Fig. 570. Phoenix dactylifera, the Date Palm.

--- Fig. 571. Diagram of the flower of Chamaerops, Fan-palm, showing six divisions of the perianth and six stamens.

--- Fig. 572. Diagram of the flower of Chamaerops, showing six divisions of the perianth in two rows, and three cells of the ovary.

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Fig. 573. Section of the fruit of the Coco-nut, showing the central cavity in the albumen, and the embryo lying in a separate cavity which is remote from the hilum. with a central cavity; embryo in a particular cavity remote from the hilum (Fig. 573), its cotyledon often becoming enlarged during germination, and filling the central cavity. Chiefly tropical plants, requiring a mean temperature of 78°-2 to 81°-5 F. Some, however, extend to temperate regions.

*Chamaerops humilis*, the dwarf Fan-palm, is found native in the south of Europe, and *C. Palmetto* grows in the milder parts of North America. Some have slender, reed-like stems, others attain a considerable diameter. Some have a low caudex, or a subterranean stem, while others have an erect trunk 190 feet high. Palms yield numerous important products, and they are applied to a great many uses. They supply starch, sugar, oil, wax, and edible fruits; their buds are eaten like vegetables; their leaves form coverings for habitations, and materials for manuscripts, the reticulum makes coarse cloth, and the saccharine juice is sometimes fermented, so as to form a spirit called arrack, or palm-wine called toddy. *Areca Catechu* furnishes the Betel-nut, used all over the East as a masticatory. *Cocos nucifera*, the Cocoanut Palm is perhaps put to a greater number of uses than any other Palm, both as regards food, luxuries, clothing, habitations, and utensils. *Elais guineensis* supplies the solid Palm-oil. *Metroxylon laevis*, a native of Borneo and Sumatra, is one of the sources of the starchy matter called Sago. *Phytelephas macrocarpa*, a Palm of the Magdalena River district, is called the Vegetable Ivory-Palm, because the hard horny albumen of its seed is used like ivory. *Sagus Rumphii* is the Sago-Palm of Malacca.

Nat. Ord. 252.—**Alemaceae**, the Water-plantain order.—Floating or marsh plants, with a creeping rhizome, narrow or broad leaves, and flowers in umbels, racemes, or panicles. Perianth of 6 pieces; outer 3 herbaceous; inner 3 petaloid. Ovaries several, 1-celled; ovules solitary, or 2 superposed. Fruit indehiscent. Seeds exalbuminous; embryo like a horse-shoe, undivided. Natives chiefly of northern countries. The fleshy rhizomes of *Alisma* and *Sagittaria* are edible.

Nat. Ord. 253.—**Juncaginaceae**, the Arrow-grass order.—Marsh plants, with narrow radical leaves, and ♀ flowers in spikes or racemes. Perianth greenish. Stamens 6; anthers extrorse. Carpels 3-6, united, or distinct; ovules 1 or 2, erect. Fruit dry, 1-2-seeded. Albumen 0; embryo straight, with a lateral cleft. A small order of plants found in cold and temperate regions.

Nat. Ord. 254.—**Butomaceae**, the Flowering-rush order.—Aquatics, with very cellular leaves, often milky, and umbellate handsome flowers. Perianth of 6 pieces, 3 inner petaloid. Stamens definite or ∞. Ovaries 3-6 or more, distinct or united; ovules ∞. Fruit follicles, distinct or united. Seeds ∞, attached to a reticulated placenta, spread over the whole inner surface of the fruit; albumen 0. Natives chiefly of northern countries.

3. **Incomplete.**—Flowers incomplete, generally Unisexual, without a proper Perianth, or with a few Verticillate Scales.

Nat. Ord. 255.—**Pandanaceae**, the Screw-pine order.—Trees or bushes, often branching dichotomously, or in a candelabra-like manner, having adventitious roots (Fig. 66), leaves imbricated, linear-lanceolate or pinnate or fan-shaped, and spiny; and flowers unisexual or polygamous, spatheaceous, covering a spadix completely. Perianth 0, or a few scales. Stamens numerous; anthers 2-4-celled. Ovaries 1-celled, collected into parcels; stigmas sessile; ovules solitary or numerous. Fruit either 1-seeded fibrous nuts, or many-seeded berries. Albumen fleshy; embryo minute, without a lateral slit. Natives of tropical regions, and abundant in insular situations.

Nat. Ord. 256.—**Typhaceae**, the Bulrush order.—Herbs, growing in marshes or ditches, having stems without nodes, rigid, ensiform leaves, and monocious flowers on a spadix, without a spathe. Perianth 3 or more scales, or a bundle of hairs. Stamens 1-6, distinct or monadelphous; anthers innate. Ovary solitary, 1-celled; ovule solitary, pendulous. Fruit dry or spongy, indehiscent, 1-celled, angular by pressure. Seed solitary, pendulous, with a membranous spermaderm adhering to the pericarp. Embryo in the axis of mealy albumen, straight with a lateral cleft; radicle next the hilum. Most abundant in northern countries. Starch is a product of the rhizomes of many species of *Typha*, and the pollen, which is very abundant, is inflammable, and is also used for food.

Nat. Ord. 257.—**Araceae**, the Arum order.*—Herbs or Plate shrubby plants, sometimes climbing, often with corms; leaves sheathing at the base, convolute in aestivation, sometimes compound, and usually with branching veins; flowers monocious, on a spadix (Fig. 165), mostly with a spathe. Perianth 0. Stamens definite or ∞; anthers extrorse, 1 or 2-celled or more. Ovary with 1 or more cells. Fruit succulent; seeds pulpy; embryo in the axis of fleshy and mealy albumen, with a lateral cleft. Abundant in tropical climates; rare in cold or temperate regions. Acridity prevails in the order, and many of the plants are irritant poisons. The corms sometimes supply starch, which is separated from the acrid matter by washing. *Arum maculatum*, Cuckow-pint, or Wake-Robin, has an amylaceous acid corm. The starch used to be separated in large quantities at Weymouth and in the island of Portland, and sold under the name of Portland Sago. *Colocasia esculenta*, and other species, have edible corms, which are called Cocoes and Eddoes in the West Indies.

Nat. Ord. 258.—**Orontiaceae** or **Acoraceae**, the Orontium or Sweet-flag order.—Herbs with broad, occasionally ensiform leaves, and spadiceous flowers inclosed by a spathe. They are usually associated with Araceae, from which they differ in their hermaphrodite flowers, and in having frequently a perianth consisting of 4-8 scales. Lindley, on account of their ♀ flowers, places them near Juncaceae. Natives both of tropical and cold regions. Acridity is met with in this order, which also contains nutritious, bitter, and aromatic plants. *Acorus Calamus*, common Sweet-Sedge, has an agreeable odour, and has been used as a stimulant, tonic, and antispasmodic. Its starchy matter is associated with a fragrant oil, and is used as hair-powder.

Nat. Ord. 259.—**Pistiaceae** or **Lemnaceae**, the Duckweed order (Fig. 674).—Floating plants with lenticular or lobed leaves or fronds, bearing 1 or 2 monocious flowers inclosed in a spathe, but with no perianth. Stamens definite, often monadelphous. Ovary 1-celled; ovules 1 or more, erect or horizontal. Fruit indehiscent or membranous, or bursting transversely, or baccate, 1 or more-seeded. Seeds with a thick ribbed episperm and an indurated micropyle; embryo in the axis of fleshy albumen, with a lateral cleft, or at the apex of the nucleus. Natives both of cool and of warm regions. *Lemna* form a green covering of pools in Britain. *Pistia Stratiotes*, Water-lettuce, floats in the ponds of warm countries.

Nat. Ord. 260.—**Naiadaceae** or **Potamogetonaceae**, the Naias or Pondweed order.—Plants of fresh or salt water, with cellular leaves and stems, and inconspicuous spiked flowers, which are sometimes hermaphrodite. Perianth of 1-4 scaly pieces or 0. Stamens definite, hypogynous. Ovary free, of one or more carpels, 1-celled; ovule solitary, erect or pendulous, rarely 3 and erect. Style simple, or 2-3-cleft. Fruit indehiscent, dry, 1-celled, and usually 1-seeded; albumen 0; embryo with a lateral cleft. What is called the perianth in Potamogeton, and a few other allied genera, is considered by some as composed of bracts, bearing unisexual flowers. If that is the true view, then this order will not include any ♀ plants. Natives of temperate and warm climates. Some species are stypic, others yield edible roots, and a few, as *Zostera*, are used for stuffing cushions and beds.

Nat. Ord. 261.—**Thurniaceae**, the Triuris order.—A small tropical order of cellular, unisexual plants, allied to Najadaceae, but distinguished in part by their peculiar seed, which consists of a hard striated integument, containing an embryo in the form of a multicellular nucleus.

Nat. Ord. 262.—**Restiaceae**, the Restio order.—Herbs or undershrubs, with narrow leaves or 0, naked or sheathed stalks, and flowers in bracteated heads or spikes, generally ♀♂; glumaceous bracts 2-6, sometimes 0. Stamens 2-3; anthers usually 1-celled. Ovary 1 or more-celled; ovules, one in each cell, pendulous. Fruit a capsule or nut. Embryo lenticular, outside the albumen. Natives chiefly of South America, Australia, and South Africa. Their wiry stems are used for baskets and brooms, and for thatching.

Nat. Ord. 263.—**Eriocaulonaceae**, the Pipewort order.—Marsh plants, with minute, unisexual flowers, allied to the last order, and differing principally in their capitate inflorescence, 2-celled anthers, ovary surrounded by a 2-3-toothed membranous tube, and seeds with rows of hairs. The species abound in South America, and they are also found in Australia and North America. *Eriocaulon septangulare*, jointed Pipewort, is the only species found in Britain. It is met with in Skye and Galway.

Nat. Ord. 264.—**Desvauxiaceae**, the Bristlewort order.—Small herbs, like species of Scirpus, having setaceous leaves, flowers glumaceous in a spathe, distinguished from Restiaceae principally in having separate ovaries attached to a common axis, and fruit consisting of utricles opening longitudinally. They inhabit the South Sea Islands and New Holland.

**SUB-CLASS III. GLUMIFERE.**

Nat. Ord. 265.—**Cyperaceae**, the Sedge order (Figs. 575 to 577).—Grass-like, cespitose plants, have solid, usually unjointed, and frequently angular stems, leaves with entire sheaths, and ♀♂ or ♀♂ flowers, each with a solitary bract or glume (Fig. 575), imbricated on a common axis, so as to form a spikelet. The lowermost glumes are often empty. Perianth 0, or existing in the female flowers in the form of a membranaceous covering called perigynium (Fig. 235). Stamens hypogynous, definite, varying from 1 to 12, most commonly 3; anthers innate, 2-celled. Ovary superior, often surrounded by hypogynous bristles called setae (Fig. 576); ovule 1, erect; style single, 2-3-cleft; stigmas 2-3. Fruit a crustaceous or bony achene. Embryo lenticular, in the base of fleshy or mealy albumen (Fig. 577). Generally distributed all over the world, and growing abundantly in moist situations. Some of the Sedges are diaphoretic and demulcent, others are bitter, stomachic, and astringent. The creeping stems of *Carex arenaria* are used as a substitute for Sarsaparilla.

Nat. Ord. 266.—**Gramineae**, the Grass order (Figs. 578 and 579).—Herbaceous plants, with round, usually hollow, jointed stems; narrow, alternate leaves, having a splitting sheath and often a ligule at its summit (Fig. 134); hermaphrodite or monococious, or polygamous flowers, either solitary or arranged in spiked or panicle locustae (Fig. 165). The flowers are considered as composed of a series of bracts; the outer, called glumes (Figs. 150 and 231), alternate, often unequal, usually 2, sometimes 1, rarely 0; the next, called pales or lemmae (paleae or glumellae), usually 2, alternate (Figs. 232 and 233), the lower or outer ones being simple, the upper or inner having 2 dorsal or lateral ribs, and supposed to be formed by 2 pales united; sometimes 1 or both are wanting. The glumes inclose either one flower, as in Fox-tail grass, or more flowers, as in Wheat (Fig. 165), and among the flowers there are frequently abortive florets (Fig. 150). Stamens hypogynous, 1-6, usually 3 (Fig. 234); anthers versatile. Ovary superior, 1-celled, with 2 (rarely 1 or 0) hypogynous scales called lodicules (Figs. 234, sq); ovule 1; styles 2 or 3, rarely united; stigmas often feathery (Fig. 234). Fruit a caryopsis. Embryo lenticular, external, lying on one side, at the base of farnaceous albumen (Fig. 579). Germination endorhizal (Fig. 419). Grasses are widely distributed, and are found in all quarters of the globe. Schaw conjectures that they constitute 1-22d of all known plants. They are usually social plants, forming herbage in temperate regions, and sometimes becoming arborescent (50 or 60 feet high) in tropical countries. This is perhaps the most important order in the vegetable kingdom, as supplying food for man and animals. To it belong the cultivated grains, Wheat, Oats, Barley, Rye, *Plate Maize*, and Millet. Most of these have been so long under constant cultivation that their native state is unknown. The properties of the order are nutritive in a marked degree. Some yield fragrant oils, others produce sugar. The fragrant odour given out by *Anthoxanthum*, and other grasses used for hay, has been attributed to benzoic acid. *Lotus*. temulentum, Darnel-grass, has been said to be narcotic and poisonous, but this has not been fully proved. *Andropogon Schenanthus*, Lemon-grass, and *A. Calamus aromaticus*, yield a fragrant oil. *Bambusa arundinacea*, the Bamboo, attains a great height, and in hothouses in Britain it has sometimes grown at the rate of a foot or more per day. *Saccharum officinarum*, is the Sugar-cane.

II.—CRYPTOGAMÆ, ACOTYLEDONEÆ, OR FLOWERLESS PLANTS.

CLASS III.—ACOTYLEDONES OR ACO-THALLOGENÆ.

SUB-CLASS I.—ACOGENE, ACORRYA, OR CORMOGENE.¹

Nat. Ord. 267.—Filices, the Fern order (Figs. 580 to 582).—Leafy plants, the leaves, or more properly fronds, being circinate vernation (Fig. 100), and arising from a rhizome (Fig. 580), or from a hollow arborecent trunk (Fig. 87), having the acrogenous structure. The fronds bear on the veins of their lower surface (Figs 580 and 581), or along their margins, sporangia, which open in various ways in order to discharge minute spores. The supposed organs of reproduction, called antheridia and archegonia (Figs. 396 and 398) are seen on the young frond, when first developed from the spore in the form of a prothallus.

The following divisions have been adopted:—Sub-order 1. Polypodiaceae, the Polypody tribe (Fig. 580); Sporangia, in variously-shaped clusters, called sori, on the back or margins of the fronds, each sporangium having a vertical, incomplete ring (*annulus*), or a horizontal complete one, which, when mature, straightens so as to open the spore-case transversely, or irregularly, and thus discharge the spores (Fig. 554). The sori are covered by an indusium or involucre (Fig. 581), or by the reflexed margins of the frond.—Sub-order 2. Osmundaceæ, the Flowering-fern tribe (Fig. 582); Sporangia dorsal, or clustered on the margin of a transformed frond, with a terminal or dorsal ring, more or less complete, reticulated, and opening vertically.—Sub-order 3. Ophioglossaceæ, the Adder's-tongue tribe; Sporangia in a spike-like form, sessile on the margin of a contracted frond, without reticulation or a ring (exannulate), 2-valved; fronds with straight vernation.—Sub-order 4. Danaeaceæ, the Danaea tribe; Sporangia dorsal, combined in masses, exannulate, splitting irregularly by a central cleft. A moist insular climate is that best adapted for ferns in general. Ferns characterize the flora of New Zealand. Some Ferns are used medicinally as anthelmintics, while others are demulcent and astringent. The rhizomes of several species, are used as food in Australia, the Sandwich Islands, and India. *Adiantum Capillus Veneris*, true Maiden-hair, has been used in the preparation of Syrup of Capillaire. *Lastrea Filix-mas* is an effectual vermifuge in cases of Tape-worm.

Nat. Ord. 268.—Marsileaceæ or Rhizocarpaceæ, the Pepperwort or Rhizocarp order.—Aquatic plants, with creeping stems, bearing leaves, which are usually divided into 3 or more cuneate portions, and have a circinate vernation. The fructification is produced at the base of the leafstalks, and consists of sporocarps or involucres inclosing clustered organs (Fig. 360), which consist of antheridial and pistillidian cells. The germinating body has an oval form, and occasionally a mammilla on one side, whence roots and leaves proceed. Found in ditches in various parts of the world, chiefly in temperate regions.

Nat. Ord. 269.—Lycophodiaceæ, the Club-moss order.—Plants with creeping stems or corms, which produce leafy branches (Fig. 357), somewhat resembling Mosses. The leaves are small, sessile, and imbricated or verticillate. The fructification occurs in the axil of leaves, and often in a spike-like form (Fig. 357, f), and consists of kidney-shaped, 2-valved cases, which contain antheridial or spermatozoidal cells (Fig. 358), and roundish or four-sided bodies, called oophoridia, opening by 2 valves, and containing 4 large spores (Fig. 359). In the interior of the latter a pro-embryo is developed, in which archegonia are produced (Fig. 360), and thereafter impregnation gives rise to the germinating body. Natives both of cold and warm climates, but abounding in the tropics, and especially in insular situations. Some of the plants have emetic and purgative properties. The powdery matter contained in their fructification is inflammable, and is known as Lycopode powder or vegetable brimstone.

Nat. Ord. 270.—Equisetaceæ, the Horse-tail order (Fig. 355).—Cryptogams having rhizomes or underground stems, bearing hollow, striated, siliceous branches, which are jointed and have membranous sheaths at the articulations. The place of leaves is supplied by green-coloured branchlets, which are sometimes verticillate. The fructification consists of cone-like bodies bearing peluate polygonal scales, under which are spore-cases opening inwards by a longitudinal fissure, and inclosing spores with 2 hygroscopic club-shaped elaters (Fig. 9). The plants have a coniferoid prothallus, and on it antheridial and archegonial cells are developed. Found in ditches and rivers in all parts of the world, both warm and cold. A large amount of silica is found in the cuticle of the Horse-tails, associated also with fluorine. The rhizomes contain starch.

Nat. Ord. 271.—Musci, the Moss order (Fig. 361).—Erect or creeping, terrestrial or aquatic plants, with cellular stems, bearing minute cellular leaves. The organs of fructification consist of cylindrical, pear-shaped, or ellipsoidal stalked sacs, containing antheridial cells with phytozoa (Fig. 348), and of spherical or obovate archegonia, from which, after impregnation, are developed urn-shaped sporangia (Fig. 393), supported on stalks called setæ, and containing germinating spores. The sporangia have a calyptra, an operculum, and frequently a peristome, consisting of processes called teeth (Fig. 20), which are either 4 or some multiple of that num-

¹ For full details in regard to structure and reproduction in the different Cryptogamic natural orders, see pages 142 and 165. Botany. They are found in all parts of the world, and abound in moist temperate regions. Species between 1100 and 1200. There are two divisions of the order. Sub-order 1. Andraceae; Split-mosses; Sporangia calyptrate, splitting longitudinally into 4 equal valves, which are kept together at the summit by a persistent operculum. Sub-order 2. Bryaceae, true Urn-mosses; Sporangia calyptrate, opening at the summit, not by valves.

Nat. Ord. 272.—HEPATICAE, the Liverwort order (Fig. 362).—Plants having a cellular axis of growth which bears leaves on a thallus (Fig. 362). Antheridia (Fig. 363, a) and archegonia (Fig. 349) are placed either in the substance of the thallus, or on sessile or stalked processes. The stalks support sporangia or peltate sporangiferous receptacles. Sporangia sometimes open by valves, and bear elaters. The plants are generally distributed both in cold and warm climates, and more especially inhabit damp places. Some of the species of Marchantia, especially M. hemispherica, have been recommended as poultices in cases of Anasarca. The following are the divisions of the order:—Sub-order 1. Jungermanniaceae, the Scale-moss tribe; Sporangia opening by 4 valves, the spores mixed with elaters. Sub-order 2. Marchantiaceae, the true Liverwort tribe; Sporangia not opening by valves, bursting irregularly, spores mixed with elaters. Sub-order 3. Ricciaceae, the Crystalwort tribe; Sporangia not opening by valves, and having no elaters.

SUB-CLASS II.—THALLOGENAE, THALLOPHYTA, OR CELLULARES.

Nat. Ord. 273.—LICHENES, the Lichen order (Fig. 364).—Cellular plants, growing on stones, on the surface of the earth, or on trees, and taking up nourishment by all points of their surface, having a foliaceous, crustaceous, or leprous thallus (Fig. 364). Their fructification consists of thecae or asci, containing 4, 8, 12, or 16 spordia (Fig. 346). The thecae are often mixed with paraphyses, and by their union form circular, cup-shaped, or linear masses, which are called shields. There are also spermogones or conceptacles, containing cells with antherozoids, which are motionless, and have received the name of spermata. The spermogones are either in the substance of the thallus, or superficial, and the spermata are discharged through a pore. Between the upper and lower thalloid layers, green cells, called gonidia (Fig. 365), are found. Lichens are found in various parts of the world. The pulverulent species are the first plants which cover the bare rocks of newly-formed islands. Many of the Lichens are used for dyeing, others are employed as articles of food and medicine. Some Lichens are aromatic, and a fragrant powder called Cyprius at Rome is in part made from them. Oxalate of lime exists largely in some species, more especially in Variolaria. Cetraria islandica, Iceland-moss, contains starch, along with a bitter principle; it has been used as a tonic and demulcent. Cladonia rangiferina, is called Reindeer-moss, on account of supplying food for that useful animal. Leucania tortarea, called in commerce Rock-moss, supplies the dye denominated Cudbear. Roccella tinctoria is one of the Lichens imported under the name of Orchella-weed. The colouring matter is called Archil or Orchil; it is used for dyeing purple and red.

Nat. Ord. 274.—FUNGI, the Mushroom order (Fig. 367).—Cellular plants, with a spawn, mycelium (Fig. 18, m), by which they are nourished, and which bears organs of fructification of various kinds. Spores are produced, which are either naked (Figs. 18 and 368), or inclosed in these and mixed with elaters. There appear to be antheridial cells, containing spermatozoids, by the action of which on archegonial cells germinating spores are developed. In Agarics (Fig. 367) the mycelium bears tubercles inclosed in a volva, which ruptures so as to allow of the development of the stalked pileus, with its lamellae and hymenium. This order contains esculent and poisonous plants; the genus Agaricus, to which the true Mushroom belongs, contains both, and it is not easy to give rules for distinguishing the two kinds. Their qualities seem to depend in part on the mode in which they are prepared for food, and this may account for species which are eaten in some countries having proved poisonous in others. Fungi contain much nitrogen in their composition, and they do not appear to give out oxygen gas. They are often developed with great rapidity. The spawn spreads under ground, or in the interior of living or dead organisms, and when favourable circumstances occur, the fructification bursts forth with astonishing quickness. Many of them are developed on living plants, and cause disease and death by their parasitic growth. Agaricus campestris is the common Mushroom of Britain; it is distinguished in part by its pink gills. A. Georgii is another edible British species, which sometimes attains a large size. A. prunulus is said to be the most delicious Mushroom. Amanita muscaria* is a poisonous species, which produces giddiness and *plate narcotic symptoms. Morchella esculenta, Morel, is an edible Fungus. Penicillium glaucum is the common Mould fig. 1, developed wherever organic substances are in fitting conditions of moisture and temperature. The Vinegar-plant seems to be the abnormally developed mycelium of P. glaucum, or perhaps P. crustaceum. Sphaeria sinensis, is a Fungus parasitic on a caterpillar. It is a celebrated drug in China. Tuber is the genus which embraces the various kinds of Truffle (Fig. 366), an underground Fungus, which is scented out by dogs and pigs.

Nat. Ord. 275.—CHARACEAE, the Chara order (Fig. 21).—Aquatic plants composed of parallel cellular tubes, which give off whorled branches (Fig. 21), and which are often incrusted with carbonate of lime. In their tubes, rotation is observed. Their reproductive organs consist of globules containing antheridial cells with spirilla, and spiral mucilages containing germinating cells or spores (Fig. 373). Charas are found submerged in stagnant fresh or salt water in various parts of the world. They have a fetid odour.

Nat. Ord. 276.—ALGAE, the Seaweed order (Fig. 39).—Cellular plants, found in the sea, in rivers, lakes, marshes, and hot springs, all over the world, consisting of a brown, red, or green thallus, sometimes stalked, which bears the organs of fructification (Fig. 39). These consist of antheridial cells containing phytozoa, and of others containing germinating spores of different kinds (Figs. 370 and 371). These organs of reproduction are often united in the same conceptacle (Fig. 369 b). In other cases, they are on different parts of the same plant, or even on different plants. The spores sometimes have moving cilia, and are called zoospores (Fig. 8), at other times four are united so as to constitute tetraspores (Fig. 371). In some of the filamentous Algae there is a conjugation of 2 cells, so as to produce a spore (Fig. 19), in others there is a fissiparous division of cells (Fig. 13). Species of Algae abound both in salt and fresh water, whether running or stagnant, and in mineral springs. There are three colours in Algae, grass-green, olivaceous, and red. Some Seaweeds are microscopic, others growing in the depths of the Pacific have trunks exceeding in length those of the tallest forest trees, and fronds rivalling the leaves of the Palm. Many of the lower Algae approach nearly to some of the lowest animal forms, and it is difficult to form a line of demarcation. Species of Navicula, Pleurosigma, and other allied forms, are placed by some among Diatoms, by others among animals. Peculiar forms are met with in diseased states of the stomach and bladder, which are referred to Diatoms; one of them is called Sarcinula ventriculi. Achlya proliferis is sometimes produced on the gills of gold fishes, and other animals in a state of disease. The order has been divided in the following manner:—Sub-order 1. Melanospermum or Fucales, brown-coloured Seaweeds (Fig. 39); Marine plants of an olive-green or olive-brown colour, con- INDEX OF NATURAL ORDERS AND SUB-ORDERS.

| Order | Family | Order | Family | |-------|--------|-------|--------| | Ablettineae | 220 | Bruniaceae | 110 | | Acanthaceae | 166 | Brunoniaceae | 123 | | Acanthaceae | 47 | Bryaceae | 271 | | Accaraceae | 258 | Burmanniaceae | 232 | | Alangianaceae | 84 | Butomaceae | 254 | | Algae | 276 | Byttneriaceae | 32 | | Alismaceae | 252 | Cabombaceae | 9 | | Altinigaceae | 210 | Cactaceae | 104 | | Amaranthaceae | 172 | Cassalpinia | 75 | | Amaryllidaceae | 237 | Calitrichaceae | 197 | | Amentiferae | 209, 210, 211 | Calycanthaceae | 78 | | Ampelidaceae | 54 | Calycanthaceae | 121 | | Amygdalaceae | 71 | Cannabaceae | 126 | | Anardiaceae | 72 | Cannabaceae, see Urticaceae | 234 | | Andromedaceae | 271 | Cannabaceae | 234 | | Annonaceae | 4 | Caprifoliaceae | 16 | | Apiales | 112 | Caryophyllaceae | 28 | | Apocynaceae | 143 | Casuarinaceae | 213 | | Apotropaiae | 231 | Cedrelaceae | 52 | | Aquifoliaceae | 136 | Celastraceae | 68 | | Aquifoliaceae | 188 | Ceramiales | 275 | | Araceae | 257 | Ceramiales | 198 | | Araliaceae | 113 | Ceratophyllaceae | 70 | | Aristolochiaceae | 191 | Chailletiaceae | 87 | | Artocarpaceae | 200 | Chamlaucaceae | 87 | | Asclepiadaceae | 142 | Characeae | 273 | | Asteraceae | 122 | Chloranthaceae | 173 | | Atherospermaceae | 181 | Chloranthaceae | 205 | | Atropaceae | 160 | Chloranthaceae | 276 | | Aurantiaceae | 40 | Chrysobalanaceae | 77 | | Balanophoraceae | 219 | Clusiaceae | 122 | | Balsaminaceae | 210 | Cinchonaceae | 117 | | Balsaminaceae | 57 | Cistaceae | 19 | | Barringtoniaceae | 89 | Clusiaceae | 42 | | Basellaceae | 174 | Colchicaceae | 243 | | Begoniaceae | 179 | Columelliaceae | 129 | | Belvideriaceae | 95 | Combretaceae | 82 | | Berberidaceae | 8 | Comelinaceae | 248 | | Betulaceae | 121 | Compositae | 125 | | Bigoniaceae | 141 | Coniferae | 276 | | Bixaceae | 18 | Coniferae | 220 | | Boraginaceae | 156 | Compositae | 74 | | Brasiliaceae | 15 | Compositae | 153 | | Brexiaceae | 61 | Cordiaceae | 155 | | Bromeliaceae | 241 | Cornaceae | 114 | | Corylaceae | 212 | Filicites | 267 | | Corymbiferaceae | 122 | Flacourtiaceae | 18 | | Crassulaceae | 101 | Frankeniaceae | 23 | | Crescentiaceae | 148 | Fucales | 276 | | Cruciferae | 15 | Fumariaceae | 14 | | Cyperaceae | 93 | Fungi | 274 | | Cyperaceae | 109 | Galaxaceae | 118 | | Cyperaceae | 220 | Garriaceae | 216 | | Cyperaceae | 154 | Gaudichaudieae | 145 | | Cycadaceae | 223 | Geraniaceae | 54 | | Cycadaceae | 122 | Gennereae | 147 | | Cyperaceae | 235 | Gillespieae | 244 | | Cyperaceae | 39 | Globulariaceae | 155 | | Cyperaceae | 147 | Gnetaceae | 222 | | Cyperaceae | 218 | Goodeniaceae | 124 | | Cyperaceae | 265 | Gramineae | 105 | | Cyperaceae | 193 | Guttiferae | 42 | | Cyperaceae | 276 | Gyrostemonaceae | 176 | | Danaceae | 267 | Hamamelidaceae | 239 | | Danaceae | 193 | Haloragaceae | 91 | | Danaceae | 276 | Hamamelidaceae | 111 | | Danaceae | 224 | Hedeomaee | 113 | | Danaceae | 129 | Hepaticae | 272 | | Danaceae | 34 | Hippocastaneae | 48 | | Danaceae | 34 | Hippocastaneae | 44 | | Danaceae | 21 | Homalaceae | 97 | | Danaceae | 77 | Humiriaceae | 51 | | Danaceae | 77 | Hydrangeaceae | 108 | | Danaceae | 229 | Hydrocharitaceae | 229 | | Danaceae | 135 | Hydrophyllaceae | 151 | | Danaceae | 157 | Hypericaceae | 41 | | Danaceae | 238 | Hypoxidaceae | 238 | | Danaceae | 27 | Icacinaceae | 38 | | Danaceae | 194 | Illiciaceae | 136 | | Danaceae | 134 | Illecebraceae | 100 | | Danaceae | 270 | Iridaceae | 236 | | Danaceae | 311 | Iridaceae | 236 | | Danaceae | 263 | Jasminaceae | 132 | | Danaceae | 46 | Juglandaceae | 215 | | Danaceae | 106 | Junceae | 250 | | Danaceae | 195 | Junceae | 253 | | Danaceae | 75 | Jungmanniaceae | 272 | | Danaceae | 102 | Krameriacae | 23 | PART III.

GEOGRAPHICAL BOTANY, OR THE GEOGRAPHICAL DISTRIBUTION OF PLANTS.

This department of Botany is one of vast extent and importance, and the consideration of it would require much more space than can be allotted to it in the present article. All that we can attempt to do is to give some general facts regarding the distribution of plants over the globe, and to point out some of the causes which regulate this distribution.

The nature of the vegetation covering the earth varies according to climate and locality. Plants are fitted for different kinds of soil, as well as for different amounts of temperature, light, and moisture. From the Poles to the Equator there is a constant variation in the nature of the Flora. Between the Lichens and Mosses of the Arctic and Antarctic regions, and the Palms, Bananas, and the Orchids of the Tropics, there is a series of regulated changes in the number and forms of the members of the vegetable kingdom. The same thing is observed in the vegetation of lofty mountains at the Equator, in descending from their summit to their base. As we proceed from the Poles to the Equator, vegetation increases in amount and in variety. From a region characterized by the presence of Lichens, Mosses, Saxifrages, and Gentians, we come to that of Cruciferae and Umbelliferae; we then reach the grassy pastures, and the Coniferous and Amentiferous trees of temperate regions; and passing through the districts of the Vine, the Orange, and the dwarf Palm, to those of the Date, Coffee, Cotton, Sugar-cane, and Pine-apple, we arrive at the luxuriant vegetation of Equatorial regions. In this progress, as Humboldt remarks, we find organic life and vigour gradually augmenting with the increase of temperature. The number of species increases as we approach the Equator, and decreases as we retire from it. Each zone, however, has its own peculiar features. The Tropics have their variety and grandeur of vegetable forms, while the North has its meadows and green pastures, and the periodical awakening of nature in spring.

L—INFLUENCE OF CLIMATE, MORE ESPECIALLY OF TEMPERATURE AND MOISTURE, ON THE DISTRIBUTION OF PLANTS.

In determining the effects of climate on vegetation, our attention is chiefly directed to temperature and moisture,—to the daily, monthly, and annual distribution of heat, and to the amount of rain. We must also take into account light, the nature of the plant, its exposure, and many other causes, the effects of which are by no means easily estimated. They operate, however, usually within narrow limits, heat and moisture being the general agents. While in a given place the quantity of heat received varies according to different circumstances, it is found that the mean is pretty uniform. The quantity of heat is modified by winds and moisture. In China, for instance, the N.E. monsoon causes a great depression of temperature. The general preponderance of moist warm winds over dry cold ones is the reason why mild winters are more frequent in Europe than severe ones. Mountain chains, by intercepting winds, often produce a marked effect on climate. The effect of the sea in modifying the temperature is seen in insular climates, which are more equable than those of vast continents. Marine currents have also a decided influence on temperature. Thus the gulf-stream in the Northern Atlantic Ocean carries warm water towards the Arctic regions, and materially affects the temperature of the coasts around which it flows; while the Peruvian coast current, by bringing cold water from the antarctic regions towards the Equator, also modifies temperature. The temperature of the globe varies both as regards latitude and altitude, and vegetation at the same time undergoes changes. Latitudinally the globe, as regards temperature, may in a general way be divided into a tropical region extending from the Equator to 23° 28'; a sub-tropical, as far as 40°; a temperate from 40° to 60°; and a cold region beyond 60°. In a hypsometrical or altitudinal point of view, different zones of temperature are recognised, corresponding more or less with those of latitude. On an average, it may be said, that there is a difference of 1° of Fahrenheit for every 300 or 400 feet of ascent, and a difference of 1° of the thermometer in the boiling point of water for every 550 feet of ascent.

Each species of plants can bear a definite range of temperature. A certain amount of heat is also required during a given period of time, in order that a plant may be enabled to perform all its functions properly. Although a plant may continue to live in a certain climate, it may not thrive. The only true indication of climatal adaptation is, that the plant can perfect its seed and produce its various secretions. The latitude of a place does not at once tell the range of temperature. Many places in the same parallel of latitude differ widely in this respect. Lines, called Isothermal, have been drawn through places in which the mean annual temperature is the same, and it is found that while at the Equator these correspond nearly with the lines of latitude, as we recede from the Equator the two are widely separated. Yearly isotherms run in curves, rising in their course from the east of America towards the west of Europe, and sinking towards the south in the interior of the Continent. The yearly isotherm of 50° passes through latitude 42° 30' in the east of America, 51° 30' in England, 47° 30' in Hungary, and 40° in Eastern Asia. The want of conformity between the isothermal and latitudinal lines will be easily understood, when we consider that a place having a moderate summer and winter temperature may have the same annual mean as one having a very cold winter and a very warm summer. The vegetation in such districts would, however, be very different, and thus the annual isotherms are not sufficient for the purposes of botanical geography. Plants which stand the winter of London will not withstand the cold of places in Hungary in the same annual isotherm. In estimating, therefore, the effect of different climates on vegetation, attention must be paid also to the summer and winter heat. Lines passing through places with an equal mean summer heat are called Isotheral, while those indicating an equal mean winter temperature are called Isocheimal or Isocheimial. The latter in continents bend considerably towards the south, while the former bend towards the north, but approach nearer the parallels of latitude in the interior of continents. Some plants require a long period of winter repose and a few weeks only of warm and continued summer; others demand a dry season succeeded by a moist one. Some require a hot summer after an extremely cold winter of moderate duration; others succeed in a climate where the temperature of both seasons is moderate. In determining the limits of distribution in the vegetable kingdom, we must know the mean monthly and the mean daily temperature during those periods when vegetation is active. We must ascertain the number of days which a plant requires to produce successively its leaves, flowers, and fruit, and we must estimate the mean temperature during that period. The conditions which define the limits of a plant require that we should know at what degree of temperature its vegetation begins and ends, and further, the sum of the mean temperatures during that time.

Light and heat are so intimately connected, and so generally accompany each other, that the laws of the one are very nearly those of the other. Both of them are of the utmost importance in vegetation. Light is concerned in the various functions of plants. The physiological action of the leaves cannot go on without it, and the activity of vegetable life is in no small degree dependent on it. Some plants require full exposure to light, others luxuriate in the shade. The difference of the intensity of light in different countries influences the secretions of plants, and has a certain effect on the nature of the vegetation. While the chemical constitution of the atmosphere is nearly the same everywhere, its density varies much. This depends both on elevation and on the matters which may be suspended in it. It is probable that the varying density of the atmosphere at different elevations produces little or no effects in comparison with those which result from the modifications which the temperature, light, and humidity of the air undergo.

Moisture is an agent which exerts a powerful influence on the distribution of plants. Vegetation develops itself only when moisture is present. Very dry regions are deficient in vegetable productions, while the luxuriance of tropical vegetation is connected with great heat and moisture. Plants differ in regard to the quantity of moisture they require. Some are of a loose, spongy texture, with large, soft leaves, little or no pubescence, and many stomata, and demand a great deal of water. Others, growing in sandy, dry situations, where little rain falls, are firm and succulent, and often have long hairs and few stomata. The hard dry texture of the leaves of Banksias and other Australian plants, seems to be connected with the small amount of moisture in the atmosphere. Forests have a marked effect on the humidity of climates, and the felling of them has often been productive of very injurious consequences, by diminishing the quantity of water. In warm climates, the dry season may be said to correspond to our winter in its effects on vegetation. In some parts of South America, where no rain falls for many months of the year, the leaves during the dry season fall; buds are developed in their axils, and it is only when the wet season arrives that the trees become clothed with verdure, and the herbage appears.

Epiphytology or the influence of various physical agents on plants, is well illustrated by the variations in the epochs of foliation, defoliation, flowering, and fruiting. The unfolding of the leaves takes place at different periods of the year in different countries. Thus the Elm (Ulmus campestris) unfolds its leaves at Naples at the beginning of February, at Paris in the month of March, in England 14th April, and at Upsal about the middle of March. Schubler found in general that in the middle latitudes of Europe and North America, the flowering of plants is delayed four days for each degree of latitude towards the north. Berghaus remarks that in higher latitudes, in districts situated in the north of Germany, the development of vegetation is less re- tarded than in more southern positions. The delay in the period of flowering, between Hamburg and Christiania, amounts to only 3-4 days for one degree of approach towards the north, while that between southern Germany and Smyrna, in Asia Minor, which is in the same parallel as the most southern portions of Europe, amounts for the same space to 7-8 days.

Wheat harvest begins at Naples in June, in central Germany in July, in the south of England and the middle districts of Sweden about the 4th of August. Barley harvest commences at Naples in June, in central Germany about the end of July or beginning of August, in the south of England about the 14th of August, and in the middle districts of Sweden about the 4th of August. Ripe Cherries may be had at Naples during the first days of May, at Paris and in central Germany about the end of June, and in the south of England about the 22d of July. From observations made during two years in Saxony, we find, as a mean result, that from the flowering to the ripening of the fruit, 56 days are required for Wheat, 59 for Rye, 31 for Barley, 45 for Oats. Thurnmann states that in the Jura, generally speaking, a delay of 17 days in the harvest corresponds to a difference of altitude of 1000 feet. On the Alps, according to Schlagintweit, there is a delay of 11 days in the development of vegetation for every 1000 feet. Quetelet finds that in the climate of Europe every 600 or 700 feet produces a delay of about 4 days, which is equal to about 1° of latitude.

As regards the fall of the leaf, or defoliation, Berghaus remarks, that the Hazel-nut tree, the Ash, Lime, Poplar, and Maple, lose their leaves at Upsala at the very beginning of autumn; while in the neighbourhood of Naples they remain in full foliage during the whole month of November. The Apple-tree, the Fig-tree, the Elm, Birch, and different kinds of Oak, which in Paris are deprived of their leaves at the beginning of November, retain them at Naples till the end of December. In England, the Walnut is one of the first trees that loses its leaves; and after it the Mulberry, the Ash (especially when it has had much blossom), and then the Horse-chestnut.

II.—INFLUENCE OF SOILS ON THE DISTRIBUTION OF PLANTS.

Soils, or the media in which the roots of plants grow, regulate to a certain degree their distribution. In estimating this influence we must take into account the geognostic nature of the soil, its state of aggregation, its temperature, moisture, and exposure. Some plants are terrestrial, others are aquatic; some grow suspended in the air, others are parasitic. The effects produced by ordinary soils depend perhaps more on their mechanical nature than on their chemical composition. Hard, undecomposed felspar will bear a scanty vegetation, but when disintegrated and loose it affords abundant nourishment. The vegetation of limestone and trap rocks is more luxuriant than that of sandy soils. The moisture retained by aluminous soils is much greater than that by siliceous soils. Many plants seem to thrive best on chalky soils, others on siliceous, argillaceous, or peaty soils. Certain species grow only on soils impregnated with saline matters; others require to be within the influence of the sea. Parasites are often confined to peculiar species of plants.

Plants, in reference to the physical localities or stations in which they grow, have been divided into terrestrial, aquatic, marshy, epiphytic, and parasitic. Among terrestrial plants, the nature of the soil in which they grow gives rise to various groups. Arenaceous or sand plants have a peculiar character in all parts of the world, and the greatest number are probably grasses. Some of them bind the loose sand by their creeping stems. Calcareous or chalk plants are found on limestone rocks. Many Orchids belong to this division, especially species of Ophrys and Cypripedium.

Saline plants are those found in maritime situations, or near salt lakes, and which seem to require much soda in their composition, and which have been called Halophytes. Among them are species of Salsola, Salicornia, and Statice. Rupestral and mural plants are those found on rocks and walls, such as species of Saxifrage, Sedum, Draba, Sisymbrium, Parietaria, Linaria, Cymbalaria, Asplenium Ruta-muraria, A. Trichomanes, Lichens, and Mosses. Some also grow on the ruins of old buildings, and on rubbish-heaps, &c., near the habitations of man and animals. Among these are included Nettles, Docks, Hyoscyamus, Xanthium, and Sempervivum tectorum. Plants which grow in cultivated grounds, as in fields and gardens, may be said to form a special division. Among them may be noticed Centaurea Cyanus, Lychnis Githago, Spergula arvensis, Sinapis arvensis, Lollinia tenuilentum, Stellaria media, species of Lamium, Chenopodium and Euphorbia.

Plants of uncultivated ground are:—Meadow and Pasture plants, such as Grasses, Trefills, Clovers, species of Ranunculus, Veronica, Campanula, Galium, and Myosotis, Bellis perennis, Lotus corniculatus, Pimpinella Saxifraga, Gentiana campestris; Heath plants, such as Calluna vulgaris, the species of Erica, Juniperus communis, species of Ledum, Andromeda, and Polytrichum; Forest plants, growing in woods, such as the different kinds of trees; and the plants which grow under their shade, as Oxalis Acetosella, Trientalis europaea, Linnaea borealis, Geum rivale, Hepatica triloba, Vaccinium Myrtillus, and species of Orchis; Bush-plants, or those growing in bushy places, as Origanum vulgare, Corydalis bulbosa, Vincentoxicum officinale; Mountain plants, which vary much according to elevation, and which include species of Saxifraga, Gentiana, Primula, Rhododendron, Salix, Cyperaceae, Juncaceae, Labiatae, &c.; Hedge plants, such as Hawthorn and Sweet-briar, and the plants which twine among their branches, as Lonicera, Humulus, Bryonia, Tamus, Clematis, Lathyrus, as well the species of Viola and Adoxa, which grow at their roots.

Aquatic plants may either grow in salt or in fresh water. Among the former are marine species, such as the common species of Fucus, and other Seaweeds which grow buried in the ocean, and the Sargassum, or Gulf-weed, which floats on its surface; with them may be included such Planegamous plants as Zostera. Among the latter are some which root in the mud, and flower above the water, as species of Nymphara, Nuphar, Potamogeton, Ranunculus, Utricularia, and Sagittaria; others flower under water, as Subularia aquatica; while others float in the water, as species of Lemna, Pistia, Stratiotes, and various green fresh-water Algae. Some aquatics are fluviatile, as Ranunculus flavi-talis and (Enanthe fluviatilis; others grow in fresh clear water springs, or near them, as Montia fontana.

Marshy plants are those which grow in different kinds of wet soil. Some of them, as Comarum, Menyanthes, species of Bidens, (Enanthe, Cicuta, and Carex, grow in very wet places, which are not always easily accessible; others, as Primula farinosa, and Pinguicula alpina, grow in firmer, peaty soil. To this class may be referred certain amphibious plants, which generally grow submerged, but which can live in dry soil. Among them are included various forms of Ranunculus, Polygonum amphibium, Nasturtium amphibium, Limosella aquatica, as well as species of Rhizophora and Avicennia, which are found in warm countries at the muddy mouths of rivers.

Epiphytic plants are those which send their roots into the air, and grow attached to other plants. Among them are enumerated numerous species of tropical orchids (Fig. 70), and other air-plants, such as species of Tillandsia and Pothos.

Parasitic plants are those which derive nourishment from other plants. Among them are included those growing on living vegetables, such as species of Loranthus, Viscum (Plate Fig. 488), Lathraea, Orobanche, Cuscusa* (Fig. 426), Raf.-CXXV. flesia (Fig. 549), and many Fungi; those growing on dead vegetable or animal tissues, as the various Mould-plants (Figs. 422 to 425).

III.—DISTRIBUTION OF CLASSES, ORDERS, GENERA, AND SPECIES OF PLANTS OVER THE GLOBE.

Some plants are generally distributed over the globe, occurring in both hemispheres, and having an extensive latitudinal range; others are restricted and endemic in their distribution. There are numerous interesting facts in regard to geographical distribution in Hooker's Antarctic Flora, a work from which many of the following examples are taken. Trisetum subspicatum is a Grass having a very wide range. It extends from Tierra del Fuego over the whole of the Peruvian Cordilleras, and over the Rocky Mountains to Melville Island, Greenland, and Iceland; it is found in the Swiss and Tyrolean Alps, on the Altai, in Kamtschatka, and in Campbell's Island. The range is from 54° S. Lat., to 74½° N. Lat., through 128½ degrees of latitude. Drimys Winteri* extends over no less than 86 degrees of latitude, or 5160 geographical miles, forming at the southern limit of its growth one of the trees which advance nearest to the antarctic circle, and reaching as high a latitude as any flowering plant, save the solitary Grass of the South Shetland Islands. Gentiana prostrata has a great range, both in longitude and latitude. In southern Europe it inhabits the Carinthian Alps between 6000 and 9000 feet high; in Asia, it occurs on the Altai Mountains about N. Lat. 52°; in America, on the tops of the Rocky Mountains, in Lat. 52° N., at an elevation of 15,000 to 16,000 feet; and on the east side of the Andes of South America, in 35° S. It descends to the level of the sea at Cape Negro, in the Straits of Magallanais, in Lat. 53° S.; and at Cape Good Hope, in Behring's Straits, Lat. 68½° N. Potentilla anserina is widely distributed both in the northern and southern hemispheres. It grows throughout Europe, from the shores of the Mediterranean to the Arctic Sea; over all Asia to the north of the Altai range; in North America, from Lat. 40° to Whaleshank Island in 70° N. Lat.; and from the Oregon River to Kotzebue's Sound on the west coast. Epilobium tetragonum, a British plant, extends from Canada to Fuegia. Calitriche vernae is universally diffused through the temperate regions of both hemispheres. Many species in the Falkland Islands are identical with those found in Iceland. Galium Aparine is a British plant, found at the Cape of Good Hope, at the Straits of Magalhaens, in the island of Chloe; and in North America it ranges between the latitude of Fort Vancouver and the Mississippi River. Cryptogamic cellular plants have generally a very wide range; many of them are universally distributed.

Some plants which have a great latitudinal range are restricted to a narrow space as regards longitude. This is the case with the species of Erica, which extend from the Cape of Good Hope to northern regions. Certain species of Rhododendron, Magnolia, Azalea, Actaea, and Andromeda, occur on the east of the Rocky Mountains, and are not found on the western side. In the western part of Ireland we meet with Daboecia polifolia, Erica mediterranea, and Arbutus Unedo, which are not met with in other parts of Britain, and which again appear on the mountains of Asturias. On the western side of the Cordilleras of Chili, Calceolaria grow, which are not found on the eastern side. Lobelia Dortmannia seems to be confined to the western European countries.

While some plants are generally and widely distributed, others are limited to particular countries, and sometimes confined within very narrow limits. The floras of the different quarters of the world contain certain plants, which are restricted to them, and some which are only found in a few localities. One region in the Andes is marked by the occurrence of species of Bejaria, and another by Cinchonas. Certain plants belonging to the natural order Polemoniaceae are peculiar to California; an Orchid, called Disa grandiflora, is confined to Table Mountain; Codon Royenii and Protea acanthis are restricted to a few localities at the Cape of Good Hope. Numerous instances of a similar kind may be given, more particularly in the case of islands. The flora of islands near continents partakes of the character of that of the mainland. Those remote from continents, however, have often a more or less endemic flora. St Helena had a peculiar flora, which has been strangely altered by foreign introductions. Pringlea antiscorbutica, Kerguelen's Land Cabbage, is an interesting plant growing on an island, the remotest of any from a continent, and which, according to Hooker, yields, besides this esculent, only 17 other flowering plants.

We sometimes meet with marked centres, where the maxima of the genus of an order, or of the species of a genus, occur, the number of the genera or species diminishing as we recede from these centres, and ending perhaps in a solitary representative in some distant country. Gentians and Saxifragas have their maxima in the European Alps; Eriocaulons have their great centre in Brazil, but a few species are found in other countries. Epacridaceae are restricted to Australia. The genus Viola has two marked centres, one in Europe and another in America. The form of the European and American species are quite distinct. The maximum of the genus Erica is at the Cape of Good Hope; but members of the Heath family extend to northern regions in the form of Erica Tetralix, E. cinerea, and Calamagrostis vulgaris. The tropical Myrtaceae have Myrtus communis to represent them in Europe, Leptospermum in Australia, and Metrosideros lucida in Lord Auckland's group, Lat. 50½° S.

An order, or a genus, or a species, in one country is occasionally represented in another by forms which are either allied, or have a physiognomic resemblance. There is thus sometimes a repetition of resembling or almost similar forms in countries separated by seas or extensive tracts of land. The Ericaceae of the Cape have in Australia a representative in the nearly allied Epacridaceae; the Cactaceae of America are represented by certain succulent forms of Mesembryanthemaceae and Euphorbiaceae in Africa; and by some Crassulaceae in Europe. Trientalis europaea has a representative form in America, T. americana; Cornus suecica occurs in Europe, C. canadensis in Canada. Emeterium nigrum, in arctic regions, has E. rubrum to take its place in the antarctic; Pinguisula lusitanica, in the northern hemisphere, has P. antarctica closely resembling it in the southern; Hydnora africana and H. triceps in South Africa are represented in South America by H. americana.

The mode in which the globe has been clothed with vegetation, has given rise to much discussion. We know from the Sacred Record, that on the third day of the Creation the earth brought forth grass, and herb yielding seed after his kind, and the tree yielding fruit after his kind; but whether the whole earth was at once clothed with vegetation, or certain great centres were formed, whence plants were gradually to spread, we have no means of knowing. The endemic limitation of certain orders, genera, and species, would certainly lead to the opinion, that, in many instances, there have been definite centres, whence the plants have spread only to a certain extent. But the general distribution of other tribes of plants, and the occurrence of identical species in distant parts of the world, would favour the view, that countries with similar climates had originally many species of plants in common. In the case of Grasses, we would naturally suppose that they must have been produced in their social state, forming pasture for the nourishment of animals; and such we might conjecture to be the case with social plants in general.

Edward Forbes advocates strongly the view of specific centres, and endeavours to account for the isolation of certain species or assemblages of plants from their centres, by supposing that these outposts were formerly connected, and have been separated, by geological changes, accompanied with the elevation and depression of land. Schouw opposes this. He thinks that the existence of the same species in far distant countries is not to be accounted for on the supposition of a single centre for each species. The usual means of transport, and even the changes which have taken place by volcanic and other causes, are inadequate, he thinks, to explain why many species are common to the Alps and the Pyrenees on the one hand, and to the Scandinavian and Scotch mountains on the other, without being found on the intermediate plains and hills; why the flora of Iceland is nearly identical with that of the Scandinavian mountains; why Europe and North America, especially the northern parts, have various plants in common, which have not been communicated by human aids. Still greater objections to this mode of explanation, he thinks, are founded on the fact that there are plants at the Straits of Magalhaens, and in the Falkland and other antarctic islands, which belong to the flora of the arctic pole; and that several European plants appear in New Holland, Van Diemen's Land, and New Zealand, and which are not found in intermediate countries. Schouw, therefore, supposes that there were originally not one, but many primary individuals of a species.

Provision has been made for the extension of plants over the globe. The usual modes of transport are man, tides of the sea, rivers, winds, and birds. The Coco-nut wafted on the ocean is able to resist the action of the salt water by means of its fibrous covering; and lands on islands and shores in a state fit for germination. In this way recently produced coral islands are covered with vegetation. The hairy fruits and seeds of many plants are wafted to a distance by the winds, and rivers carry down the seeds of plants which have grown at their source. Birds which feed on pulpy fruits, often deposit the hard seeds at distant parts. Man, in his migrations, has distributed many plants, including common weeds, as well as plants useful for food or clothing.

Great changes have taken place in the distribution of many useful plants, chiefly by the agency of the Caucasian races, who have transplanted to their own countries the characteristic plants of other nations. Thus Schouw remarks—they have brought the Apricot, the Peach, and the Almond, from Asia Minor and Persia, and the Orange from China; they have transplanted Rice and Cotton to the Mediterranean coasts; they have brought the Maize and Potato from America to Europe. They have also carried their own characteristic plants to their colonies, and have transported into various climates useful and ornamental vegetable productions. European Corn plants have been widely spread through North America, in Mexico, the elevated countries of South America, Chili, Buenos Ayres, in South Africa, in the temperate parts of Australia and Van Diemen's Land. The Vine has been spread to Madeira, the Canary Islands, South Africa, and the high lands of South America. The Coffee-tree and Sugar-cane have been transplanted by man into the West Indies and Brazil; the Nutmeg and Clove into the Mauritius and Bourbon, and various West India islands; plantations of Tea have been formed in Brazil, Java, and India; Rice and Cotton have been cultivated in the warmer parts of North America and Brazil, and New Zealand Flax in New Holland.

The consideration of the distribution of the Cereal grains and of the Potato is a subject of much interest. The former have been so long cultivated, and so extensively spread, that it is difficult to discover their native country. They are not seen in a wild state, unless it be true, as Esprit Fabre says, that Æglops ovata is the wild condition of Wheat, and they have a wide geographical range, so as to be fitted for various climates. Rice is the grain which furnishes food to the greatest number of the human race; it is extensively used in warm countries, and more especially in China. Maize bears the greatest range of temperature, and succeeds in the hottest climates. Millet also is associated with it in hot countries. Wheat succeeds best on the limits of the subtropical region, and, as we proceed north, is succeeded by Rye, and then by Barley and Oats, which extend farthest north in Europe.

IV.—PHYSIOGNOMY OF VEGETATION IN DIFFERENT QUARTERS OF THE GLOBE.

In this department of botanical geography we consider plants according to the distribution of forms, marking the predominance of this or that form of plants by the absolute mass of its individuals or by the impression it makes from the character given to the flora. The prevalence of a single form will often produce a much greater physiognomic effect than the number and variety of the floral productions. Hinds says that a general physiognomic impression is sometimes conveyed by the prevalence of colour. Social plants in an especial manner, affect the landscape from growing in masses. There are certain marked vegetable forms which are concerned in determining the aspect or physiognomy of nature in different countries. Some of these leading forms coincide with natural orders; at other times, several distinct botanical groups require to be united.

The Palm Form (Fig. 82)—gives a marked character to the warmest regions of the globe, between 10 deg. north and 10 deg. south Lat. The true Palm climate has a mean annual temperature of 78-2 deg. to 81-5 deg. F. South America is conspicuous for the beauty and number of its Palms. With the Palm form has been associated the Cycadaceous order (Fig. 556),* which resembles it somewhat in the appearance of its naked stems and tufts of pinnated leaves.

The Banana and Plantain Form (Fig. 86)—is usually associated with the Palms in the torrid zone. In this form the physiognomist includes the natural orders Musaceae, Zingiberaceae, and Marantaceae. The plants representing this form have succulent herbaceous stems and long delicately-veined verdant leaves.

The Malvaceous Form—represented in warm climates by trees with thick trunks, large soft coriaceous or lobed leaves, and gorgeous flowers. It includes the Malvaceae, Buteaeaceae, Sterculiaceae, and Tiliaceae.

The Mimosa Form—is represented by Leguminosae, with delicately pinnate leaves (Fig. 132), and is met with both in warm and in temperate regions. It is not seen in the temperate zone of Europe, though found in the United States.

The Heath Form—belongs especially to the African continent and islands, as well as to Australia. Under it are included the species of Erica (Fig. 503) and Calluna, the Epacridaceae of Australia, the sub-order Diosmere of the order Rutaceae, and some Proteaceae.

The Cactus Form (Figs. 142 and 483)—with its peculiar jointed or spherical or polygonal stems without true leaves, is exclusively American. Some of the stems become hard and ligneous, and are very indestructible. Certain Euphorbias may be said to represent this form in Africa.

The Orchideous Form (Fig. 79)—is represented by the epiphytes which colonise the rocks and the trunks of trees in tropical climates, and which are distinguished by the animal shapes and colouring of their flowers.

The Casuarina Form—consists of leafless trees, with branches resembling those of Equisetum, found chiefly in the islands of the Pacific Ocean and in India. Along with phyllodiferous Acacias and some Myrtaceae, Casuarinas give a uniform character to the Tasmanian flora.

The Coniferous Form—is represented by the needle-leaved trees of northern regions, the Pines, Cypress, and Thuja; and by the broader-leaved Dammara and Salis- buria of more southern regions. In the Himalaya and Mexican mountains Coniferous and Palm forms are associated.

The Pothis Form—prevails chiefly in the tropics, and is represented by Pothos, Dracontium, Caladium, and Arum.* They have succulent stalks, large thick-veined leaves, and flowers more or less spathaceous.

The Liane Form—is represented by the twining rope-plants, the Pauliniias, Banisterias, Bauhinias, Bignoniias, Passifloras, and Aristolochias, of the hottest parts of South America, and the Hop and Vine of temperate climes.

The Aloe Form—consists of plants with succulent tufted leaves, found in arid regions, often growing singly, and imparting, according to Humboldt, a peculiar melancholy character to the tropical regions in which they are found.

The Gramineous or Grass Form—illustrated in tropical regions by arborescent Bamboos, and in temperate regions by meadows and pastures. Along with true Grasses are associated Cyperaceae, Juncaceae, Restionaceae, and Eriocaulonaceae. The genus Carex, is one of the Grassy forms of cold regions.

The Fern Form—gives a character to the landscape of warm and tropical regions. Like Grasses, Ferns have a gigantic appearance in the hotter parts of the globe. On the Andes they are associated with the Cinchona trees. In temperate insular climates, such as that of New Zealand, Ferns predominate.

The Liliaceous Form—includes the orders Liliaceae, Amaryllidaceae, and Iridaceae. In Southern Africa the species of Amaryllis, Ixia, and Gladiolus, with their ensiform leaves and gorgeous blossoms, represent this form. In America the Liliaceous form is represented by Alstroemeriaceae and species of Pancratium, Hemeranthus, and Crinum, which, however, are less social than the European Iridaceae.

The Willow Form—is represented by the species of Salix which spread over the northern hemisphere from the equator to Lapland. They increase in northern countries.

The Myrtle Form—gives a peculiar character to the south of Europe, especially the Mediterranean islands; to New Holland, in species of Eucalyptus, Melaleuca, Metrosideros, and Leptospermum; and to the district of the Pampas in the Andes, where certain species of Escallonia, Symplocos, Myrica, and Myrtus, are found.

The Melastoma Form—is represented by the species of Melastoma and Rhexia, with their ribbed and beautifully veined leaves, which abound in tropical America, and some of which ascend to 10,000 and 11,000 feet on the Andes.

The Laurel Form—is represented in South America by species of Lauris and Persea, as well as by some of the Guttiferae.

The Form of Dicotyledonous Trees—is represented in northern climates by the Oak, Beech, Elm, Horse-chestnut, Poplar, Alder, and Birch; in warmer climates by the Olive, and in the hottest regions by the large-leaved Breadfruit trees and Cecropias.

The Moss Form—is characteristic of cold regions. Hooker mentions, that in New South Shetland there are specks of Mosses struggling for existence. In Cockburn Island five Mosses are found.

The Lichen Form—is associated with Mosses, and may be said to extend still farther. It forms the limit of terrestrial vegetation. On Deception Island Lichens only exist.

V.—THE STATISTICS OF VEGETATION OVER THE GLOBE.

This subject involves the consideration of the number of known vegetable species in the world, their numerical distribution, and the relative proportion of classes, orders, genera, and species in different countries. In the present imperfect state of our knowledge of the floras of different countries, it is impossible to tell the exact number of species of plants in the globe. Those known at the present day, described and undescribed, amount probably to nearly 120,000, and from this estimates have been made of the total vegetation, the numbers varying from 150,000 to 200,000. The following is the estimated number of known and described plants:

| Genera | Species | |--------|---------| | Acotyledonous plants | 1,400 | 15,000 | | Monocotyledonous plants | 1,450 | 14,000 | | Dicotyledonous plants | 6,800 | 67,000 |

The relative numerical proportion of these great classes of plants varies in different quarters of the world. It is estimated that Cryptogamic plants are to Phanerogamous plants as 1 to 7. In northern and alpine regions the proportion of the former increases. In equatorial regions, Monocotyledons are to Dicotyledons in the proportion of 1 to 5 or 6; in temperate regions as 1 to 4; and arctic regions as 1 to 3. In temperate and cool climates there is an increase of Monocotyledonous plants, particularly of Gramineous forms. Tropical islands in general possess proportionally more Monocotyledons than do the continents; the usual proportion in these islands is said to be 1 to 4. An equable temperature, and a rather humid climate, are favourable to Monocotyledons. They diminish both under the extreme cold of the arctic zone and the great heat of the tropics. They increase towards the southern temperate and antarctic zones. Hooker remarks, that in St Helena Monocotyledons are to Dicotyledons nearly as 1 to 5, in the Society Islands as 1 to 42, in the Sandwich Islands 1 to 4, in the Cape de Verd Islands 1 to 5, in the Canaries 1 to 6, in Madeira 1 to 54, in the Azores 1 to 41, in Great Britain 1 to 4, in Shetland 1 to 33, in the Faroe Islands 1 to 24. There is thus an increase in the proportion of Monocotyledons in passing from the Canaries, Lat. 28°, to Madeira, Lat. 32°, the Azores, Lat. 38°, Great Britain, Lat. 50° 57', Shetland, Lat. 60°, and Faroe, Lat. 62°. In the arctic regions, on the other hand, Hooker remarks, the proportion seems to be inverted. In central and southern Europe, the proportion of Monocotyledons to Dicotyledons, which is 1 to 4 in the plains, decreases with the elevation on dry mountain slopes, till, at the height of 8526 feet, it is 1 to 7. Moist mountain slopes favour Monocotyledons, the proportion on them being as 1 to 3. In South Australia, Monocotyledons are to Dicotyledons as 1 to 4, varying, however, according to latitude, the mean being between the vegetation of New South Wales and Van Diemen's Land. In Western Australia, the proportion is 2 to 9, while the Acotyledons are to Dicotyledons as 1 to 6.

In the low plains of the great continents within the tropics, Ferns are to Phanerogamous plants as 1 to 20; on the mountainous parts of the great continents, in the same latitudes, as 1 to 8 or 1 to 6; in Congo as 1 to 27; in New Holland as 1 to 26. In small islands, dispersed over a wide ocean, the proportion of Ferns increases; thus, while in Jamaica the proportion is 1 to 8, in Tahiti it is 1 to 4, and in St Helena and Ascension nearly 1 to 2. In the temperate zone, Humboldt gives the proportion of Ferns to Phanerogamous plants as 1 to 70. In colder regions the proportion increases, that is to say, Ferns decrease more slowly in number than Phanerogamous plants. The proportion is least in the middle temperate zone, and it increases both towards the equator and towards the poles; at the same time, it must be remarked, that Ferns reach their absolute maximum in the torrid zone, and their absolute minimum in the arctic zone.

Taking other natural orders, we find that Juncaceae, Cyperaceae, and Gramineae increase in proportion to all the Phanerogamous species as the latitude becomes higher; thus, in the torrid zone, the proportion is 1 to 11; in the temperate zone 1 to 8, and in the arctic zone 1 to 4. Cinchonaceae, Leguminosae, Euphorbiaceae, and Malvaceae, increase in their proportion to Phanerogams as we approach the equator. The natural orders Cruciferae, Umbelliferae, and Compositae, have their highest quotients in the temperate zone. Piperaceae are plants of the hottest regions; Papaveraceae are chiefly European; Chinchonaceae, within the tropics, form 1-29th of the flowering plants; Scrophulariaceae, in the middle of Europe, are to Phanerogams as 1 to 26, in North America as 1 to 36. Labiate have their maximum between 40° and 50° N. Lat. Boraginaceae are chiefly confined to the temperate regions, while Primulaceae and Gentianaceae abound in colder zones.

The proportion of species as well as of genera, belonging to the same natural order, varies in different countries. Of Ranunculaceae 1-5th of the species are European, 1-7th North American, 1-17th South American, and 1-25th Indian; of Papaveraceae nearly 2-8ds are European; of Cruciferae 205 species, according to De Candolle, are found in the frigid zone of the northern hemisphere, 30 in the tropics (chiefly on mountains), 548 in the northern temperate zone, and 86 in the southern temperate zone. De Candolle states that about 1600 species of Leguminose are found in the equinoctial zone, about 1300 to the north of the tropics, and about 500 to the south. Of 9030 Compositae mentioned by authors, 3590 are found in America, 2224 in Africa, 1827 in Asia, 1042 in Europe, and 347 in the South Sea Islands. Of 2500 species of Euphorbiaceae 3-8ths are found in equinoctial America, 1-8th in tropical Africa, 1-6th in India, 50 species in America, and 120 in Europe. Lomler calculates that 165 Coniferae exist in the northern and 51 in the southern hemispheres. There are, according to him, 22 in Europe, 87 in Asia, 16 in Africa, 83 in America, and 35 in Australia.

VI.—ZONES OF VEGETATION AS REGARDS LATITUDE.

We have already seen that the vegetation varies according to latitude, and that we may trace a series of changes in the flora from the equator to the poles. Meyen proposes to mark out round the world a number of climacteric zones or belts, and to connect with the fact of these zones of climate the peculiarities of the vegetation of the belts. Meyen's plan is not quite correct, because he has made his belts to correspond with the parallels of latitude, and has asserted that between such and such parallels a certain form of vegetation would be found all over the world. The boundary lines of the zones, in order to be accurate, should be undulatory; they should correspond with the isotherm of the particular month in which there is the greatest development of vegetable life. Such undulatory zones, in which the plants present a certain resemblance to each other by sea and land, are denominated by Forbes Homoiozoic.

As regards vegetation, Meyen divides the Torrid zone into—1. The equatorial, extending 15° on both sides of the equator, having a mean annual temperature of 78°-8 to 82°-4 F. 2. The tropical, reaching from the 15th degree on each side of the equator to Lat. 23°, having a mean annual temperature of 73°-4 to 78°-8, a summer heat of 80°-6 to 86°, and a winter temperature in the eastern coast countries of 59°. The Temperate zone is divided by Meyen into—1. The sub-tropical, from the tropics to 34° Lat., with a mean annual temperature of 62°-6 to 71°-6, and a summer temperature of 73°-4 to 82°-4. 2. The warmer temperate zone, from Lat. 34° to 45°, having a mean annual temperature of 53°-6 to 62°-6, the summer temperature, in North America 77°, in Europe 68° to 75°-2, and in eastern Asia 82°-4; the winter temperature in America being 32°-54 to 44°-6, in Europe 34°-7 to 50°, and in eastern Asia 26°-6. 3. The colder temperate zone, between the parallels of 45° and 58°, the temperature of the year 42°-8 to 53°-6; the minimum summer temperature on the west coast 56°-31, in the interior of the continent 68°; the minimum winter temperature in the interior of Europe 14°. 4. The sub-arctic zone, from Lat. 58° to the polar circle in Lat. 66°-32, mean annual temperature 39°-2 to 42°-8; temperature of summer in America 66°-2, in the Old World 60°-8 to 68°; winter temperature of America 14°, of western Europe 24°-8, and of the interior of Russia 10°-4 to 14°. The Frigid zone is divided into—1. The arctic, from the polar circle to Lat 72°, mean annual temperature being 28°-4 to 32°, and towards the eastern continental regions much lower. 2. The polar, beyond 72° of latitude; mean annual temperature in the Old World 16°-7, in the New World 1°-4; the summer of the former 38°-3, of the latter 37°-4; winter of the former -2°-2, of the latter -28°.

Equatorial Zone.—This embraces central Africa, including the Guineo coast and Abyssinia, &c., Ceylon, the southernmost part of Hindustan, Malaya, Cochin-China, Sumatra, Borneo, Java, New Guinea, islands in the eastern seas, the northernmost part of Australia, the northern part of South America, including Columbia, Peru, the Guianas, and part of Brazil. The vegetable forms characteristic of this zone are Palmae, Musaceae, arborescent Grasses, Zingiberaceae, Marantaceae, Orchidaceae, and Lianas. Species of Bombax and Ficus occur here, with gigantic trees such as the Baobab, species of Swietenia, Hymenaea, and Casapinia. The orders Malpighiacese, Anonaceae, Anacardiaceae, Lecythidaceae, Sapindaceae, Artocarpaceae, Sterculiaceae, Ebenaceae, Meliaceae, Lauraceae, and Rafflesiaceae, are also well represented in this zone.

Tropical Zone.—This includes parts of Bolivia, Brazil, and Paraguay in South America, the majority of the West India Islands, Yucatan, Guatemala, and part of Mexico, Nubia and Senegambia in Africa, Madagascar, Mauritius, and North Australia, part of China and India, Burmah, and the south of Arabia. As Palms and Bananas may be said to characterize the equatorial zone, so may arborescent Ferns and species of Ficus be said to predominate in the tropical zone. Besides many equatorial forms, we meet here with plants belonging to the orders Piperaceae, Melastomaceae, and Convolvulaceae.

Sub-tropical Zone.—This embraces the north of Africa, including the Great Desert, Morocco, Barbary, Algiers, Tunis, Tripoli, and Egypt; in Asia, Palestine, Syria, north of Arabia, Persia, Cabul, Beloochistan, Thibet, the north of India, and China; the southern part of Australia; south Africa; Paraguay, La Plata, Chili, and Banda, in South America; the Bahamas, Bermuda, Mexico, Texas, the Southern States, and California, in North America. In this zone vegetation is green throughout all the year, like the forests of the damp regions of the torrid zone. It is called the region of Myrtaceae and Lauraceae. Certain Palm forms are seen, such as Phoenix dactylifera in Egypt (represented in India by Phoenix sylvestris and P. humilis), Hyphaene thebaica, Chamaerops Palmetto. In this zone we meet with succulent Crassulaceae, Mesebranthemaceae, Cactaceae, and arborescent Euphorbiaceae, plants belonging to the orders Tetrastomiaceae and Magnoliaceae; and in the southern hemisphere especially Proteaceae, Eucadidae, and Ericaceae, along with species of Zamia and Diosma.

Warmer Temperate Zone.—In Europe this includes the southern flora as far as the Pyrenees, the mountains in the south of France, and those in the north of Greece, Asia Minor, the country between the Black Sea and the Caspian, the north of China, and Japan lie in this zone. It has been called the region of evergreen trees. Chamaerops humilis represents the Palms, Erica arborea the Heaths, Laurus nobilis the Laurels, and Myrtus communis the Myrtles, in this zone, in which there are many sub-tropical forms. Spe- Colder Temperate Zone.—In the northern hemisphere the characteristic forms of the vegetation of this zone are seen in England, the north of France, and Germany. The forests consist of Dicotyledonous trees and especially Conifers; the successful cultivation of Wheat scarcely extends beyond the limits of this zone. Heaths, covered with Calluna vulgaris, add a feature in the physiognomy of this zone. The floras of Tierra del Fuego, the Straits of Magallanes, the Falkland Islands, and Kerguelen's Land, are also included in this zone. We meet with Drymis Winteri, Fagus antarctica, and F. Forsteri, Dactylis cespitosa, Pringlea antiscorbutica, and many other interesting forms described by Dr Hooker in his Flora Antarctica.

Sub-arctic Zone.—This zone is of less extent than the preceding, and in the interior of Asia it is perhaps not so easily distinguishable from it as it is in Europe. In the northern hemisphere it is the zone of Firs and Willows. In the southern hemisphere it embraces a few barren islands. The northern parts of Siberia and Norway, the Faroe Islands, and Iceland, belong to this zone. In the Faroe Islands Barley does not always ripen, but the Turnip and Potato succeed. The Amelanchier in them, as well as in Iceland, do not become trees. Grasses, Calluna vulgaris, and Juniperus communis, form features in the physiognomy of Iceland, and Alpine species come down nearly to the sea level. In Siberia, forests of Pinus Cembra, Larch, Spruce, Poplar, and Birch occur.

Arctic Zone.—In this zone the Birch predominates, and along with it are seen Pinus sylvestris and Abies excelsa. The Birch reaches nearly to North Cape, and Firs extend to 69° or 70°. Grasses are also found, and numerous Lichens and Mosses. At Hammerfest, in Lat. 71°, Potatoes, Turnips, Carrots, and Cabbage succeed. Species of Rhododendron, Andromeda, and Azalea occur in the American arctic zone.

Polar Zone.—In this zone there are no trees nor bushes, and no cultivation of plants for food. Species of Saxifrage, Dryas, Papaver, Ranunculus, Cardamine, Cochlearia, Pedicularis, Silene, Potentilla, Salix, Juncus, Eriophorum, Parrya, Platypetalum, Phrygia, Dupontia, and a few others, are found in this inhospitable belt. In Melville Island there are 67 species of flowering plants, in Spitzbergen 45. In cold zones we find more genera and fewer species than in warmer regions.

VII.—ZONES OF VEGETATION AS REGARDS ALTITUDE.

The vertical range of vegetation has been divided into zones similar to those of the horizontal range. The relation of plants to such zones of elevation is called Hypsometrical. As we ascend from the plain to the top of a mountain we pass through different belts of vegetation, the extent and variety of which differ in different countries. When Tournefort ascended Mount Ararat he was struck with the circumstance, that, as he left the low ground at the base of the mountain, he passed through a series of belts, which reminded him of the countries he had passed through in travelling from the south to the north of Europe. At the base the flora was that of the west of Asia; as he ascended higher he reached the flora of the countries on the north of the Mediterranean, then that of northern Europe, and when he reached the summit he found the Lapland plants. Humboldt found that on all mountains there occurs such a representation of different floras, and that particular alpine forms are found almost over the whole world at a particular elevation. In describing the South American alpine flora, he says—

"In the burning plains scarce raised above the level of the Southern Ocean, we find Musaceae, Cycadaceae, and Palmae, in the greatest luxuriance; after them, shaded by the lofty sides of the valleys in the Andes, arborescent Ferns; next in succession, bedewed by cool misty clouds, Cinchonas appear. When lofty trees cease, we come to Aralias, Thibaudias, and Myrtle-leaved Andromedas; these are succeeded by Bejarias abounding in resin, and forming a purple belt around the mountains." In the stormy region of the Paramos, the more lofty plants and showy flowering herbs disappear, and are succeeded by large meadows covered with Grasses on which the Llama feeds. We now reach the bare trachytic rocks, on which the lowest tribes of plants flourish. Parmelias, Leucideae, and Leprariae, with their many-coloured thalli and fructification, form the flora of this inhospitable zone. Patches of recently fallen snow now begin to cover the last efforts of vegetable life, and then the line of eternal snow begins."

Maiden and Strachey give the following account of the Himalayan vegetation, proceeding from the plains of India through Kenaon to Tibet:—"Ascending, we find forms of temperate climates gradually introduced above 3000 feet, as seen in species of Pinus, Rosa, Rubus, Quercus, Berberis, Primula, &c. At 5000 feet the arboreous vegetation of the plains is altogether superseded by such trees as Oaks, Rhododendron, Andromeda, Cypress, and Pine. The first ridge crossed ascends to a height of 8700 feet in a distance of not more than 10 or 12 miles from the termination of the plains. The European character of the vegetation is here thoroughly established, and although specific identities are comparatively rare, the representative forms are most abundant. From 7000 to 11,000 feet, the region of the alpine forest, the trees most common are Oak, Horse-chestnut, Elm, Maple, Pine, Yew, Hazel growing to a large tree, and many others. At about 11,500 feet the forest ends, Picea Webbiiana and Betula Bhojpura being usually the last trees. Shrubs continue in abundance for about 1000 feet more; and about 12,000 feet the vegetation becomes almost entirely herbaceous. On this southern face of the mountains the snow-line is probably at about an elevation of 15,500 feet. The highest dicotyledonous plant noticed was at about 17,500 feet, probably a species of Echinocereum. An Urtica also is common at these heights. The snow-line here recedes to 18,500 or 19,000 feet. In Tibet itself the vegetation is scanty in the extreme, consisting chiefly of Caragana, species of Artemisia, Astragalus, Potentilla, a few Gramineae, &c. The cultivation of Barley extends to 14,000 feet. Turnips and radishes on rare occasions are cultivated at nearly 16,000 feet. Vegetation ends at about 17,500 feet, scanty pasturage being found in favoured localities at this elevation; and the highest flowering plants are Corydalis, Cruciferae, Nepeta, Sedum, and a few others."

If we examine the vegetation of the mountains of Europe we shall find a series of similar changes. In the regions of the plains and lower hills of the Alps, extending to 1700 feet, the Vine grows; to this succeeds the zone of Chestnuts, which extends to 2500 feet; the zone of the Beech, and of the higher dicotyledonous trees, reaches from 2500 to 4000 feet; we then come to the sub-alpine region, the zone of Conifers, extending to about 6000 feet, in which are found the Scotch Fir, the Spruce, the Larch, and the Siberian Pine, along with certain sub-alpine forms of herbaceous plants; next comes the alpine region, or the zone of shrubs, extending to 7000 feet, characterized by Rhododendron Irsutum, and R. ferrugineum, which represent the Bejarias of the Andes; finally, we reach the subalpine region, extending to 8500 feet, and comprehending the part between the limits of shrubs and the snow-line, where we meet with numerous species of Ranunculus, Draba, Saxifraga, Gentiana, Primula, and Poa, besides other genera belonging to Ranunculaceae, Cruciferae, Caryophyllaceae, Leguminosae, Composite, Gramineae, Lichenes, and Musci. On some of the Alps we find flowering plants reaching to the height of between 10,000 and 11,000 feet or more. Schlagintweit found, on the central and southern Alps, at from 10,650 to 11,700 feet, Androsace glacialis, A. helvetica, Cerastium latifolium, Chelidonium sefoloides, Chrysanthemum alpinum, Gentiana bavarica, Ranunculus glacialis, Saxifraga bryoides, S. oppositiflora, and Silene acaulis. The extreme limit of Mosses in the Alps is in general little above that of Phanerogamous plants. The last Lichens are to be found on the highest summits of the Alps, attached to projecting rocks, without any limitation of height.

On the Pyrenees the following zones are observed— 1. The zone of Vine and Maize cultivation, and of the Chestnut woods. 2. A zone extending from the limit of the Vine to about 4200 feet, at which limit the cultivation of Rye ceases; here we meet with Buxus sempervirens, Saxifraga Geum, Eritmum alpinum, Arnica montana, &c., &c. 3. From the limit of the cultivation of esculent vegetables at 4200 feet, to the zone of the Spruce Fir. 4. From the limit of the Spruce Fir zone at 6000 to 7200 feet, characterized by the presence of the Scotch Fir. 5. From 7200 to 8400 feet, is an alpine zone, characterized by the dwarf Juniper, Draba aizoides, Saxifraga bryoides, Soldanella alpina, Juncus trifidus, &c. 6. A zone above 8400 feet, exhibits a few alpine species, as Ranunculus glacialis, Draba nivalis, Stellaria cerastoides, Androsace alpina, and Saxifraga grönlandica.

There are thus in lofty mountain districts evident belts of vegetation. At the lower part is the region of Lowland Cultivation, where the ordinary cultivated plants of the country thrive. In cold regions this is very limited, while in warm regions it is extended. To this region succeeds that of Trees. In high northern latitudes, as at 70°, it reaches to between 700 and 800 feet; on Etna to 6200; on the Andes to 10,800, and it is marked by Escallonia myrtilloides, Aralia aciculiflora, and Drymis Winteri; on the mountains of Mexico to 12,000 feet, and is marked by Pinus Monterezumae; on the south side of the Himalaya to 11,500, and on the north side to 14,000. On the Pyrenees its limits are marked at about 7000 feet by Pinus uncinata, on the Alps at about 6000 feet by Pinus Pinea, on the Caucasian mountains at 6700 feet; and in Lapland at about 1500 feet by the Birch. Next in order comes the Shrubby region, the limits of which in Europe are marked by Rhododendrons, which cease on the Alps of 7400 feet, and on the Pyrenees at 8332 feet; on the Andes it is limited by Bejarias and shrubby Compositae, at a height of 13,420 feet; on the south side of the Himalaya, by species of Juniper, Willow, and Ribes, at an elevation of 11,500 feet. In Lapland, species of Willow and Vaccinium, with the dwarf Birch, reach 3300 feet. The next region is that of Grasses, which on the Andes and the Himalaya extends to between 14,000 and 15,000 feet. Finally, we come to the region of Cryptogamic plants, which extend to the snow-line, Lichens being the last plants met with.

In contrasting the zones of altitude with those of latitude, Meyen gives the following regions of alpine vegetation—

The region of Palms and Bananas (equatorial) extending from the sea level to 1900 feet; the region of Tree-ferns and of Figs (tropical) 1900 to 3800 feet; the region of Myrtles and Laurels (sub-tropical) 3800 to 5700 feet; region of evergreen dicotyledonous trees (warm temperate) 5700 to 7600 feet; region of deciduous dicotyledonous trees (cold temperate) 7600 to 9500 feet; region of Abietine (sub-arctic) 9500 to 11,400 feet; region of Rhododendrons (arctic) 11,400 to 13,300 feet; region of alpine plants (polar) 13,300 to 15,200.

VIII.—SCHOUW'S PHYTO-GEOPHIC REGIONS.

In dividing the globe into Phyto-geographic regions, Schouw takes into account the nature of the flora in regard to species, genera, and orders, irrespective of the effects they may produce on the physiognomy of the country. In constituting a botanical region, he lays down the principle that at least one-half of the species and one-fourth of the genera should be peculiar to it, and that individual orders should either be peculiar to it or reach their maximum in it. He constitutes 25 Regions—1. Region of Saxifragas and Mosses. 2. Region of Umbelliferae and Cruciferae. 3. Region of Labiate and Caryophyllaceae. 4. Region of Asters and Solidagos. 5. Region of Magnolias. 6. Region of Camellias and Teas. 7. Region of Zingiberaceae. 8. Himalayan Alps. 9. Asiatic Islands. 10. Mountains of Java. 11. Islands of the Pacific. 12. Region of Balsam trees. 13. The Desert Region. 14. Region of Tropical Africa. 15. Region of Cactuses and Peppers. 16. Mountains of Mexico. 17. Region of the Medicinal Barks. 18. Region of Calceolarias and Escallonias. 19. West Indian Region. 20. Region of Palms and Melastomae. 21. Region of Tree Compositae. 22. Antarctic Region. 23. Region of Meseembryanthemums and Stapelias. 24. Region of Epericaceae and Eucalypti. 25. Region of New Zealand.

Region I.—The region of Saxifragaceae and Musci or the Alpine Arctic Flora.—This embraces the north polar lands from the limits of ice to the zone of trees, or what is called the Arctic Flora, in which Mosses, Lichens, and Cacti abound; and the upper parts of the mountains of Europe and northern Asia from the snow-line down to the arborescent belt, or the Alpine flora, in which Primulaceae and Saxifragaceae are prevalent. The mean temperature of the arctic division is 41° to 66°, that of the Alpine districts is 36° to 47°. In this region there is no cultivation.

Region II.—The region of Umbelliferae and Cruciferae.—This extends over northern Europe and Asia from the southern limit of the last region to the Pyrenees, the Alps the Balkan mountains, the Caucasus, and the Altai; the mean temperature being 36° to 57°. It is distinguished by the presence of Umbelliferous and Cruciferous plants. Coniferae, Amenitiferae, Ranunculaceae, Rosaceae, and Fungi are abundant.

Region III.—The region of Labiate and Caryophyllaceae or the Mediterranean Flora.—This comprises the countries of the Mediterranean Sea, Spain, the south of France, Italy, Greece, Asia Minor, Egypt, the whole of northern Africa to the Sahara and the great Atlas chain, the Canaries, and Madeira. The upper mountain regions belong to Schouw's first region, and the middle to his second. The mean temperature is 54° to 72°. The region is characterized by the prevalence of plants belonging to the Labiate and Cloverwort orders. Species of Compositae, Gallicaceae, and Boraginaceae also abound, and there is an increase in the plants belonging to the orders Leguminoseae, Malvaceae, Solanaceae, Urticaceae, and Euphorbiaceae.

Region IV.—The region of Asters and Solidagos.—This extends over the northern part of North America from the limits of the first region to the parallel of 30° north. Besides the number of species of Aster and Solidago (belonging to Composite), this region is marked by a great variety of Oaks and Firs, by numerous species of Vaccinium, by the smallness of the number of Cruciferae, Umbelliferae, Cinchonaceae, Cynarocephale, and by the absence of the genus Erica. The mean temperature is 64° to 72°. The Californian and Oregon districts, to the west of North America, constitute a region not yet fully explored. Many showy Polemoniacææ and interesting Coniferae are found here; also Eschscholtzia californica.

Region V.—The region of Magnolias.—This embraces the southern part of North America between the parallels of 30° and 36°. Here we meet with numerous tropical forms, as Zingiberaceae, Cycadaceae, Annonaceae, Sapindaceae, Melastomaceae, and Cactaceae. Mean temperature 59° to 72°.

Region VI.—The region of Ternstroemiaceae and Celastraceae, or the Japanese region.—This extends between the parallels of 30° and 40° N. Lat., and embraces Japan, the north of China, and Chinese Tartary, constituting the eastern temperate parts of the Old World. The flora seems to be intermediate between that of the Old and the New World. The vegetation is more tropical than European, for we meet with Zingiberaceae, Musaceae, Palmaceae, Cyca- ceae, Anonaceae. The mean temperature is $54^\circ$ to $68^\circ$.

**Region VII.**—The region of Zingiberaceae, or the Indian Flora.—This embraces India, the island of Ceylon, and the south-eastern peninsula, to the height of 4500 to 5500 feet above the level of the sea. There are here numerous specimens belonging to the Ginger order as well as to Leguminosae, Cucurbitaceae, and Tiliaceae. The Coco-nut, Mangosteen, Turmeric, Cinnamon, Cotton, Indigo, Clove, and Pepper, are abundant. Mean temperature $65^\circ$ to $75^\circ$. The south of China and Cochin-China may be considered as a distinct region. It partly resembles that of India, but contains many peculiar plants.

**Region VIII.**—The Emodic region.—This embraces the Alpine region of India south of the ridge of the Himalaya, including Sirmore, Gurwal, Kemon, Nepal, and Bhutan, to a height of from 4500 to 10,700 feet above the level of the sea. Some European species are met with in these high districts. Cedrus Deodara, Pinus excelsa, P. longifolia, Picca Webbiana, and other Conifers, along with Chamarops Khassiana, species of Oak, Dammar, Rhododendron, Berberis, Primula, &c., also occur. In the lower parts of the region tropical plants grow. The mean temperature is $37^\circ$ to $66^\circ$.

**Region IX.**—The region of the Asiatic Islands.—This comprises the mountainous districts of the islands between the south-eastern peninsula and Australia, to a height of 5500 feet above the level of the sea. Myristica moschata, Dryobalanops Camphora, and Dammara orientalis, grow in this region. Much of it is still unexplored. The mean temperature is $66^\circ$ to $84^\circ$.

**Region X.**—The region of Upper Java.—This comprehends the districts of the island of Java, and probably also of the numerous islands of the Asiatic archipelago, having an absolute elevation of 5500 feet above the level of the sea. Little is known in regard to the vegetation.

**Region XI.**—The Polynesian region.—This comprises all the islands of the Pacific Ocean within the tropics. Among the plants of this region may be mentioned Artocarpus incisa, Taccia pinnatifida, Cocos nucifera, Lodoicea seychellorum, Jambosa malaccensis, and many species of Arum, Dioscorea, Musa, and Ficus. The genera Dissochaeta, Orophea, Pterisanthes, Arthrophyllum, and Visenia, occur in this region. The mean temperature is $72^\circ$ to $82^\circ$.

**Region XII.**—The region of Amyridaceae.—This includes the south-western part of the highlands of Arabia. In the flora are many trees yielding gum and balsamic resins, such as species of Mimosa, Acacia, Balsamodendron, and Amyris. Coffee and the Sensitive-plant occur here.

**Region XIII.**—The Desert region.—This comprehends northern Africa, to the south of the Atlas Mountains, between Lat. $15^\circ$ and $30^\circ$ N., and the northern part of Arabia. Phoenix dactylifera and Hyphaene thebaica are characteristic plants of the region. The mean temperature is $72^\circ$ to $86^\circ$.

**Region XIV.**—The region of tropical Africa.—This comprises that part of Africa which lies between $15^\circ$ N. Lat. and the tropic of Capricorn, or, more correctly, between the northern and southern limits of periodical rains, with the exception of Abyssinia and the unknown countries of the interior. On the western part of this region, Elais guineensis the Palm-oil plant, and Adansonia digitata the Baobab, grow. On the coast of Guinea and Congo, the flora is intermediate between that of America and Asia, but chiefly resembling the latter. Species of Sorghum, Sterculia acuminata the Kola-nut, and the Poison-bean of Calabar, belong to this region. The mean temperature of the region is $72^\circ$ to $86^\circ$.

**Region XV.**—The region of Cactaceae and Piperaceae.—This embraces Mexico, Guatemala, the Isthmus of Panama, and South America as far as the river Amazon, and to an elevation of 5500 feet above the level of the sea, between Lat. $30^\circ$ N. and the equator. Guiana, New Grenada, and certain parts of Peru are included. Cactuses and Peppers abound in this region.

**Region XVI.**—The region of the Mexican Highlands.—This embraces the districts of Mexico which have an elevation of more than 5500 feet above the level of the sea. Some important Conifers are met with here, such as Pinus religiosa, P. apalensis, P. Hartwegii, P. Montezumii, and Taxodium distichum. The mean temperature is $64^\circ$ to $78^\circ$.

**Region XVII.**—The region of Cinchonas or medicinal Bark-trees. This comprehends the Cordilleras of South America, between the parallels of $5^\circ$ N. Lat. and $20^\circ$ S. Lat., at an elevation of 5000 to 9600 feet. The mean temperature is $59^\circ$ to $68^\circ$. In the lower part of the region Coffee and Maize are cultivated, and in the higher regions the European grains and fruits, along with the Potato and the Chenopodium Quinoa. Ceroxylon Andicola is also found in this region of the Andes.

**Region XVIII.**—The region of Escalloniae and Calceolariae.—This comprises the highest districts in South America above the upper limit of Cinchonas. The mean temperature varies from $59^\circ$ to $84^\circ$. Besides Escalloniae and Calceolariae, we meet with many alpine plants.

**Region XIX.**—The West Indian Region.—This region comprehends the West India Islands, the flora of which may be said to be intermediate between that of Mexico and the northern parts of South America. Ferns and Orchids prevail. Mean temperature $59^\circ$ to $78^\circ$.

**Region XX.**—Region of Palms and Melastomas.—This comprises that part of South America to the east of the Andes which lies between the equator and the tropic of Capricorn. Mean temperature $59^\circ$ to $82^\circ$. Here we have the luxuriant Brazilian flora. Palms, Melastomaceae, Myrtaceae, Tree-fruits, and Crotons, form the thick underwood, and beneath these, delicate herbaceous Ferns; Dorstenias, Heliconias, with a few tall Grasses, are found in the open parts.

**Region XXI.**—The region of arborescent Composites.—This embraces South America on both sides of the Andes from the tropic of Capricorn to Lat. $40^\circ$ S. In it are included the southern part of Brazil, La Plata, and Chili. Mean temperature $59^\circ$ to $75^\circ$. In Chili there are many genera which also are represented in Australia and at the Cape of Good Hope. Araucaria imbricata, the Banksian or Chili pine, is a hardy Conifer of this district, extending on the Chilián Andes from $37^\circ$ to $40^\circ$ S. Lat.

**Region XXII.**—The Antarctic region.—This embraces the southern part of America, the Straits of Magalhaens, Tierra del Fuego or Fuegia, the Falkland Islands, and others more to the south. Mean temperature $41^\circ$ to $46^\circ$. Many mountainous plants are found in this region. The vegetable forms of the north temperate and arctic zones prevail. Species of Saxifraga, Gentiana, Arbutus, and Primula, with many other European genera, abound. In Fuegia the Evergreen Beech, Fagus Forsteri, which never sheds its coriaceous foliage, is a very prevalent tree, also the Deciduous Beech, Fagus antarctica, the leaves of which change colour and fall, and Drymis Winteri. In the Falkland Islands there are about 120 flowering plants, consisting chiefly of those found on the mountains of Fuegia, and on the arid coast and plains of Patagonia.

**Region XXIII.**—The region of Mesembryanthemums and Stapelias.—This embraces southern Africa from the tropic of Capricorn to the Cape Coast. Mean temperature $55^\circ$ to $78^\circ$. Besides species of Mesembryanthemum and Stapelia there are a prodigious number of species of Erica. The latter genus attains its maximum here. We also meet with plants belonging to the orders Iridaceae, Bruniaceae, and Selaginaceae.

Region XXIV.—The region of Eucalypti and Eucalypti.—This comprehends Australia beyond the tropics with the island of Tasmania or Van Diemen's Land. Mean temperature 52° to 72°. The number of known Australian plants amounts to about 7000 or 8000. The flora of Australia approaches in its tropical portion to the plants of India, and in its extra-tropical portion to those of South Africa. The flora may be divided into a western, southern, eastern, and Tasmanian flora. In the western districts Leguminosae and Proteaceae predominate, forming one-fourth of the entire vegetation; Ferns and Grasses are rare. In the southern flora, Composite and Leguminosae abound along with Salsolas, Myoporaceae, Haloragaceae, Caryophyllaceae, and Cruciferae. The genus Meseembryanthemum is here seen as a connecting link with the South African flora; Nitraria with the Siberian, and Crantzia with the North American flora. In the eastern flora Proteaceae and Eucalypti are found, with fewer Compositae than in the south, and a larger number of Ferns and Grasses than in the western district. In South Australia, Compositae form 1-8th of the whole vegetation; Compositae and Leguminosae form together one-third of the whole of the Dicotyledons.

Region XXV.—The region of New Zealand.—This includes the islands of New Zealand and those which are adjacent. Between Lat. 34° and 36° S., the mean temperature is 61° to 63°. Here we meet with Phormium tenax the New Zealand Flax-plant, Corypha australis the southern Palm, abundance of Ferns, many of them arborescent species of Dracaena, many Myrtaceae, and some peculiar Coniferae. The known flora of New Zealand amounts to about 1900 or 2000 species, of which 730 are flowering plants, thus making Phanerogams to Cryptogams nearly as 2 to 3. Among the orders to which the endemic species belong may be noticed Coniferae, Scrophulariaceae, Euphorbiaceae, Compositae, Arales, Umbelliferae, Myrtaceae, and Ranunculaceae. The flora of the Auckland group and of Campbell's Island may be considered as a continuation of that of New Zealand, differing only in being more typical of the antarctic regions.

IX.—ZONES OF MARINE VEGETATION.

The ocean, as well as the land, possesses its vegetable forms, which are of a peculiar kind, and exist under different conditions of pressure, of surrounding medium, and of light. Some seaweeds, Harvey remarks, are cosmopolitan or pelagic, as species of Ulva and Enteromorpha, which are equally abundant in high northern and southern latitudes, as they are under the equator, and in temperate regions. Codium tomentosum, Ceramium rubrum, C. diaphanum, species of Ectocarpus, and several Corallinae, have a range nearly as wide. Flocamium coccineum and Gelidium corneum are common to the Atlantic and Pacific oceans; Rhodymenia palmata; the common Dulse of Britain, is found at the Falkland Islands and Tasmania. Fucus tuberculatus extends from Ireland to the Cape of Good Hope; Fucus vesiculosus occurs on the north-west coasts of America, and on the shores of Europe; while Desmarestia ligulata is found in the north Atlantic and Pacific oceans, as well as at the Cape of Good Hope and Cape Horn.

In general, however, Sea-weeds are more or less limited in their distribution, so that different marine floras exist in various parts of the ocean. The northern ocean, from the pole to the 40th degree, the sea of the Antilles, the eastern coasts of South America, those of New Holland, the Indian Archipelago, the Mediterranean, the Red Sea, the Chinese and Japanese Seas, all present so many large marine regions, each of which possesses a peculiar vegetation. The degree of exposure to light, and the greater or less motion of the waves, are very important in the distribution of Algae. The intervention of great depths of the ocean has a similar influence on sea-plants as high mountains have on land-plants. Laminariae are confined to the colder regions of the sea; Sargassa only vegetate where the mean temperature is considerable. Under the influence of the Gulf-stream, Sargassum is found along the east coast of America, as far as Lat. 44°; and the cold south polar current influences the marine vegetation of the coasts of Chili and Peru, where we meet with species of Lessonia, Macrocystis, D'Urvillea, and Iridaea, which are characteristic of the antarctic flora. Melanospermæ, according to Harvey, increase as we approach the tropics, where the maximum of the species, though, perhaps, not of individuals, is found; Rhodosperræme chiefly abound in the temperate zone; while Chlorospermæ form the majority of the vegetation of the polar seas, and are particularly abundant in the colder temperate zone. The green colour is characteristic of those Algae which grow either in fresh water or in the shallower parts of the sea; the olive-coloured Algae are most abundant between the tide-marks; while the red-coloured species occur chiefly in the deeper and darker parts of the sea.

As regards perpendicular direction, Forbes remarks, that one great marine zone lies between high and low water-marks, and varies in species according to the kind of coast, but exhibits similar phenomena throughout the northern hemisphere. A second zone begins at low water-mark, and extends to a depth of 7 to 15 fathoms. This is the region of the larger Laminarias and other Fuci. Marine vegetation, including the lower forms, extends to about 50 fathoms in the British seas, to 70, 80, or 100, in the Mediterranean and the Ægean Sea. Ordinary Algae, however, seem scarcely to exist below 50 fathoms. Diatomaceæ exist in the deep abysses of the ocean, and Nullipora and Corallines increase as other Algae diminish, until they characterize a zone of depth where they form the whole obvious vegetation.

The distribution varies also in a latitudinal or horizontal direction. Chorda Filum lies in beds of 15 to 20 miles in length, and only about 600 feet in breadth, in the North Sea and the British Channel. Sargassum bacciferum constitutes the Gulf-weed, which has been noticed by all who have crossed the Atlantic. The Sargasso Sea occupies the eddy or whirl caused by the revolution of the current in the Atlantic, and occupies a space of 260,000 square miles. The most remarkable of marine plants, both for their size and the extent of their range, are the Macrocystis pyrifera and the Laminaria radiata. Immense masses of the Macrocystis, like green meadows, are found in every latitude. It ranges from the antarctic to the arctic circle through 120 degrees of latitude. The tribe Fucoideæ abounds towards the poles, and there the plants attain their greatest bulk, diminishing rapidly towards the equator and ceasing some degrees from the Line itself. Cystoseæra represent the Fucoideæ in the higher latitudes of the southern hemisphere. Laminarias abound in the antarctic ocean and northwards to the Cape of Good Hope. The red, green, and purple Layers of the British seas are found at the Falkland Islands. Lessonia, with a stem 10 feet long and 12 inches in circumference, and its frond 2-3 feet long and about 3 inches broad, is found in immense masses off the Patagonian regions. D'Urvillea utilis is another large antarctic Seaweed, which, along with Lessonias, is often found at the Falkland Islands, formed by the surf into enormous vegetable cables, several hundred feet long, and thicker than the human body.

X.—DISTRIBUTION OF PLANTS IN BRITAIN.

The climate of Britain is warmer than that of other places in the same parallel of latitude. Its most striking feature is the absence of extremes, either as regards cold or heat. It is, generally speaking, mild and damp. While the winters are mild, the heat of the three summer months, June, July, and August, in which the growth and ripening of crops take place, is by no means great, being very little above that due to the latitude. The eastern coasts of Britain partake more of the continental climate, while on the western the climate is of an insular and equable character. The mean temperature varies from 46° to 52° F. Some of the mountains rise to the height of 4400 feet, and there is a fall of 1° of the thermometer of every 240 or 250 feet of ascent. The number of Phanerogamous species of plants amounts to about 1600, while the Cryptogamous are about 2800.

Taking a general view of the distribution of British Flowering Plants and Ferns (excluding the Hibernian and Sarmian species), Watson recognises the following types:

1. British type—species widely and generally spread over Britain, and forming probably 2-5ths of the British species, such as Alnus glutinosa, Betula alba, Corylus Avellana, Salix caprea, Rosa canina, Lonicera Periclymenum, Hedera Helix, Ranunculus sceleratus, Calluna vulgaris, Ranunculus acris, Cerastium triviale, Potentilla Tormentilla, Trifolium repens, Stellaria media, Lotus corniculatus, Bellis perennis, Senecio vulgaris, Carduus palustris, Leontodon Taraxacum, Myosotis arvensis, Prunella vulgaris, Plantago lanceolata, Polygonum aviculare, Urtica dioica, Potamogeton natans, Lemna minor, Juncus effusus, Carex prairea, Poa annua, Festuca ovina, Anthoxanthum odoratum, Pteris aquilina, Polypodium vulgare, Lastrea Filix-mas.

2. English type—species chiefly or exclusively found in England, and decreasing in frequency northwards, constituting about 1-5th of the whole flora, as Rhamnus catharticus, Ulex nanus, Tanus communis, Bryonia dioica, Hottonia palustris, Chiloa perfoliata, Sison Amomum, Moenchia erecta, Linaria Elatine, Ranunculus parviflorus, Lamium Galeobdolon, Hordeum pratense, Alopecurus aequalis, Ceterach officinarum, besides very local plants such as Cyperus longus and Cicindela filiformis.

3. Scottish type—species chiefly prevalent in Scotland or the north of England, forming about 1-20th of the flora, as Epipremnum nigrum, Rubus saxatilis, Trollius europaeus, Geranium sylvaticum, Trientalis europaea, Habenaria albida, Haloscias scoticum, Mertensia maritima; also Primula farinosa, Gooderia repens, Corallorhiza innata, and Saxifraga Hirculus, which are comparatively limited in their distribution and partial in their localities; besides some very local plants such as Arenaria norvegica, Primula scotica, and Ajuga pyramidalis.

4. Highland type—species either limited to the Scottish Highlands or extending to the mountains of the north of England and Wales; a more boreal flora than the last, the species being especially limited to the mountains or their immediate vicinity, and forming probably about 1-15th of the flora, as Azalea procumbens, Veronica alpina, Alopecurus alpinus, Phleum alpinum, Juncus trifidus, Silphidia procumbens, Erigeron alpinus, Gentiana rivasii; to these may be added the following, which, however, descend also lower, Salix herbacea, Silene acaulis, Saxifraga stellaris, Oxyria remiformis, Thalictrum alpinum, Luzula spicata, Juncus triglumis, Rubus Chamomorus, Epilobium alsinifolium, Draba incana, Dryas octopetala, Alchemilla alpina; likewise some very local species, as Lychnis alpina and Oxytropis campestris.

5. Germanic type—species chiefly seen in the east and south-east of England (bounded by the German ocean eastward)—forming about 1-15th or 1-20th of the flora, as Frankenia hirsuta, Anemone Pulsatilla, Reseda lutea, Silene noctiflora, Silene conica, Bupleurum tenuissimum, Pimpinella magna, Pulicaria vulgaris, Lactuca Scariola, Hallus pendulculatus, Aceras Anthropophora, Ophrys aranifera, Spartina stricta; also very local plants such as Veronica verna.

6. Atlantic type—species found in the west and south-west of England and Wales, having a tendency to the western or Atlantic parts of the island—forming about 1-15th or 1-20th of the flora, as Sinapis monensis, Matthiola sinuata, Raphanus maritimus, Sedum anglicum, Cotyledon Umbilicus, Euphrasia viscosa, Pinguicula lusitanica, Euphorbia Peplis and E. Portlandica, Scirpus Savii; also more limited species, as Sibthorpa europaea, Erica vagans, E. ciliaris, Physospermum cornubiense, Polycarpum tetraphyllum, Adiantum Capillus-Veneris, Cynodon Dactylon.

7. Local or doubtful type—species which cannot be referred to any of the preceding types, as Potentilla rupestris, Lloydia serotina, confined to peculiar mountains in Wales, Draba aizoides and Cotonaster vulgaris, found on the rocky coasts of Wales very locally, Draba muralis and Hutchinsia petraea; also Ericacolum septentrionale, found in the Isle of Skye, and formerly included under Watson's Hebridean type. If Ireland and the Channel Islands are also taken into account, Hibernian and Sarmian types would be added.

On ascending lofty mountains in Britain, there is a marked variation in the nature of the vegetation. On Ben-much-Dhu, which attains an elevation of upwards of 4000 feet, Watson gives a full list of the species observed in succession. On leaving the plants of the low country we find Myrica Gale, extending on this mountain to 1400 feet, and in succession we came to the upper limits of the following species—Erica cinerea, Pinus sylvestris, Carex pauciflora, Pedicularis sylvatica at 1838 feet, Tofieldia palustris, Erica Tetralix, at 2370 feet, Arctostaphylos Uva-Ursi, Thalictrum alpinum, Vaccinium Vitis-Idaea, Hieracium alpinum, Juniperus communis var. nana, at 2660 feet, Potentilla Tormentilla, Calluna vulgaris, 2690 feet, Azalea procumbens, Armeria maritima, Cochlearia groenlandica, Arabis petraea, Rubus Chamomorus, Epilobium alpinum, E. angustifolium, Vaccinium uliginosum, Silphidia procumbens, Saxifraga stellaris, Alchemilla alpina, Empetrum nigrum, Juncus trifidus, Gnaphalium supinum, and on the summit Silene acaulis, Carex rigida, Luzula arcuata and L. spicata, Salix herbacea.

Considering British plants in climatic or ascending zones, they are divided by Watson into—

I. Agrarian Region.—limited generally by the Pteris aquilina, and indicating the region of Corn cultivation. In the Highlands it may be said to extend as high at least as 1200 feet. It is subdivided into three zones—

1. Infer-agrarian Zone—embracing all the country southward from the Dee and Hamner, except the mountainous parts of Wales, and the higher hills and moors of the north of the Severn and Peninsulas (including Gloucester, Worcester, Warwick, Stafford, Hereford, Monmouth, Cornwall, Devon, and Somerset). Some of the peculiar species are Clematis Vitalba, Rabla peregrina, Cyperus longus, Erica ciliaris, Sibthorpa europaea, and Scilla autumnalis.

2. Med-agrarian Zone—all the low grounds, clear from the mountains, situate between the entrance of the Clyde and Tay on the north, and those of the Hamner and Dee on the south, also probably a narrow coast-line of the East Highlands, extending from Perth to Aberdeen, and possibly even to Inverness. Also a narrow belt extending round the hills of Wales, Rhamnus catharticus and Fragaria tanus communis, Bryonia dioica, Acer campestre, Ulmus glabra, Viburnum Lantana, Escoumia europaea, and Cornus sanguinea, occur in this zone, but are not restricted to it. There is no Clematis.

3. Super-agrarian Zone—coast-line and low plains and moors in the north and north-west of Scotland, where alpine plants descend to the sea-shore; such as Thalictrum alpinum, Draba incana, Saxifraga oppositifolia, Arctostaphylos alpina, and Dryas octopetala. Also other parts where the elevation of the ground leads to the production of the same species, or of such plants as Arctostaphylos Uva-Ursi, Saxifraga stellariis, Alchemilla pubescens, Thalictrum Juncus triglumis. Also traces of slight elevation in the proximity of high mountains, upon which a corresponding flora prevails. At its lower limits appear Hex, Caryus, Quercus, Fraxinus, Lonicera, Crataegus, and fruticose Rubi. II. Arctic Region—characterized by the absence of Corn cultivation.

1. Infer-arctic Zone—this has its terminal line at the limit of Erica Tetralix. 2. Mid-arctic Zone—space above the limit of Erica Tetralix, and within or below that of Calluna vulgaris. In this zone most of the rare alpine plants are found, such as Saxifraga nivalis, Gentiana nivalis, Erigeron alpinus, Astragalus alpinus, Veronica alpina, Alopecurus alpinus, &c. 3. Super-arctic Zone—above the limit of Calluna, characterized by Saxifraga cernua and rivularis, and Luzula arenaria.

Professor Edward Forbes has followed Watson in his views of distribution, and has promulgated a theory in regard to the origin of the flora of Britain. He considers the vegetation of Great Britain and Ireland as composed of several floras, which are to be reckoned outposts separated by geological changes from more extended areas. The following five floras, according to him, make up the vegetation of Britain and Ireland: 1. A west Pyrenean flora (Iberian or Asturian type), confined to the mountainous districts of the west and south-west of Ireland, characterized by botanical peculiarities, which depend on the presence of a few prolific species belonging to the families Saxifragaceae, Ericaceae, Lentibulariaceae, and Cruciferae. 2. A flora in the southwest of England and south-east of Ireland (Armorican type), which is intimately related to that of the Channel Isles and the neighbouring coast of France (Brittany and Normandy). This is Watson's Atlantic type. 3. The flora of the south east of England, where the rocks of the Cretaceous system are chiefly developed, and in which many species occur common to this district and the opposite coast of France. This corresponds nearly to Watson's Germanic type. 4. An alpine flora (Boreal or Scandinavian type), developed chiefly on the mountains of Scotland, and also partially on those of Cumberland and Wales. The species found on the latter are all, with the exception of Lloydia serotina, inhabitants also of the Scotch Highlands. The Scotch alpines all occur in Scandinavia, where they are associated with numerous additional species. This flora corresponds nearly to Watson's Highland type. This flora is represented in Shetland by Arenaria norvegica, and in Orkney by Primula scotica. It is largely developed on the Scottish Alps. 5. The general flora of the British islands, identical with that of central and western Europe, and which is called a Germanic flora. It corresponds to Watson's British, English, and Scottish types. It is a flora which overshadows many local floras throughout Europe, and gives a general character to the vegetation.

Forbes endeavours to prove that the specific identity, to any extent, of the plants of one area with those of another, depends on both areas forming, or having formed, part of the same specific centre, or on their having derived their vegetable population by transmission, through migration, over continuous or closely contiguous land, aided, in the case of alpine floras, by transportation on floating masses of ice. According to him, "the oldest of the floras now composing the vegetation of the British isles, is that of the mountains of the west of Ireland. Though an alpine flora, it is southernmost in character, and is quite distinct as a system from the floras of the Scottish and Welsh Alps. Its very southern character, its limitation, and its extreme isolation, are evidences of its antiquity, pointing to a period when a great mountain barrier extended across the Atlantic from Ireland to Spain. The distribution of the second flora, next in point of probable date, depended on the extension of a barrier, the traces of which still remain, from the west of France to the south-east of Britain, and thence to Ireland." The distribution of the third flora depended on the connexion of the coast of France and England towards the eastern part of the channel. Of the former existence of this union no geologist doubts. The distribution of the fourth, or alpine flora of Scotland and Wales, was effected during the glacial period, when the mountain summits of Britain were low islands, or members of chains of islands, extending to the area of Norway through a glacial sea, and clothed with an arctic vegetation, which in the gradual upheaval of those islands and consequent change of climate, became limited to the summits of the new-formed and still existing mountains. The distribution of the fifth or Germanic flora, depended on the upheaval of the bed of the glacial sea, and the consequent connection of Ireland with England, and of England with Germany, by great plains, the fragments of which still exist, and upon which lived the great elk, and other quadrupeds now extinct. The breaking up or submergence of the first barrier led to the destruction of the second; that of the second to that of the third; but the well-marked epoch of migration of the Germanic flora indicates the subsequent formation of the straits of Dover, and of the Irish Sea, as now existing."

While there are evident and distinct features in the plants which constitute the floras of different parts of Britain, there are many difficulties to be overcome before we can adopt the speculative views of Forbes. The connection between the Tertiary and the present epoch is not made out as far as the species of plants are concerned, and we are disposed to look upon the existing flora of the globe as a distinct and independent one. Schouw differs from Forbes in his explanation of the flora of the British islands. He does not believe in the migration and geological changes to which Forbes alludes. He thinks that the west and south-west coast of Britain and Ireland had at first a mild climate, especially in winter, and that in consequence plants were produced there common to the analogous climates of Spain and the south of France; while the Scotch and English mountains were distinguished throughout by a polar climate, and produced nearly the same vegetation as the Lapland and Scandinavian mountains.

D'Archiac says, that in a botanical point of view, it would, perhaps, be desirable to determine whether the external circumstances under which the five floras of Great Britain now live, such as latitude, altitude, temperature, winds, humidity or dryness, exposure, nature of the soil, greater or less distance from the coast, &c., are altogether insufficient to explain their different characters. We know that plants have very different geographical limits. Thus there are some which we meet with over an extent of 25° in latitude, and much more in longitude, while others occupy only zones extremely restricted in both senses; it would, therefore, be useful to study the five British floras in this point of view. The radiation of plants from a centre is by no means satisfactorily proved; and it may be asked, for example, what is the original centre from which the species common to North America and southern Europe could have radiated? D'Archiac thinks that inconvenience arises from an attempt to give an account of facts hitherto inexplicable in one science, by drawing from another science suppositions made, as it appears, with the sole view of these explanations, and for which there is no sufficient authority. Proofs drawn from geology must rest, on more certain data, he thinks, than those which have been adduced by Professor Forbes.

British marine vegetation presents two well-marked types according to Forbes, a southern and a northern. The genera Padina and Halysiris have their northern limit on the south coast of England, where they are rare. The genera Cystoseira, Sporochinus, Cutleria, and certain species of Sphacelaria, Mesogloea, Rhodymenia, Gigartina, and Dictyota, mark out a southern region, including the British Channel and part of the east coast, the Bristol Channel, and the south and west of Ireland; while the presence of Odonthalia denata, Rhodomela cristata, R. lycopodioides, and Fucus Macraei, characterize a northern flora, on the coasts of Scotland, the north of England and of Ireland. The proportion of the different marine plants on the shores of Britain are as follows:—Melanospermum 1-5th, Rhodospermum 3-8ths, and Chlorospermum 1-4th of the whole.

The British marine plants, according to Forbes, are distributed in depth or bathymetrically in a series of zones or regions which extend from high water mark down to the greatest explored depths. The first or littoral zone is that tract which lies between high and low water marks, and therefore is very variable in extent according to the amount of rise and fall of the tides. It has been divided into sub-regions characterized by the prevalence of certain marine species. 1. The sub-region of Fucus canaliculatus. 2. The sub-region of Lichina. 3. The sub-region of Fucus articulatus (Chlocladia articulata), F. nodosus, and Corallina officinalis. 4. The sub-region of Fucus serratus. The Littoral zone is succeeded by narrow belts of such Seaweeds as Himanthalia lorea, Conferva rupestris, Laurencia pinna-tifida, Chondrus crispus, and C. mammillosus. The second or Laminarian zone commences at low water-mark, and extends to a depth of from 7 to 15 fathoms. Here we meet with the great Tangle Seaweeds and deep-water Fuci. Species of Laminaria, Rhodymenia, and Delesseria, are found in an upper sub-region of this zone. In the lower sub-region they are rare, and are succeeded by the coral-like Nullipore. The zones below them are entitled the Coralline zone, extending from 15 to 50 fathoms, and the region of the deep-sea corals from 50 to beyond 100 fathoms. These zones do not exhibit any conspicuous vegetable forms; they are characterized by the presence of certain animals. At the depth of 50 fathoms in the British seas, there seems to be a total absence of vegetable life.

PART IV.

PALÆONTOLOGICAL BOTANY, OR THE STUDY OF FOSSIL PLANTS.

The changes which have taken place in the nature of living beings since their first appearance on the globe till the period when the surface of the earth having assumed its present form, has been covered by the creation which now occupies it, constitutes one of the most important departments in geology. It is, as Brongniart remarks, the history of life and its metamorphoses. The researches of geologists show clearly that the globe has undergone various alterations since that "beginning" when "God created the heavens and the earth." At various periods of the world's history, new mineral beds have covered the surface of the earth, and elevations of different portions of its crust have taken place, while at the same time the living beings inhabiting it have been buried in sedimentary deposits, to be replaced by a creation more or less different from the preceding. Some of these epochs have been marked apparently by great changes in the physical state of our planet, and they have been accompanied with equally great modifications in the nature of the living beings which inhabited it. The study of the fossil remains of animals is called Palaeozoology, while the consideration of those of vegetables is denominated Palaeophytology. Both are departments of the science of Palaeontology, which has been the means of bringing geology to its present state of advancement. The study of these extinct forms has afforded valuable indications as to the physical state of the earth and as to its climate at different epochs.

The vegetation of the globe, during the different stages of its formation, has undergone very evident changes. At the same time there seems to be no reason to doubt that the plants may all be referred to the great classes distinguished at the present day, namely, Thallogens, Acrogens, Gymnosperms, Endogens, and Exogens. The relative proportion of these classes, however, has been different, and the predominance of certain forms has given a character to the vegetation of different epochs. The farther we recede in geological history from the present day the greater is the difference between the fossil plants and those which now occupy the surface. At the time when the coal-beds were formed, the plants covering the earth belonged to genera and species not recognised at the present day. As we ascend higher, the similarity between the ancient and the modern flora increases, and in the latest stratified rocks we have in certain instances an apparent identity, at least as regards genera. At early epochs the flora appears to have been uniform, to have presented less diversity of forms than at present, and to have been similar in the different quarters of the globe. The vegetation also seems to indicate that the nature of the climate was different from that which characterizes the countries in which these early fossil plants are now found.

Fossil plants are by no means so easily examined as recent species. They are seldom found in a complete state. Fragments of stems, leaves, and fruits, are the data by which the plant is to be determined. It is very rare to find any traces of reproductive organs. The parts of fossil plants are usually separated from each other, and it is very difficult to ascertain what are the portions which should be associated together so as to complete a specimen. The anatomical structure of some of the organs, especially of the stem, can sometimes be detected by thin microscopic slices being placed under the microscope; and in the case of Coniferous wood, the punctated woody tissue has proved of great service as regards fossil Botany.

Brongniart says that the mode in which plants are preserved in a fossil state may be referred to two principal classes:—1. The impression or cast of the plants, accompanied with the complete destruction of the vegetable tissue, and the preservation of few of its constituent parts. 2. Petrifaction and Carbonization, which preserve more or less completely the structure of the tissues of vegetable organs, by changing them completely or only modifying them. The first state is rather rare, but it is the usual condition of fossil vegetables in the variegated sandstone and tertiary limestones. The place of the vegetable is either empty or replaced by a substance of a ferruginous, calcareous, or earthy nature, having no organization. The second state or the impression with some preserved portion of vegetable tissue, is very frequent in the case of stems found in the carboniferous system. This is their ordinary mode of preservation. In such stems we must carefully distinguish the different zones of tissue, and their external and internal surfaces, which produce so many different appearances. The silicified stems of trees have been observed in various parts of the world, with their structure well preserved, so that their Endogenous and Exogenous character can be easily determined.

In order to study fossil plants well, there must be an acquaintance with systematic botany, a knowledge of the microscopical structure of all the organs of plants, such as their roots, stems, barks, leaves, fronds, and fruit; of the markings which they exhibit on their different surfaces, and of the scars which some of them leave when they fall. It is only thus we can expect to determine accurately the living affinities of the fossil. Brongniart says, that before comparing a fossil vegetable with living plants, it is necessary to reconstruct as completely as possible the portion of the plant under examination, to determine the relations of these portions to the other organs of the same plant, and to complete the plant if practicable, by seeing whether, in the fossils of the same locality, there may not be some which belong to the same plant. The connection of the different parts of the same plant is one of the most important problems in Palaeophytology, and the neglect of it has perhaps led to a needless multiplication of fossil species; portions of the same plant having been described as separate species or genera. In some instances the data have been sufficient to enable botanists to refer a fossil plant to a genus of the present day, so that we have fossil species of the genera Ulmus, Alnus, Pinus, &c. Sometimes the plant is shown to be allied to a living genus, but differing in some essential point, or wanting something to complete the identity, and it is then marked by the addition of the term ites, as Pinites, Thaitea, Zamites, &c.

Before drawing conclusions as to the climate or physical condition of the globe at different geological epochs, the botanist must be well informed as to the vegetation of different countries, as to the soils and localities in which certain plants grow, whether on land or in the sea, or in lakes, in dry or marshy ground, in valleys or on mountains, or in estuaries, in hot, temperate, or cold regions. It is only by a careful consideration of all these particulars that any correct inferences can be drawn as to the condition of the globe.

The rocks of which the globe is composed are divided into two great classes, those which contain fossil remains, and which are called fossiliferous, and those having no such remains, and which are designated non-fossiliferous or azoic. The igneous unstratified rocks, included under the names of Granitic and Trappean, show no appearance of animal or vegetable remains. Trap rocks, however, have in some cases covered or inclosed vegetable structures, and these are found in an altered condition. Fossil remains have not been found in certain rocks having a stratified appearance, and which, from the changes they have undergone, were denominated by Hutton Metamorphic. These include Gneiss and Mica-slate, which are looked upon as stratified rocks, which have probably been formed at a high temperature, and have been subsequently altered by the effects of heat. The absence of organic remains in rocks, however, is not always sufficient to enable us to state that these rocks were formed before animals or vegetables existed. Forbes has shown that, even at the present day, there are depths in the ocean which are destitute of organic life. Hence rocks deposited at such depths might contain no organic remains.

The stratified rocks which contain fossils have been divided into three great groups, the Palaeozoic, the Secondary, and the Tertiary. The formations included under these are exhibited in the following table, as condensed from Ansted's geology:

1. **Palaeozoic Rocks**, containing the earliest fossil remains. They include the transition, Primary fossiliferous and Grauwacke rocks.

1. Lower Palaeozoic.—These comprehend the Silurian and Cambrian rocks. 2. Middle Palaeozoic.—The Devonian system, or Old Red Sandstone, so well developed in Scotland. 3. Upper Palaeozoic.—The Carboniferous system, or the Coal Measures, with millstone grit, carboniferous limestone, and shales; and the Permian system, or the magnesian limestone.

II. **Secondary or Mesozoic Rocks**, constituting a second great epoch in the history of fossils.

III. **Tertiary or Cainozoic Rocks**, constituting the third grand fossiliferous epoch. These are well developed in Asia, America, and in the south of Europe, and only partially in Britain.

1. Lower Tertiary or Eocene.—This is seen in the London clay, the Paris basin, the Basin of Brussels, &c. 2. Middle Tertiary or Miocene.—This is shown in the Coralline and Red Crag of Britain, the Basin of the Rhine, of the Loire, and Garonne, &c. 3. Upper Tertiary or Pliocene.—This is illustrated by the Norwich crag, the Till of the Clyde, the Brown coal of Germany, &c.

These are succeeded by Superficial or Pleistocene Deposits, which consist of diluvium or diluvial drift, formed of gravel, with boulders, which indicate the violent action of water; and alluvium or deposits of a second kind, resembling those caused by ordinary fluvial action. The tertiary formations and those of the present day appear to pass into each other.

The plants found in different strata are either terrestrial or aquatic, and the latter exhibit species allied to the salt and fresh-water vegetables of the present day. Their state of preservation depends much on their structure. Cellular plants have probably in a great measure been destroyed or changed in their aspect, and hence their rarity; while those having a woody and vascular structure have been preserved. The following is the number of fossil genera and species, as compiled from Unger's work on Palaeophytology:

| DICOTYLEDONES. | Genera. | Species. | |----------------|---------|---------| | Thalamiflorae | 24 | 84 | | Calyciflorae | 56 | 182 | | Cordiflorae | 23 | 60 | | Monochlamydæ | Angiospermae | 48 | 221 | | Gymnospermae | | 363 |

| MONOCOTYLEDONES. | Genera. | Species. | |------------------|---------|---------| | Dietynæ | 2 | 5 | | Petaloidæ | 36 | 125 | | Glumifloræ | 5 | 12 |

| ACOTYLEDONES. | Genera. | Species. | |---------------|---------|---------| | Thalloides | 31 | 203 | | Acrogynæ | 121 | 959 | | Doubtful | 35 | 197 |

| Total | 437 | 2421 |

These plants are arranged in the different strata as follows:

- Lower and Middle Palaeozoic (Cambrian, Silurian, Devonian, and Old Red Sandstone) 73 - Carboniferous 683 - Lower New Red Sandstone (Permian) 76 - Magnesian Limestone (Do.) 21 - Upper New Red Sandstone (Triassic) 38 - Shell Limestone (Do.) 7 - Variegated Marls (Do.) 70 - Atlas 126 - Upper, Middle, and Lower Oolite 168 - Wealden 61 - Upper and Lower Greensand 122 - Upper and Lower Chalk 122 - Eocene 414 - Miocene 496 - Pliocene 35 - Pleistocene 31

Fossil Species 2421 On taking a general survey of the known fossil plants, Brongniart thinks that he can trace three periods of vegetation, characterized by the predominance of certain marked forms of plants. In the most ancient period there is a predominance of Acrogenous Cryptogamic plants; this is succeeded by a period in which there is a preponderance of Gymnospermous Dicotyledons; while a third period is marked by the predominance of Angiospermous Dicotyledons. There is thus—1. The reign of Acrogens, which includes the plants of the Carboniferous and Permian periods. During these periods, there seems to be a predominance of Ferns, a great development of Lycopodiaceae, arborescent forms of Lepidodendron and Sigillaria, Gymnosperms allied to Araucaria, and anomalous Gymnosperms, as Noggerathia. 2. The reign of Gymnosperms, comprehending the lower and middle secondary periods. Here we meet with numerous Coniferae and Cycadaceae, while Ferns are less abundant. 3. The reign of Angiosperms, embracing the Cretaceous and the Tertiary periods. This is characterized by the appearance of Angiospermous Dicotyledons, a class of plants which constitute more than three-fourths of the present vegetable productions of the globe, and which appear to have acquired a predominance from the commencement of the Tertiary formations. These plants appear even at the beginning of the Chalk formation.

1. Reign of Acrogens.—In the lower Palaeozoic strata the plants which have been detected are few. In the Silurian, Cambrian, and Old Red Sandstone systems, we meet with the remains of ancient marine plants, as well as a few terrestrial species. In the Old Red Sandstone of Scotland, Miller has detected Fucoids, Ferns, a Lepidodendron, and Lignite with a distinct Coniferous structure resembling that of Araucaria, besides a remarkable pinnate frond. In the Old Red Sandstone rocks at Oporto, Bunbury detected Pecopteris Cyatha, P. muricata, and Neuropteris tenuifolia—ferns allied to those of the Coal Measures.

The Carboniferous period is one of the most important as regards fossil plants. The vegetable forms are numerous and uniform throughout the whole system, whether exhibited in the Old or the New World. The important substance called Coal owes its origin to the plants of this epoch. It has been formed under great pressure, and hence the appearance of the plants has been much altered. On examining thin sections of coal under the microscope, we can detect vegetable tissues both of a cellular and vascular nature. In Wigan cannel coal, vegetable structure is seen throughout the whole mass. Such is likewise the case with other cannel, parrot, and gas coals. In common household coal, also, evident traces of organic tissue have been observed. In some kinds of coal punctated woody fibre has been detected, in others dotted and scalariform tissue, as well as cells of different kinds. Sporangia are also occasionally found in the substance of coal, as shown by Mr Daw in that from Fordel. The structure of coal in different beds, and in different parts of the same bed, seems to vary according to the nature of the plants by which it has been formed. Hence the different varieties of coal which are worked. The occurrence of scalariform and dotted vessels in coal indicates the presence of Ferns, and their allied forms, such as Sigillaria, Stigmaria, and Lepidodendron; while true punctated wood (which is rarely seen except in brown coal) implies the presence of Coniferae. The anatomical structure of the stems of these plants will undoubtedly have some effect on the microscopic characters of the coal produced from them. The proportion of carbon varies in different kinds of coal. Along with it, there is always more or less of earthy matter, which constitutes the ashes. When the earthy substances are in such quantity that the coaly deposit will not burn as fuel, then we have what is called a shale. The coal contains plants similar to those of the shales and sandstones above and below it. In a coal-seam there is the Under-clay, containing roots only; then the Coal composed of plants, whose roots are in the clay, with others which have grown along with them, or have been drifted; while above the coal is the Shale bearing evidences of vigorous vegetation, and which appears like a great deposit from water charged with mineral matter, into which broken pieces of plants have fallen. There is frequently no clear division between coal and shale.

Unger enumerates 683 plants of the coal measures, while Brongniart notices 500. Of the last number there are 6 Thallogens, 346 Acrogens, 135 Gymnosperms, and 13 doubtful plants. This appears to be a very scanty vegetation, as far as regards the number of species. It is only equal to about 1/20th of the number of species now growing on the surface of the soil of Europe. Although, however, the number of species was small, yet it is probable that the individuals of a species were numerous. The proportion of Ferns was very large. There are between 200 and 300 enumerated.

Ferns are the only carboniferous fossil group which present an obvious and recognisable relationship to an order of the present day. While cellular plants and those with lax tissues often lose their characters by fossilization, Ferns are more durable, and retain their structure. It is rare, however, to find the stalk of the frond completely preserved down to its base. It is also rare to find fructification present. In this respect, fossil Ferns resemble Tree-ferns of the present day, the fronds of which rarely exhibit fructification. Only one surface of the Fern-frond is exposed to view, and that generally the least important in a botanical point of view. Fructification is sometimes evidently seen, as figured by Corda in Sentenbergia. The absence of fructification presents a great obstacle to the determination of fossil Ferns. The Acrogenous flora of the coal epoch seems to favour the idea of a humid as well mild and equable climate at the period of the coal formation—the vegetation being that of islands in the midst of a vast ocean.

Among the Ferns found in the clays, ironstones, and sandstones of the Carboniferous period, we may give the characters of some by way of illustration. Pecopteris seems to be the fossil representative, if not congener, of Pteris. Pecopteris heterophylla (Fig. 583) has a marked resemblance to Pteris escuelenta of New Zealand. The frond of Pecopteris is pinnatifid or bitri-pinnatifid—the leaflets adhering to the rachis by the whole length of their base, sometimes confluent; the midrib of the leaflets runs to the point, and the veins come off from it nearly perpendicularly, and the fructification when present is at the ends of the veins. Neuropteris (Figs. 584 to 586), has a pinnate or bipinnate frond, with pinna somewhat cordate. Botany.

at the base—the midrib of the pinnae vanishing towards the apex, and the veins coming off obliquely; and in an arched manner. Neuropteris gigantea (Fig. 585) has a thick bare rachis, according to Miller, and seems to resemble much Osmunda regalis. Sphenopteris (Fig. 587) has a twice or thrice-pinnatifid frond, the leaflets being narrowed at the base, often wedge-shaped, and the veins generally arranged as if they radiated from the base. Sphenopteris elegans resembled Pteris aquilina in having a stout leafless rachis, which divided at a height of seven or eight inches from its club-like base into two equal parts, each of which continued to undergo two or three successive bifurcations. A little below the first fork ing two divided pinnae were sent off. A very complete specimen, with the stipe, was collected in the coal-field near Edinburgh, by Hugh Miller, who has described it as above. Cyclopteris (Fig. 588) has simple orbicular leaves, undivided or lobed at the margin, the veins radiating from the base, with no midrib. Caulopteris is the name given to the stems of Tree-ferns found in the coal fields. They are marked externally by oblong scars similar to those of Tree-ferns of the present day. These stems probably belong to some of the fronds to which other names are given, but as they have not been found attached, it is impossible to determine the point.

Sigillaria is perhaps the most important plant in the coal formation. It is found in all coal shales over the world. There are upwards of 60 species. It occurs in the form of lofty stems, 40–50 feet high, and 5 feet broad (Figs. 589 and 590), standing erect at right angles to the planes of alternating strata of shale and sandstone. The stem of Sigillaria is fluted in a longitudinal manner, and has a succession of single and double scars, which indicate the points of insertion of the leaves. When the outer part of the stem separates like bark, it is found that the markings presented by the inner surface differ from those seen externally. This has sometimes given rise to the erroneous supposition that they belong to different genera. In Sigillaria elegans there is a woody system which is broken up into cuneiform plates, separated by medullary rays, and there are two vascular systems, one forming a series of bundles in the medullary axis of the stem, and another external to the woody system. The vessels are dotted, scalariform, and more or less referrible to the spiral type. The external bundles which go directly to the leaves are placed opposite to the woody wedges (not, as in Stigmaria, opposite to the medullary rays), and such is also the case with the inner vascular system.

It has been recently ascertained by Mr Binney of Manchester, that the plant called Stigmaria (Fig. 591) is not a separate genus, but the root, or rather the rhizome of Sigillaria. It is one of the most common productions of the coal measures, and consists of long rounded or compressed fragments, marked externally by shallow circular, oblong, or lanceolate cavities in the centre of slight tubercles, arranged irregularly, but sometimes in a quincuncial manner. The cavities occasionally present a radiating appearance. The axis of the fragments is often hollow, and different in texture from the parts around. This axis consists of a vascular cylinder or woody system, divided into wedge-shaped masses by medullary rays of which is considered as the root or rhizome of a Sigillaria. The markings are the points various breadths. In these rays there is another system of smaller tubes, which originate probably from the outer cellular axis, and not from the central woody cylinder. From the scars and tubercles arise long ribbon-shaped processes, which appear to have been hollow roots compressed. Stigmaria ficoides (Fig. 591), is often found creeping in the under-clay of a coal seam, sending out numerous roots from its tubercles, and pushing up its aerial stem, in the form of a fluted Sigillaria. While the rhizomes, stem, and roots have thus been determined, we have no means of ascertaining the foliage. It is probable that Sigillaria was an acrogenous plant allied to Lycopodiaceae, and probably intermediate between that order and Cycadaeae. In coal from Fordell, Mr Daw has detected numerous seed-like organisms, which may be the fructification either of a Sigillaria or of some plant allied to Lycopodium. The same bodies have been seen by Dr Fleming in many specimens of Cherry, Splint, and Cannel Coals from various quarters.

Lepidodendron (Fig. 592), is another genus of the coal measures which differs from those of the present day. It seems to occupy an intermediate place between Lycopodiaceae and Coniferae. The stem is from 20 to 45 feet high, marked outside by peculiar scaly-like scars (Fig. 592, a), hence the name of the plant. The linear or lanceolate leaves are arranged in the same way as those of Lycopodiums or of Coniferae, and the branches fork like the former.

There is a double vascular system in the trunk, one in the centre, and another placed externally to the woody mass. The latter vascular system forms a continuous zone outside the wood; its inner edge is well defined, and its outer, whence bundles are given off to the leaves, is sinuous. Although the scars on Lepidodendron are usually flattened, yet in some species they occupy the faces of diamond-shaped projections, elevated one-sixth of an inch or more above the surface of the stem, and separated from each other by deep furrows—the surface bearing the leaf being perforated by a tubular cavity, through which the bundle of vessels that diverged from the vascular axis of the stem to the leaf passed out. The fruit of Lepidodendron is seen in Lepidostrobus (Fig. 592, b and c), which appears to consist of scales covering sporangia, in the interior of which are spores, consisting of three or four angular sporules, which have been seen in a separate state. It is probable that many other fossil forms are connected with or allied to Lepidodendrons. Thus Lepidophyllum (Fig. 592, d) is probably the leaf of some species of the genus, while Strobilites is a form of the fruit.

Calamites (Fig. 593) is a reed-like fossil, having a sub-cylindrical, burrowed, and jointed stem, the furrows of the joints alternating and often converging. The stem is often crushed and flattened, and may probably have been originally hollow. At the joints there are toothed sheaths or tubercles, which are disposed symmetrically between the furrows. The fructification is unknown. There appears to have been a bark which could be separated from the woody tissue below. The plants have been seen erect by Mr Binney, and he has determined that what were called leaves or branches by some, are in reality roots. There are 51 species recorded. They have been compared to Equisetaceae.

True Exogenous trees exist in the carboniferous system both of England and Scotland. These Exogenous trees are Gymnosperms, having woody tissue like that of Coniferae. We see under the microscope punctated woody tissue, the rows of disks being usually two, three, or more, and alternating. They seem to be allied in these respects to Araucaria and Eutassa of the present flora. Stems of Dadoxylon or Pinites Withami, D. medullare, and Peuce Withami have been found in the sandstone of Craigleith quarry, near Edinburgh. Sternbergia is considered by Williamson as a Dadoxylon, with a discoid pith like that seen now-a-days in the Walnut and Jessamine.

The plants of the coal measures seem to be evidently terrestrial plants, and fresh-water aquatics. Brongniart agrees with Lyell in thinking that the layers of coal have in general accumulated in the situation where the plants forming them grew. The remains of these plants covered the soil in the same way as layers of peat, or the vegetable mould of great forests. In a few instances, however, the plants appear to have been transported from a distance, and drifted into basins. Phillips is disposed to think that this was the general mode of formation of coal basins. He is led to this conclusion by observing the fragmentary state of the stems and branches, the general absence of roots, and the scattered condition of all the separable organs. Those who support the drift theory, look on the coal plants as having been swept from the land on which they grew by watery currents at different times, and deposited in basins and large sea-estuaries, and sometimes in lakes. The snags in the Mississippi, the St Lawrence, and other large rivers, are given as instances of a similar drifting process.

The nature of the vegetation during the Permian Period, which is associated with the Carboniferous, under the reign of Acrogens, has not been positively determined. The genera of Ferns here met with are also found in the Carboniferous epoch; the Gymnosperms are chiefly species of Walchia and Noeggerathia. Lepidodendron elongatum, Calamites gigas, and Annularia floribunda, are also species of this period.

II. Reign of Gymnosperms.—In this reign the Acrogenous species are less numerous, the Gymnosperms almost equal them in number, and ordinarily surpass them in frequency. There are two periods of this reign, one in which Coniferae predominate, while Cycadaceae scarcely appear, and another in which the latter family preponderates as regards the number of species, and the frequency and variety of generic forms. Cycadaceae occupied a more important place in the ancient than in the present vegetable world. They extend more or less from the coal formation, up to the Tertiary. They are rare in the Grès-bigarré, or lower strata of the Triassic system (Upper New Red Sandstone) and in the Chalk. They attain their maximum in the Liass and Oolite, in each of which upwards of 40 species have been enumerated, and they disappear in the Tertiary formations.

In Brongniart's Vosgesian period, the Grès-bigarré, or the Red Sandstones and Conglomerates of the Triassic system, there is a change in the flora. Sigillarias and Lepidodendrons disappear, and in their place we meet with Gymnosperms, belonging to the genera Voltzia, Haidingeria, Zamites, Ctenis, Ethophyllum, and Schizoneura. Species of Neuropteris, Pecopteris, and other acrogenous coal genera are still found, along with species of Anomopteris and Crematopteris—peculiar Fern-forms, which are not found in later formations. In the saliferous red and variegated marls of the Triassic system, the Acrogens are changed as regards species, and frequently in the genera. Thus we have the genera Camptopteris, Sagenopteris, and Equisetum. Among Gymnosperms, the genera Pterophyllum and Taxodites occur.

In the Liass the essential characters of the flora are the predominance of Cycadaceae, in the form of species of Cycadites, Otozamites, Zamites, Ctenis, Pterophyllum, and Nilsonia, and the existence among the Ferns of many genera with reticulated venation, such as Camptopteris and Thaumatopteris. Coniferous genera, as Brachiphyllum, Taxodites, Palissya, and Pence, are found.

In the Oolitic epoch, the flora consists of numerous Cycadaceae and Coniferae, some of them having peculiar forms. Its distinctive characters are, the rarity of Ferns with reticulated venation, which are so numerous in the Liass, the frequency of the Cycadaceous genera Otozamites and Zamites, which are most analogous to those now existing; and the greater frequency of the Coniferous genera, Brachiphyllum and Thuites.

There is an absence of true coal fields in the secondary formations generally; but in some of the Oolitic series, as in the lower Oolite at Brora, in Sutherlandshire, and the Kimmerville clay of the upper Oolite, near Weymouth, there are considerable deposits of carbonaceous matter. The upper Oolite at Portland contains an interesting bed about a foot in thickness, of a dark brown substance, containing much earthy lignite. This is the dirt-bed, made up of black loam, which, at some far distant period, nourished the roots of trees, fragments of whose stems are now found fossilized around it. These consist of an assemblage of silicified stumps or stools of large trees, standing from 1-3 feet from the mould. Most of them are erect, some slightly inclined. Botany, and the roots remain attached to the earth in which they grew. They appear to resemble Cycadaceae. One of these is Cycadoidea megalophylla, shown in Figure 594.

The flora of the Wealden epoch is characterized in the north of England by the abundance of the Fern called Lomopteris Mantelli, and in Germany by the predominance of the Conifer denominated Abietites Linkii, as well as by numerous Cycadaceae, such as species of Cycadites, Zamites, Pterophyllum, Zamostrobos (Fig. 595), Cycadoidea, Clatharia. Mantell states that he has found 40 or 50 fossil cones in the Wealden of England. The remains are those of land vegetables. The Wealden fresh water formation terminates the reign of Gymnosperms.

III. Reign of Angiosperms.—This reign is characterized by the appearance of Angiospermous Dicotyledons, plants which constitute more than three-fourths of the present vegetable productions of the globe, and which appear to have acquired the predominance from the commencement of the Tertiary epoch. These plants, however, appear even at the beginning of the Cretaceous period. In this reign, therefore, Brongniart includes the upper secondary period, or the Cretaceous system, and all the Tertiary period. The Cretaceous may be considered as a sort of transition period between the reign of Gymnosperms and Angiosperms. The Chalk flora is characterized by the Gymnospermous almost equalling the Angiospermous Dicotyledons, and by the existence of a considerable number of Cycadaceae, which do not appear in the Tertiary period. The genus Cordyceps is one of the characteristic forms.

The Tertiary period is characterized by the abundance of Angiospermous Dicotyledons and of Monocotyledons, more especially of Palms. By this it is distinguished from the more ancient periods. Angiosperms at this period greatly exceed Gymnosperms. Cycadaceae are completely wanting in the European Tertiary strata, and the Coniferae belong to genera of the temperate regions. Although the vegetation throughout the whole of the Tertiary period presents pretty uniform characters, still there are notable differences in the generic and specific forms, and in the predominance of certain orders at different epochs.

The Eocene epoch in general is characterized by the predominance of Algae and marine Naiadaceae, such as Caulinites and Zosterites; by numerous Coniferae, the greater part resembling existing genera among the Cupressineae, and appearing in the form of Juniperites, Thuites, Cupresites, Callirhites, Frenelites, and Selenostrobos; by the existence of a number of Extra-European forms, especially of fruits, such as Nipadites, Leguminosites, Cucumites, and Hightes; and by the presence of some large species of Palm belonging to the genera Flabellaria and Palmacites. Amber is considered to be the produce of many Coniferae of this epoch, such as Picea succinifera.

The most striking characters of the Miocene epoch consist in the mixture of exotic forms of warm regions with those of temperate climates. Thus we meet with Palms, a kind of Bamboo, and other plants of warm climates, mingled with Amentiferous and other forms, belonging to temperate and cold climates.

The flora of the Pliocene epoch has a great analogy to that of the temperate regions of Europe, North America, and Japan. We meet with Coniferae, Amentiferous, Rosaceae, Leguminosae, Rhamnaceae, Aceraceae, Aquifoliaceae, Ericaceae, and many other orders. There is a small number of Dicotyledons with gamopetalous corollas. In this flora there is the predominance of Dicotyledons in number and variety; there are few Monocotyledons and no Palms. No species appear to be identical, at least with the plants which now grow in Europe.

Brown coal occurs in the upper Tertiary beds, and in it vegetable structure is easily seen under the microscope. Goeppert, on examining the brown coal deposits of northern Germany and the Rhine, finds that Coniferae predominate in a remarkable degree; among 300 specimens of bituminous wood collected in the Silesian brown coal deposits alone, only a very few other kinds of Dicotyledonous wood occur. The coniferous plants of these brown coal deposits belong to Taxinae and Cupressineae chiefly; among the plants are Pinites Protolarix and Taxites Ayckii.

We have thus seen that the vegetation of the globe has undergone various changes at different periods of its history, and that the farther back we go, the more are the plants different from those of the present day. There can be no doubt that there have been successive deposits of stratified rocks, and successive creations of living beings. We see that animals and plants have gone through their different phases of existence, and that their remains in all stages of growth and decay have been imbedded in rocks superimposed upon each other in regular succession. It is impossible to conceive that these were results of changes produced within the limits of a few days. Considering the depth of stratification, and the condition and nature of the living beings found in the strata at various depths, we must conclude (unless our senses are mocked by the phenomena presented to our view) that vast periods have elapsed since the Creator in the beginning created the heavens and the earth.

When we find animals and plants of forms unknown at the present day, in all conditions as regards development, we read a lesson in regard to the history of the earth's former state as conclusive as that which is derived from the Nineveh relics (independent of Revelation) in regard to the history of the human race. There is no want of harmony between Scripture and geology. The Word and the Works of God must be in union, and the more we truly study both, the more they will be found to be in accordance. Any apparent want of correspondence proceeds either from imperfect interpretation of Scripture or from incomplete knowledge of science. The changes in the globe have all preceded man's appearance on the scene. He is the characteristic of the present epoch, and he knows by Revelation that the world is to undergo a further transformation, when the elements shall melt with fervent heat, and when all the present state of things shall be dissolved ere the ushering in of a new earth, wherein righteousness is to dwell.

EXPLANATION OF THE PLATES.

Plate CX. Helleborus foetidus, Stinking Hellebore, belonging to the Nat. Ord. Ranunculaceae, Sub-ord. Hellebores. The leaves are pedate, the inflorescence cymose, and the fruit follicular.

Plate CXL Drimys Winteri, Winter's bark plant, belonging to the Nat. Ord. Magnoliaceae, and Sub-ord. Winteraceae. The plant was discovered by Captain Winter. Its bark is aromatic and stimulant, and its leaves are dotted.

Plate CXII. Papaver Rhoeas, common Red Poppy, belonging to the Nat. Ord. Papaveraceae. The leaves are pinnatifid, the peduncles have spreading hairs, the calyx consists of 2 caducous sepals, inslosing 4 crumpled petals, the stamens are indefinite and hypogynous, and the ovary is surmounted by a radiating stigma.

1. Stamens inserted on the thalamus, below the ovary with its sessile stigma.

2. Capsule of the Poppy opening by pores below the sessile stigma.

Plate CXIII. Janipha Manihot and Eschscholtzia californica.

Fig. 1. Janipha Manihot, Cassava plant, belonging to the Nat. Ord. Euphorbiaceae. The leaves are digitately-partite, and the flowers are in racemose cymes.

Fig. 2. Racemose cyme, with a pentacoccous capsule, which Botany.

separates in an elastic manner into 5 single-seeded carpels. The cyme bears male as well as female flowers.

Fig. 3. Pistil with stigma. Fig. 4. Stamens and fleshy disk. Fig. 5. Seed with strophiole. Fig. 6. Eschscholtzia californica (nat. size), belonging to the Nat. Ord. Papaveraceae. It has multipartite leaves, a peculiar caducous calyx like a camellia-exstipularizer, and a tetrapetalous corolla, which is a typical hypogynous stamen. Fig. 7. Hollowed end of the peduncle, with the pistil. The calyx separates in one piece from the peduncle. Fig. 8. Section of ovary, with numerous seeds attached to 2 parietal placentas. Fig. 9. Ceratium or Siliqueform capsule (nat. size), opening by 2 valves, and bearing seeds on each margin of the valves. Fig. 10. Section of the seed, with the Dicotyledonous embryo. Fig. 11. Embryo separated from the seed, showing the 2 cotyledons and the radicle.

Plate CXIV. Malva sylvestris, common Mallow, belonging to the Nat. Ord. Malvaceae. The leaves have 5 lobes, the inflorescence consists of cymose fascicles, the sepals are contorted, petals obcordate, and stamens numerous. Fig. 1. Calyx with 5 three-lobed sepals or involucre. Fig. 2. Single staminal petal, with monadelphous stamens. Fig. 3. Tube of stamens formed by union of the filaments. Fig. 4. Pistil with numerous carpels and styles. Fig. 5. Stamen with reniform anther opening round the margin. Fig. 6. Section of ovary composed of numerous carpels.

Plate C XV. Linum catharticum, and Linum usitatissimum, belonging to the Nat. Ord. Linaceae. Fig. 1. Linum catharticum, Purging Flax, having opposite oblong leaves, and a corymbose cyme. Fig. 2. Linum usitatissimum, Common Flax, having alternate lanceolate leaves and a corymbose cyme.

Plate CXVI. Amoranthus occidentalis, Cassow-nut plant, belonging to the Nat. Ord. Amaranthaceae. Fig. 1. Branch (somewhat reduced), bearing flowers and fruit. The flowers are in cymes, and the peduncles are enlarged in a pear-like form, bearing the nut (the true fruit) at their apex. Fig. 2. Flower not expanded, showing calyx and petals, with single fertile stamen and pistil. Fig. 3. Flower expanded. Fig. 4. Stamen and pistil, with the calyx. One fertile stamen longer than the others. Fig. 5. Stamen separated. Fig. 6. Nut constituting the fruit. Fig. 7. Nut opened longitudinally. Fig. 8. Seed separated from the nut. Fig. 9. Cotyledons opened to show the radicle a, and the plumule.

Plate CXVII. Sarothamnus scoparius (Spartium or Cytisus of many authors), Common Broom, belonging to the Nat. Ord. Leguminosae or Fabaceae, Sub-ord. Papilionaceae. The angled branches bear ternate leaves, papilionaceous flowers, and legumes. Fig. 1. Two-lipped calyx. Fig. 2. Broadly ovate Vexillum or standard. Fig. 3. One of the Ais, or wings, of the corolla. Fig. 4. Carina or Keel, which consists of 2 petals, and incloses the essential organs of reproduction. Fig. 5. Monadelphous stamens, i.e., united into a tube by their filaments. Fig. 6. Hairy ovary with the long style, thickened upwards, and spirally curved. Fig. 7. Legume or Pod, many-seeded and hairy at the margin.

Plate CXVIII. Carica Papaya, the Papaw tree (much reduced), belonging to the Nat. Ord. Papayaceae. The leaves are palmately-cleft, and the flowers are unisexual. Fig. 1. Portion of a racemose cyme of infundibuliform male flowers, with united petals. Fig. 3. Gamopetalous male flower cut open, showing the ten epicalcarine stamens alternately shorter. Fig. 4. Stamen consisting of filament and anther lobes. Fig. 5. Female flowers with a deeply-5-parted corolla and 5 stigmas above the ovary. Fig. 6. Andromeda hypomelaena (nat. size), belonging to the Nat. Ord. Ericaceae, creeping moss-like stem and pendulous, solitary, somewhat bell-shaped flowers. Fig. 7. Flower of Andromeda, with 5-parted calyx, gamopetalous, campanulate corolla. Fig. 8. Back view of stamen with its 2-horned anther. Fig. 9. Front view of stamen with bicorne and bipore anther.

Fig. 10. Pistil with its ovate acuminate style and 5-grooved ovary. Fig. 11. Capsule, 5-celled, with a central 5-lobed placenta bearing numerous ovules.

Plate CXIX. Petroselinum Cynapium, Fool's Parsley, belonging to the Nat. Ord. Umbelliferae. The leaves are bipinnate or tripinnate, with a sheathing pericarpodium, flowers in compound umbels, with a reflexed unilateral 3-leaved involucre connected with the umbellules. Plate CXX. Conium maculatum, Common Hemlock, belonging to the Nat. Ord. Umbelliferae. The stem is spotted and hollow, leaves compound (tripinnate), with a pericarpodium, flowers in compound umbels, with an involucre and an involucel, fruit a cremocarp with waved ridges. Plate CXXI. Chamaemeles crocea, Hemlock Water-Dropwort, belonging to the Nat. Ord. Umbelliferae. Leaves compound and sheathing, root composed of fibrous seminal tubers, stem hollow, and flowers in compound umbels with central and lateral involucres. Fig. 1. Flower composed of 5 petals, with inflexed apicals, 5 stamens, and 2 styles with an epigynous disk. Fig. 2. Lateral view of the cremocarp composed of 2 mericarps or achenes, with blunt convex ribs, surmounted by the lanceolate teeth of the calyx, and two styles with a disk at their base. Fig. 3. Back view of the cremocarp, with ribs, teeth of calyx, and styles.

Plate CXXII. Valeriana officinalis, Great Wild Valerian, belonging to the Nat. Ord. Valerianaceae, showing the roots, which are officinal, the hollow stem, the alternately-pinnate leaves, and flowers in corymbose cymes. Fig. 1. Solitary flower, consisting of an adherent calyx, with an irregular limb, an irregular gamopetalous corolla, exserted stamens, and 1 style. Fig. 2. Pistil separated, with ovary, style, and stigma. Fig. 3. Monoperal fruit, with the persistent pappose limb of the calyx.

Plate CXXIII. Lactuca virosa, Strong-scented Wild Lettuce, belonging to the Nat. Ord. Composite, Sub-ord. Cichorioceae. The leaves are sessile, amplexicaul at the base, and dentate. The flowers in capitula, and the calyx pappose.

Plate CXXIV. Leontodon Taraxicum, Common Dandelion, belonging to the Nat. Ord. Composite, Sub-ord. Cichorioceae. The leaves are radical and runcinate, the flowers ligulate, and arranged in capitula. The fruit (pericarp, or seed vessel) are reflexed, and all of them become deflexed when the fruit is ripe; the receptacle becomes dry and convex. Fig. 1. Capitulum with reflexed phyllaries and ligulate flowers. Fig. 2. A single flower, with inferior achene (cypsela), stipitate pappus, a ligulate corolla, 5 stamens united by their anthers, and 1 style with 2 stigmas. Fig. 3. Receptacle of the flowers, become dry and convex, with deflexed phyllaries, so as to allow the pappose fruit to be scattered. Fig. 4. Linear-obovate Achene, or Cypsela, consisting of an indehiscent single-seeded seed-vessel, which is muriated towards the apex, and longitudinally striated.

Plate CXXV. Cuscuta verrucosa, Warty Dodder, belonging to the Nat. Ord. Convolvulaceae, which is often considered as a sub-order of Convolvulales. Fig. 1. Leafless flowering stem of Dodder (nat. size) turning from right to left (contrary to the motion of the sun), bearing racemose cymes. Fig. 2. Campanulate corolla, cut open, showing 5 epicorolline stamens, with alternating scales at their base. Fig. 3. Persistent calyx, surrounding the pistil. Fig. 4. Capsule opening transversely near the base, exposing seeds and dissepiment. Fig. 5. Dissepiment and 2 seeds, the upper part of the capsule being removed. Fig. 6. Bilocular capsule cut transversely, showing 2 seeds in each locule. Fig. 7. Roundish compressed seed. Fig. 8. Seed cut longitudinally, showing the albumen with portions of the spirally-rolled-up embryo immersed in it.

Plate CXXVI. Solanum nigrum and Solanum Dulcamara, belonging to the Nat. Ord. Solanaceae. Fig. 1. Solanum nigrum, Common Nightshade. Leaves ovate and wavy. Flowers in extra-axillary umbellate cymes. Fig. 2. Solanum Dulcamara, Woody Nightshade or Bitter-sweet. Stem shrubby, leaves auricled, flowers in corymbose cymes opposite the leaves. Fig. 3. Anther opening by 2 pores at its apex. Fig. 4. Transverse section of baccate fruit, showing 2 loculicids, with seeds attached to a central placenta. BOTANY Bay, a spacious bay on the east coast of Australia, New South Wales, 5 miles south of Sydney, in Lat. 34° S. Long. 157° E. It was discovered by Captain Cook in 1770, and named from the profusion of then unknown plants found on its shores. The bay is about 5 miles in length and breadth, but the entrance is little more than a mile across. See AUSTRALIA.