Under the article BOTANY, and also under PLANT, we have already delivered some of the commonly received doctrines on this subject. But as some late investigations seem to lead to new views with regard to the structure and nature of vegetables, we have thought it necessary to resume the subject, and to give as full a detail of the experiments and observations to which we allude as our limits will permit; we shall first treat of the structure, and secondly of the physiology of plants.

I. STRUCTURE OF PLANTS.—In considering the structure or anatomy of plants, we shall treat, 1st, of the root; 2d, of the stem and branches; 3d, of the leaves; and 4th, of the flowers; in the order in which they are now enumerated.

1. The Root.—The root is that organ belonging to vegetables by which they are supplied with nourishment, and by which they are fixed to a commodious situation. It was formerly supposed to be composed of outer and inner bark, of wood, and of pith; but Mrs Ibbetson, who has lately communicated to the public the results of an elaborate vegetable elaborate series of experiments on this subject, thinks physiology, that it is wholly composed of the rind much thickened, with perhaps a very little of the outer bark, but no inner bark; of a quantity of wood, hardly any pith, and no spiral vessels. Mrs Ibbetson searched in vain for the larger vessels of the inner bark, till it occurred to her that the want of this bark accounted for there being no leaves on the root. Mrs Ibbetson had often been assured that roots were found bearing leaves, but on dissection of these supposed roots, she found that they were branches which crossed the root.

The root consists of the caudex, stock or main body, and of the radicules or fibres which arise from the caudex, and are the organs by which the moisture is immediately imbibed.

In botanical terminology, we generally consider all that part of a plant which is under ground as the root; but Linné comprehends under his definition, what we term the body or trunk of the plant; and he went so far as to call the stems of trees "roots above ground," but as Dr Smith justly remarks, this seems paradoxical and scarcely correct. Dr Smith adds, that perhaps it would be more accurate to call the caudex a subterraneous stem; although he is rather inclined to think that it has functions distinct from the stem, analogous to digestion; for there is evidently a great difference in many cases, between the fluids of the root, at least the secreted ones, and those of the rest of the plant.

In botanical physiology, by the term root, is often understood the parts only which serve to keep the plants firm in the ground; thus the bulbous and fleshy roots as they are called, are, strictly speaking, not roots; the radicules or fibres being the real roots. The duration of roots is various; they are either annual, biennial, or perennial.

2. The Stems and Branches.—Linné long ago divided the stems of trees into four parts; the rind, the bark, the wood and the pith; and nearly a similar division has been adopted by most vegetable physiologists till the present time.

Mrs Ibbetson (aided by a powerful solar microscope), however, thinks that nature points out a more regular division, a division marked not only by the form, but by the difference of the juices, with which the parts are swelled.

Mrs Ibbetson divides the stem of trees into six parts; 1. The rind; 2. The bark and inner bark; 3. The wood; 4. The spiral nerves; 5. The nerves or circle of life (corona of Hill); and, 6. The pith.

Of the rind.—Mrs Ibbetson conceives the rind to be merely an outward covering to the tree, which prevents its juices from being evaporated by the influence of the sun's heat. The rind is continued under ground; but it may be as useful there to prevent the entrance of the dust and earth, the pressure of stones, or the injury of insects.

The rind is composed of two rows of cylinders, with a single line to divide them. The cylinders are filled with a pellucid liquor. There are seldom more than four or five layers of vessels in the rind; but it is in general so covered with parasitic plants, as powdery lichens, &c. that its thickness is often more than doubled.

The rind does not appear to be necessary to plants in general, as there are many in which the bark serves as a covering in its stead; but it seems to form an essential part of trees.

2. Of the bark and inner bark.—These parts, though certainly different as to form, contain the same kind of juice; and being so nearly allied, may be treated of as one. From the bark and inner bark the leaves take their origin, as will be shown when we come to treat of the formation of the leaf-bud. Mrs Ibbetson conceives that the juice of the bark is the blood of the tree.

In the bark alone are produced the gums, the resins, the oil, the milk, &c.; in short all that belongs to the tree; gives taste to it; all that makes one plant differ from another, and all its virtues, if the expression may be used. The bark is generally green; the inner bark white, yellow, or green. The former consists of vessels crossing each other; the latter of bundles of vessels of two sizes. The large vessels consist of broad cylinders, having a bottom with a hole in it, through which the liquid passes, though not with perfect ease.

Mrs Ibbetson says that on exposing several pieces of the inner bark to the solar microscope, the moment she turned the light on the specimen, the juice, which had before proceeded up the pipe rather slowly, was suddenly propelled forward with a force truly astonishing.

When the heat and light were increased by causing the focus of the rays to fall on the vessels, the side divisions of the vessels were broken through, thus inundating the specimen; but when a proper degree of light and heat was kept up, it was curious to observe the liquid passing from pipe to pipe, in one regular and easy flow, making only a short stop as it issued through the straitened apertures at the bottom of the vessels. Mrs Ibbetson has often stood for more than an hour watching the current, (which passes, however, much slower than the sap does), nor could she perceive while the heat and light were on it, that it required any additional expedient to hasten its momentum; but during the cold and darkness of night, she supposes that the pressure of the bastard grain mentioned by Mr Knight, may very likely assist its flow, as it is at night that the bastard grain is pressed against the cylinders.

The bastard grain is found however only in the wood; but the contraction at the bottom of the large vessels of the inner bark, may probably serve the same purpose, the impetus of the current being increased by the lessening of the apertures of the vessels.

The vessels of the inner bark are very thick in proportion to their size, and there is placed in them a peculiar circular body, which resembles a cullender full of holes so small that no liquid could pass them. In viewing the thick juice which runs through these pipes, Mrs Ibbetson observed many bubbles of air, the size of which was increased or diminished according to the temperature; and as their size varied, so was the flow of the liquid accelerated or retarded. To see these vessels well, the specimens may be placed in a basket which is to be fastened in a running stream for some time, or boiled thoroughly, and then thrown into green wax perfectly melted.

Mirebel says that "some plants have the same juices in every part of them;" but Mrs Ibbetson does not coincide with his idea, for she did not find it to be so; though the potent smell of the liquid belonging to the bark often extends to other parts of the plant, yet it generally vanishes if kept separate for a day, or becomes so faint. Vegetable faint in comparison with the real liquid of the bark as to prove that it does not form an ingredient of these parts. Mirbel says that the cylinders of the inner bark are merely vacuities of the ordinary vessels; but Mrs Ibbetson states that they are exactly the same as these vessels, and occupy the same place.

They have a peculiar shape, being unlike any other vessels of the tree, and they perform a particular office.

The vessels of the bark are smaller, and more simple than those of the inner bark, and are divided by a line or two, running longitudinally between them.

3. Of the Wood.—This is a very obvious part. Place the stem of any plant in a coloured liquid, and every vessel which conveys the sap from the earth to the top of the tree will be tinged.

The sap is a thin watery liquor, probably medicated from the earth, in order to become suitable for the life of vegetables.

Mrs Ibbetson supposes that the sap may vary with the soil, though on trial she has never found that change which might have been suspected.

If we make a transverse section of the stem of a tree, two different kinds of layers present themselves in the wood; some running in a circular manner, which timber merchants call the silver grain; and others from the circumference to the centre, which they denominate the bastard grain. Linné long ago believed that one of the circular layers was added to the tree each year. This opinion has often been controverted, and among others by Duhamel and Mirbel; but Mrs Ibbetson has had an opportunity of verifying the accuracy of Linné's opinion. She also observed that the layer was large or small according to the exposure of the tree, and the favourableness of the season: thus in exposed situations, the circles taken as a whole, were much narrower than in trees not exposed. In some trees she noticed only half a circular layer.

Mrs Ibbetson thinks the bastard stripe consists of two lines or strings with a little scale between them; and they appear, from their extreme susceptibility, to be formed of the same leather-like substance as the spiral vessels, which we are immediately to notice.

Mr Knight merely calls them scales; but as he mentions their pressing close (which they certainly do) to the cylinders at night, and during cold weather, it is obvious (whichever of the opinions we adopt) that the bastard grains are capable of supplying the place of the sun's rays, by their pressure.

The wood-vessels are far more simple in structure than those of the bark; they are very narrow cylinders, and the two rows next to the corona are covered by the spiral vessels.

It is indeed difficult to determine the exact extent of the spiral vessels even with the assistance of the solar microscope, for it is by unwinding them alone that they can be known; and their extreme fineness confuses, in consequence of which they have been taken for sap vessels. Neither Mr Knight nor Mirbel was led into this mistake, and Mrs Ibbetson thinks that there can be no doubt that these vessels (formerly so called) are solid strings which hold no liquid.

The vessels of the wood may be best seen in slices of the stems of young trees; and if not very visible when recently cut, they will soon become so if the slices are kept in a dry place.

If the wood-vessels are cut longitudinally and observed with a high magnifier, as soon as the light is permitted to come on the glass, the flow of sap will be accelerated, and with perfect ease will run up vessels so diminutive that to measure them is almost impossible.

A few of the wood-vessels are separated and run with the spiral vessels to each leaf, in order to nourish it, as will be more particularly noticed, when we come to treat of the leaf-bud.

But little of the sap, however, passes off in this way from the principal current, which flows on; its chief purpose being to form the stamen and the pollen appertaining to it, and afterwards to lend its principal aid to the formation of the fruit and seed.

4. The spiral vessels are a quantity of solid strings coiled up into a spiral form. Mrs Ibbetson supposes them to be formed of a leather-like substance, and, as already mentioned, to be rolled round the wood. In this spiral manner they run up the stems of trees and plants of every kind (with a few exceptions), and from thence into every leaf and flower. These spiral cords are singly too small to be observed by the naked eye. They run into every fibre of the leaf, and are fastened to its edges, thus crossing among the vessels in every direction like a spider's web; by which disposition they can draw the leaves in any way that is necessary for them.

The larger of the interior wood-vessels are each supplied with sets of ten or twelve spiral cords, but the smaller of these have only three or four to each.

In the cabbage leaf and in the burdock, the spiral cords may be found in bundles almost as thick as a packthread, but in smaller leaves they are properly proportioned. These spiral cords, Mrs Ibbetson thinks, are the cause of the motions of plants. See PLANT, p. 601, where these cords are called air-vessels.

5. Of the corona or circle of life.—The next part to be noticed is the small circle of vessels situated between the wood and the pith, the importance of which, in the formation of the seed, will be noticed under Impregnation of the Seed; where are also related strong proofs to show that a plant cannot exist a day without the corona, and that if a young plant be deprived of this part, it will not grow again, though it will certainly do so if the plant be somewhat old. It is very curious that almost every botanical anatomist should have figured this part, without giving it a name, or noticing it particularly; and that these anatomists should have attributed all its powers to the pith, which, from the short term of its existence, and its being perpetually impeded in its progress to make way for the flower-bud, can evidently have but little influence. The circle of life, however, has not escaped the notice of Hill, who termed it the corona.

The circle of life consists of rows of little cylinders which have their own peculiar juice, generally of an austere quality. From the corona all branches take their rise, and from it all wood threads grow. The cylinders of which it is composed run up into all flower-buds, but never approach the leaf-bud as is represented by fig. 1 and 2.; when these cylinders enter the flower-bud, they make their way distinctly to each separate flower. flower, forming the pistil, and after depositing in each side the line, which is the first origin of life, they are afterwards impregnated, or acquire the power of giving life by the juice of the stamen, which runs through the same string into the seed.

That the principal vitality of the plant resides in the corona, we think is proved by the experiments and observations of Mrs Ibbetson under Impregnation of seed, and seems to be farther confirmed by the following remarks.

When a branch is cut from a tree, or a tree is torn up, the corona or circle of life is the first part that dies; and if, after a sudden frost, we examine the flowers of a fruit tree, we shall find that neither the calyx, the corolla, the stamens, nor the seeds are hurt, but that the pistils are destroyed. And if we now observe the pistils with care, we shall see that it is the line of life which is decayed, and that this is the first part in which mortification commences. The peculiar liquor of the pistil acquires a blood-red colour, and the vessels which run up to the stigma become black, instead of their natural yellow colour.

If in wood, this line is injured (either by the decay of the bark or other means) the circle will undulate into a thousand forms, for the purpose of regaining a healthy situation in which it may pursue its course.

Mrs Ibbetson, to prove the power of the circle of life, relates the following observations respecting the pea replans.

She had often measured in winter, seven or eight yards of this grass, which appeared perfectly dead; and yet in May or June, she perceived life in it at the most distant end from the stalk. Next spring she took up two of these creeping branches which were much alike; and on dissecting one of them through its whole length, she found in it a collection of little vessels not thicker than a very fine thread.

This collection of vessels had run about half way the length of the branch, which was about three yards.

Mrs Ibbetson having merely opened the cover of the grass, laid it down again, and the little vessels continued increasing till they reached the end of the branch, when they made a stop, and it was perceived that the grass began to thicken; and at the end nearest the roots, the dead part became inflated with juice, lost by degrees its dead appearance, thickened about the joints within, and at last shot forth fresh leaves and fresh roots from every joint.

Mrs Ibbetson has since watched with the greatest care, and found that the fine thread which runs through the grass protected by the dead scale, was the circle of life. When this thread is stopped by the covers decaying, it waits till the season permits the rest of the plant to grow. From what has been said, it is evident that the dead matter may be inflated with a living juice, and live itself again, provided the life near the stem of the plant be not extinguished. Mrs Ibbetson has observed this to happen in many plants, as in hydrangea, in which the stalks apparently lie down and are inflated again, or at least a part of them.

6. Pith.—Linné considered the pith of plants as of equal importance with the spinal marrow of animals; but Mrs Ibbetson thinks this part of but little consequence, and transfers this importance to the circle of life, which she compares to the brain and spinal marrow. She conceives that the pith forms merely a source of moisture for the plant when required. The pith stops with every flower-bud, and begins again to grow as soon as the bud is past; it decreases as the strength and size of the tree increase; it is the only part of the tree which is devoid of vessels; it is merely a net, not a bundle of cylinders, and is commonly of a remarkably splendid or silver white colour.

It has been said that the pith assumes a variety of figures, but Mrs Ibbetson thinks this is a mistake, though she admits a few different sorts.

All young trees and shrubs are provided with pith; but in the progress of their growth they need it no longer, the wood being a good substitute. On the same account, in general, we find no pith in water plants, which have a hollow stem, and rarely suffer from draught.

Linné thought that the pith was the seat of life and the source of vegetation; or in a word, the primary part of the plant. Duhamel considered it as of but little importance at all. Wildenow and Knight concur with Mrs Ibbetson in regarding it as a reservoir of moisture for the young plants; and Dr Smith holds a medium opinion between that of Linné and the other authors just named.

He says "there is in certain respects an analogy between the medulla of plants, and the nervous system of animals; it is no less assiduously protected than the spinal marrow; it is branched off and diffused through the plant, as nerves through the animal. Hence it is not absurd to presume that it may in like manner give life and vigour to the whole, though by no means, any more than nerves, the organ or source of nourishment."

We were somewhat surprised to find that Mrs Ibbetson had not particularly noticed the cellular tissue as a distinct part to be seen in the stems of trees, as it has been long known; we shall therefore subjoin a description of it. It is a succulent cellular substance, generally of a green colour, at least in the leaves and branches. Duhamel long ago called it enveloppe cellulaire, and Mirbel, more lately, tissue herbace.

Duhamel supposed that the cellular tissue formed the cuticle, or epidermis; but this is not very probable, as his own experiments show that when the cuticle is removed, the cellular integument exfoliates, at least in trees, or is thrown off in consequence of the injury, and a new cuticle, covering a new layer of the cellular tissue, is formed under the old one. This substance is very universal, even in mosses and ferns. Leaves consist almost entirely of a plate of this substance, covered on each side by the cuticle. The stems and branches both of annual and perennial plants are invested with it; but in woody plants it is dried up, and reproduced almost continually, such parts only having that reproductive power. The old layers remain, are pushed outward by the new ones, and form at length the rugged dry dead covering of the old trunks of trees. The cellular integument is a part of plants of the greatest importance; for in it the juices of plants are operated on by light, air, &c.

With regard to the branches of trees it has been already noticed, that they derive their origin from the corona; and they are composed exactly of the same parts as the trunks from which they arise.

3. The Leaves.—Mrs Ibbetson has, with the assistance Vegetable anence of the solar microscope, and by great attention to Physiology, this natural process, being enabled to give some new and interesting views on this subject. Her opinion respecting the formation of the leaf-bud is, "That leaves are formed or woven by the vessels or cotton that is generally supposed by botanists (to be) placed there to defend the bud from the severities of winter; that these vessels (or cotton) are a continuation of those of the bark and inner bark in the stem of the plant; that these vessels compose the various interlacing branches of the leaf, which are soon filled up by the concentrated and thickened juices of the inner bark, which form the pabulum of the leaf."

Mrs Ibbetson says the truth of her assertion may be easily seen by dissecting early buds, in which, except two or three, nothing but the cotton-like vessels will be found. She asks then what could be the use of these vessels? and answers, that to put them within the bud to keep the outside warm is against nature, for it is contrary to nature. The leaf-bud in its first state consists of two or three scales, inclosing a parcel of vessels, which appear like very moist coarse cotton, but when drawn out and placed in the solar microscope, they shew themselves to be merely the vessels of the bark and inner bark elongated and curled up in various forms.

These vessels are of three kinds like the bark, &c. First, Three or four short thick ones which appear to grow from the larger vessels of the inner bark, and through which the thickened juice flows, but with this difference, that the holes are not there.

Then there are two smaller sized vessels, which exactly resemble the smaller vessels of the bark.

Mrs Ibbetson has always found the short thick kind of vessels to form the mid-rib of the leaves, and the smaller-sized vessels to compose the interlacing fibres (or vessels) of the other parts of the leaves; and from often comparing the full-grown leaf with the leaf of the bud, she feels the most thorough conviction that the latter takes its origin as above noticed. The pabulum of the leaf which lies between the vessels, is composed of that thick juice which runs in the bark or inner bark of the tree, and which does not exist in any other part of it. The pabulum differs essentially from the sap, and may be called the blood of the tree, as it possesses peculiar properties in different trees; thus it is of a gummy nature in one, of a resinous in a second, and of an oily nature in a third, &c.

Mrs Ibbetson is not certain whether the pabulum both flows forwards and in a retrograde direction; but she is convinced that the greatest part of it is taken up in forming the leaves. The pabulum of the leaf, after the vessels are arranged and crossed, grows over in bladders, making alternate layers with the smaller pipes (vessels), and with the branches of the leaf.

Mrs Ibbetson states, that she does not know any tree which gives a more convincing proof of the formation of the leaves in the bud, than may be seen in the horse chestnut (Aesculus hippocastanum) about the month of November or December.

Several different mid-ribs may be taken out at once from the same leaf-bud, which have an innumerable number of extremely fine silken vessels fastened to or growing up from each side of them. When these vessels have become sufficiently interlaced with each other, the pabulum will begin to grow over them, in form of small bladders full of a watery juice; and then larger vessels will cross over them, which will soon be followed by another row of bladders; and a similar process will go on until the leaf has attained its proper thickness. The leaves thus formed are very small, but when once their shape is completed every part of them continues to increase in size. Fig. 6 represents the leaf-bud of the horse-chestnut, as it was examined by Mrs Ibbetson about the month of January.

Mrs Ibbetson next notices the arrangement of the leaves in the buds of different trees; but we shall consider them by and bye.

The rolling, folding, or plaiting, &c. of the leaf-bud, it is observed, does not merely take place at once; but to complete the process of budding, it appears that this arrangement of the leaves is repeated several times. During this arrangement the bud-leaves are immersed in the glutinous liquor which runs in the bark (and forms the pabulum); and the pressure of the leaves is very great. By this pressure and the rolling, &c. the leaves are completed; so if a leaf be taken from the bud before this process commences, it may be compared to a piece of cloth before it is dressed; for its back will be obscured by the ends of vessels, which, had it remained in situ, would have been all rubbed off, except the hairs which remain on many plants.

We come now to the formation of the edge of the leaf, a curious and beautiful process.

The bud if opened will appear full of the glutinous liquor which forms the pabulum, and the leaves arranged in the manner proper to the particular tree from which the bud is taken. If one of the leaves be taken out, the edges (in whatever manner folded) will exhibit a perfect double row of bubbles, following the scallop of the edge of the leaf; and it will appear as if it were set with brilliants.

Things being in this state, all that is wanting for the completion of the leaf is the formation of the pores, now to be mentioned. Mrs Ibbetson states that in many hundred forming leaves which she exposed to the solar microscope, she had never once been able to see the pores; which she has often observed after the leaves have completely quitted the bud; and she is uncertain whether this is owing to the greater thickness of the young leaf, and its being covered with more hairs than it is afterwards, which obscure or conceal the pores; or whether it be caused by the upper net-work of the leaf growing last. While the upper and under cuticles of the leaf are growing, the edge of it is completing; for the bubbles generally divide, and partly dry up, leaving horny points in their stead. When the edges of the leaves are completely formed, they burst from the bud and assume a different aspect.

The vessels of the leaves (those confined within the mid ribs and side ribs of the leaves) are of two sorts, the spiral, and the nourishing. The spiral vessels are those corkscrew-like wires which surround the two last rows of the sap vessels. The nourishing vessels are the only parts formed of the wood. They convey the sap necessary for the support of the leaves, and run on each side of the spiral vessels.

To prove that she has given a fair and accurate account of the formation of the leaf, Mrs Ibbet- The leaves of such plants are more woody than any Vegetable others, as every one may know on breaking them. In Physiology, such plants also the circle of life may be traced as leading from one flower to another.

Mrs Ibbetson also thinks that all those parts which concur in forming the flower also join in forming the fruit and seed.

Mrs Ibbetson then adverts to the opinion of Wildenow, when he says, "we find in the springing flower, elongations of air-vessels, but we never see the elongations from each particular part, one forming the future calyx, another the corolla, and so forth." "For instance, in the common sunflower (Helianthus annuus), where in an immense large receptacle, numerous small flowers are placed, how should these elongations be able to unfold themselves into florets from the bark, inner bark, &c. through such a receptacle? There would arise a confusion amongst these small parts which is never met with."

"How should, besides, the stamens be formed in herbs, which are not ligneous, or the pistil in plants which have no pith? Every one may thus easily conceive that all these opinions are mere hypotheses, which may be refuted, even without the aid of anatomical dissection.

Mrs Ibbetson attacks Wildenow's opinion, and says that he adduces the syngenesian class to prove the accuracy of it, the class which contains the very plants that would have proved the mistake of his argument, had he dissected them.

Mrs Ibbetson then proposes the following questions to Wildenow. Why, if the nourishment of each part of the stem be not confined to each different part of the flower, does the whole arrangement of the parts alter, the moment it gets to the flower-stalk?

Why are there particular vessels to confine and carry the juice to each peculiar part, if it were not of consequence that this juice should touch no other places? For what purpose is the curious and artificial management in the bottom and top of a seed-vessel, which enables the dissector to say, that "there are five divisions of little vessels proceeding from the wood; I know, therefore (though I do not see it), that this must be a pentandrian flower; here is but one middle vessel proceeding from the circle of life (for the pith stops), it is therefore of the order monogyne; here are five divisions of little vessels proceeding from the inner bark, it must therefore have five petals?"

Mrs Ibbetson wishes others to be convinced of these facts as well as herself. If a cut be made above or below the seed-vessel of a lily, a violet, or a tulip, she thinks conviction of her accuracy will follow. Why in cutting above or below the seed-vessel of a syngenesian flower can you directly tell, whether it belong to the order superflua, equales, or segregata? Look at the bottom of the seed-vessel of the sonchus; every pin hole of the vessel of the male is carried up by corresponding vessels in the outward cuticle of the seed, till it meets and joins the ligature of the males; and the female liquor is protruded through the inside of the seed, and is perhaps one of the strongest proofs of the impregnation of the female. In the syngenesian class (see fig. 12.), the delicacy of the vessels, which may be supposed too small for a liquid to flow through them, must not impede the belief that it does so, when we consider... Vegetable side the circulation of blood in the diminutive animal Physiology that torments the body of the flea or louse. Mrs Ibbetson says she has seen the liquor run up with the utmost celerity through the upper cuticle of a very small seed of a plant belonging to the syngenesian class, till it met the male and continued its course. It is to be understood that the juice from the corolla flows in the rest of the cuticle, and that the largest vessels are those for Fig. 12. 13: the male liquor. See figs. 12, 13.

II. Physiology of Plants.—In treating this part of the subject, we propose to consider, first, the impregnation of seeds, and, second, the irritability of vegetables.

1. The impregnation of the seed.—The investigation of what is included under this title, forms one of the most beautiful and interesting pursuits of the vegetable physiologist. Mrs Ibbetson has communicated some curious observations on this subject. Provided with a powerful solar microscope for opaque objects, she proceeds to an examination of the seed, and the first shooting of the infant plant, or rather of the germ or vessel which precedes it; and she remarks that it is almost impossible to ascertain the exact time when the seed is first formed in the pericarp; but that she has always found it in the winter buds when they were large enough for dissection.

It is curious to observe the vessels, which, she says, may properly be called the life, tracing their way to each flower-bud: for a seed may be said to depend for perfection on two separate moments: the one in which the life first enters the seed, when the whole outward form appears to be perfected; and the second, when the impregnation of the seed takes place, by the ripening of the pollen.

But when the life enters, it leaves a little string, and remains for a long time afterwards in a torpid state. This string crosses the corolium, or heart of the seed, so called because it is the cradle of the infant plant. She then states that the seed is attached to the seed-vessel by two distinct organs, termed by the first botanists the umbilical cord, but as she thinks improperly, since they do not convey nourishment to the infant plant, which is wholly the office of the second set of vessels.

We cannot agree with Mrs Ibbetson in her opinion; for although the umbilical cord of an infant contains nourishing vessels, it also contains nerves, and yet we would never think of restricting this term alone to the arteries. The first of the connecting organs Mrs Ibbetson conceives to be the circle of life, first, because without it the plant dies, and, second, because although every other part be eradicated by degrees and the circle of life be uninjured, the plant will grow again.

She has made these experiments many thousand times and with the above results. The circle of life consists of delicate simple vessels, which carry a juice of a particular nature, and may be traced in every part lying between the wood and the pith. These vessels are not to be found in the leaf-bud; for they pass by it to the female flower, where they establish a new life in the seed: a life which will enable it to grow, but not to give life without impregnation. These vessels are the life, therefore, from which all flower branches grow and all root-threads proceed. In calling these vessels the circle of life, Mrs Ibbetson says she only expresses what its office seems to denote.

Mrs Ibbetson goes on to describe the next (or second) organ by which the seed is attached to the seed-vessel. It consists of the nourishing vessels, which she is inclined to think proceed from the inner bark; at least they may certainly be traced thence after the infant plant has left the seed. When introduced, they enter not the seed at the same place as the life does; they come not into the corolium, but pass it, and spread themselves over a small spot below it, which is visibly of a different nature from the rest of the seed. In farnaceous plants this spot is yellow, and yields a milk-white juice; but in other seeds it is white, and gives a glutinous water of a sweetish taste. Mrs Ibbetson thinks it probable that the nourishing vessels come from the fruit filled with this juice, which medicated with that part of the seed (which very apparently dissolves), they together form a nourishment suited to the infant plant. When the seed is so far perfected, it remains in an almost torpid state, or growing very little; while the flower expands daily, and the stamens are hastily advancing to enough their perfect state.

It is now that by an almost imperceptible contraction of the lower part of the pistil, the juice is raised to the stigma (A), on which it may be seen hanging in a large glutinous drop, which never falls off. As soon, however, as the mid-day heat abates, this juice, which is peculiar to the pistil, retires again within the tube, the contraction ceasing with the heat that caused it. The same process goes on daily, till the stamens are ripe and ready to give out their interior powder to the pistil, which is always so placed as to receive the greater part of it; and as the anther (B) requires only moisture to burst it, it soon yields that fine and imperceptible dust, which quickly melting and mixing with the before-mentioned liquid, forms a combination of so powerful and stimulating a quality, that it no sooner runs down the interior of the style, and touches the nerve of life in the heart of the seed, than this vessel shoots forth in the most surprising degree, forming directly a species of circular hook within the void; which in less than two days is often completely filled, though it had perhaps for many weeks before lain in an absolute torpor. This circular nerve is soon covered by an excrescence that hides it; but if the corolium be divided with a fine lancet, the circular hook is discoverable, until the young plant is near leaving its cradle or seed. At the turn of the hook the cotyledons grow, and the root shoots from the covered end. The plant may be now said to lie in the seed in a contrary direction from that in which it will at a future time grow, since the root is above, and the stem below: but nature has provided for their change of place, since it is effected as they leave the seed. It has been already noticed that the nourishment of the infant plant

(a) In the journal it is said "to the pointal;" but certainly stigma is meant, for pistil and pointal are synonymous.

(b) In the journal it is called pollen, but anther must be meant. plant is medicated between the juice brought in the nourishing vessels, and the peculiar spot in the seed, forming a liquid which continues to abound; indeed the infant plant may be said to repose in it, till the root has opened the whole or part of the seed. The root then changes its direction, and runs into the earth, soon forming a number of stringy hairs, which serve as so many suckers to draw the liquid nourishment from the earth, while the plant quickly shows, by the rapid progress it makes, the advantage it receives from its change of diet; for it soon raises itself from its prostrate posture, emerges from the seed, and is now seen in its proper direction. The above account, we think Mrs Ibbetson justly remarks, affords a complete confirmation of the sexual system.

In the syngenesian orders, the pistil being mostly single, runs up from the seed; and the juice of the pistil has no other way of reaching the pointal (stigma must be here meant), but by passing through the seed, which it does without producing any effect, or filling up the vacancy at the top of the corculum. But as soon as the juice of the pistil becomes mixed with the pollen, which dissolves in it, the void of the corculum is filled, the hook is soon afterwards formed, and the plant is roused to life. Mrs Ibbetson relates some experiments which she made to ascertain whether the umbilical cord was, or was not, the life of the plant. She placed a bean in the earth, and when the infant plant was ready to leave the seed she opened it with a fine lancet, and cut off the cotyledons, just where they join the heart and the circular hook which have been before described. She then tied a piece of very fine thread round the bean, and replaced it in the earth. The cotyledons grew again, though higher up, but they appeared very weak and sickly for some time. She cut off the root of another bean which had been placed in the earth, and which was of the same age as the above, and found that the root grew again in a few days and appeared quite healthy.

In a third experiment she separated and cut off the nourishing vessels from each side of the bean; but a great number of hairs grew from the wounded part, which, by attaining moisture from the earth for nourishment, supplied the place of the vessels cut off; so that it was not ascertained whether or not the bean would live independent of these vessels, which was the object of the experiment. We observe here, however, a grand provision of nature for the embryo plant: hairs being formed to supply it with moisture when the nourishing vessels are destroyed. Mrs Ibbetson next took a bean which had been about four days in the earth, and opening it with great care took out with a fine lancet the part which she esteems the cord of life, that is, the part which crosses the corculum and shot forth on the first impregnation of the plant. oo, fig. 14. and 15. represent the nourishing vessels of a bean; L to n two seminal leaves or cotyledons; ll the cord of life, which is more easily seen in the seed of the lily, fig. 15. ll crossing the empty part of the corculum. Mrs Ibbetson took a flower of the lilium genus, as having a large vessel easily attained; and being careful not to separate it from the nourishing vessels, she divided the line of life fig. 16. ll, cutting each thread between the seeds, and so cutting off their communication; but did not touch Vegetable Physiology.

The consequence was, that the seeds of this flower were never impregnated. Mrs Ibbetson next tried the effect of taking the nerve of life from the chestnut, the walnut, acorn, &c.; first opening a seed without touching the nerve, that she might be certain that the opening was not the cause of its death. Fig. 17. represents Fig. 17. the heart taken out of a seed of the chestnut; l is the circular hook already described; oo the nourishing vessels, and ll the line of life, which was taken out from some seeds where it crosses the heart at m. Fig. 18. Fig. 18. is the seed of the gooseberry; oo the nourishing vessels, ll the line of life, and m the corculum or heart.

She found that all those seeds from which she took the nerve of life died; and that the others, which had been merely laid open, lived. She remarks that it is only at the beginning of life, that the plant can be killed by this process; for when older, if the nerves of life decay, they shoot out above the declining part, and run into any part of the stem that is pure, to preserve themselves. Mrs Ibbetson then states that this nerve is the source of life in very decayed trees; and is also the cause of a double pith, or at least the appearance of it, in many trees.

To observe this line of life, seeds must be examined in their first formation; for when it has done its office, it detaches itself. When the seed is boiled, the line of life and nourishing vessels mark themselves by becoming of a dark colour.

2. Irritability of vegetables.—In entering upon this subject, we ought to warn our readers, that very opposite opinions have been entertained respecting it; some physiologists of the greatest eminence allowing that we have satisfactory proofs of the irritability of vegetables in a variety of plants, but more particularly in the motions of the mimosa, dionea, &c.; while others of no less respectability ascribe these motions to the influence of light, heat, or some other mechanical agent.

As neither muscles nor nerves have ever been demonstrated in the vegetable structure, of course the proofs of the irritability of vegetables are drawn from the intimate analogy which seems to exist between the motions of some plants and those of animals. Some physiologists, from observing the similarity of motions in the two kingdoms, were naturally led to ascribe them to the same cause; others, from not being able to observe the same motile organs, namely, muscles, in both kingdoms, denied that plants could possess irritability; a third set, wavering the idea of irritability in the vegetable kingdom, have laboured to show that the motions of plants depend on mechanical causes alone.

We shall first notice the observations of Mrs Ibbetson, who ascribes the motion of plants to the spiral wires which we have described. Her opinion is founded upon a number of new observations made with the solar microscope, which we shall proceed to relate.

1st. The spiral vessels are not to be found in any plants to which motion is unnecessary.

She could not observe these vessels in any of the fires, in any of the plants which spread their leaves upon the surface of the water, in any of the sea weeds (c), of the lichens, or of the grasses; and she does not think that

(c) She afterwards excepts the confervæ, which have motion. Vegetable that they exist in the scolopendrums or lemnas. We would here observe that if these observations were completely true, they would certainly afford a strong proof in confirmation of her opinion; but we suspect that they are not altogether just, especially as we observe a discrepancy in the papers of Mrs Ibbetson. Thus at one part she has given us a very minute description of the spiral vessels in the runners of the poa reptans, and now she says they are not to be found in the grasses (D).

Mrs Ibbetson's second argument is, that if a plant whose leaves present their faces to the light, be turned so that the backs are to the sun, the leaves in a few hours will regain their former position; but if this be often repeated, although the plant will not suffer, yet the leaves will be longer at every repetition in returning to their former situation, or will cease to move at all. She accounts for this by saying, that the spiral-like elastic vessels are relaxed by the operation, and lose their power of coiling into their usual form.

Others would account for the above fact by saying that the irritability of the plant was exhausted by these repeated and unnatural actions; in the same manner as the mimosa becomes gradually less sensible to impressions when too often renewed.

Mrs Ibbetson's third argument is, that those leaves which have most motion, are provided with most spiral vessels, and have these vessels most twisted; as in the populus tremula.

Fourth proof. Mrs Ibbetson divided the spiral vessels of a vine leaf while growing, without touching the nourishing vessels; and from that moment it never contracted, and when placed with its back to the light, it did not alter its position, though it was long before it decayed. Both electricity and galvanism cause these leaves to contract, by affecting the spiral wires (not the cuticle), for when the leaf is deprived of these vessels it does not contract at all.

We would here remark that we suspect much, in the above experiment, that more than the spiral vessels was divided: at any rate there is very great discordance between Mrs Ibbetson's experiments and that of M. Calandrini, who found that vine leaves turned to the light when they were separated from the stem and suspended by a thread.

Fifth argument. Mrs Ibbetson observed, when she placed some of the spiral vessels taken from a cabbage leaf upon one end of a long netting needle, and caused a candle to approach, that they were much agitated, and at last flung themselves off the needle. We think no conclusion can be drawn from what is here stated.

The fresh water conferens and the dodder tribe, are the only plants, without leaves, that Mrs Ibbetson is acquainted with, which have spiral vessels.

Mrs Ibbetson says that the spiral vessels are so very tough, and so very tightly coiled, in the leaf stem (petiole) of the geranium cordifolium, that she has by means of them been enabled to draw up the leaf; but it is difficult to be done.

The sixth proof is drawn from the effect produced by moisture on Captain Kater's hygrometer, which will be noticed soon.

General Observations.—Mrs Ibbetson says the spiral vegetable wires may be considered as a secondary cause of motion, as they are primarily acted upon by light and moisture. By means of the spiral wire, all the movements of plants are made; by it, flowers open in the morning and shut in the evening; the leaves turn, and the creeping plants wind in their regular order. Mrs Ibbetson says, the opening of the flower at a different time of the day, or its turning in a different manner, does not militate against the above statement; as strong light and dry weather produce a contraction of the wire, while darkness and moisture effect a dilatation of it. It depends wholly upon the position in which the spiral wire is placed, whether by its dilatation the flowers shall be opened or shut, as in mechanics the same spring may be made to turn to the right or to the left, to open or to shut a box. Most of the flowers which Mrs Ibbetson has observed to close at noon, have an extremely limber corolla, formed only of a double cuticle without pabulum; and hence they are soon overcome by heat, and relaxation directly takes place; as in the convolvulus nil, the evening or tree primrose, &c.

We must add, however, that we regard this account of the spiral vessels with some degree of doubt. We suspect that the spiral vessels, if they have the power of opening or shutting a flower, will always act in one uniform manner; i.e. if they are able to open it, they will always do so, and vice versa.

The nymphea alba raises itself out of the water, and expands, about seven o'clock in the morning; and closes again, reposing upon the surface, about four in the evening. Now its petals are much thicker than those of the leontodon taraxacum, which shuts up its flowers between eight and nine in the evening.

We could multiply instances; but we conceive we have said enough to shew, that the flowers with the most slender corolla are not uniformly those which soonest close.

Mrs Ibbetson says, contrary to the opinion of Mirbel, that the case in which the spiral vessels are inclosed is capable of being stretched; indeed it is formed of so thin (or rather so loose) a substance, as plainly to be intended to dilate and contract. The case is composed of a very few thin vessels, interlaced with an extremely fine spiral wire; while the large spiral vessels fill up the case in an irregular manner, the nourishing vessels form a regular circle of tubes around it. See fig. 29, and 30.

Of the Indian grass (andropogon contortum of Liné), of which Captain Kater's hygrometer is formed.—The chief part of it is made with the spiral awn of an Indian grass, which readily untwists in a moist atmosphere, and vice versa. Now Mrs Ibbetson asks, if the most trifling change of moisture can untwist one sort of vegetable fibre, and by this means manage an instrument, why should not a quantity of similar formed fibres or spiral vessels produce the same effect on leaves and flowers? She says, Captain Kater's hygrometer moves very sensibly if a finger be placed within half an inch of the fibre (awn.) Now, the most sensitive plant we have will not move but with the touch."

We are quite aware of the effects of moisture on some vegetables.

(D) She found the spiral vessels also in the andropogon contortum. We have strong proofs of it in some of the mosses, as in the *bryum hygrometricum*, which, if the fruitstalk be moistened at the bottom, makes three or four revolutions; if the upper part be moistened, it turns the contrary way.

We can scarcely compare these motions with those of the mimosa; for it is quite evident that they are produced by moisture: but as we are to speak of the motions of the mimosa in a little, we would only observe, that when Mrs Ibbetson says "the sensitive plant will not move but with the touch," she argues against herself; for this shows that it is acted upon by the same causes as animal muscles, and that it is not governed by moisture alone.

The only sensitive part of the Indian grass is the awn, which is formed of a leather-like substance, infinitely thicker and stronger than the usual spiral vessels in plants. The awn is formed of two apparently flat pieces, with a cylindric hollow running through the middle, which is filled with a thick spiral wire. Fig. 21, 22, 23, and 24. Each side of the awn is bristled; but the bristles do not add to its sensibility.

Of the Nettle.—The awn or sting of the nettle is a long pipe with a bag at the end divided into two parts; the smaller contains the poison, and the larger is situated below it. This bag seems also to be composed of a leather-like substance, and it is likewise affected by light and moisture.

The moment the upper part of the pipe is touched, the under part of the bag whirls up, breaks the poison bladder, and throws its contents violently up the pipe, burning the person who touches it.

Light thrown upon the bag by means of the solar microscope, produces the same effect as touching it. The poisonous liquor is protruded up the pipe with great force, till it issues out at the minute aperture at the point; but before it does so, the pipe is bent down with a jerk, by means of the spiral wire.

The spiral wire winds round the bag at the bottom of the pipe; and it is by the action of this wire that the bag is made to contract. The nettle lays down its stings every evening, just as the sensitive plant does its branches. See fig. 19, and 20.

*Mimosa Sensitiva.*—The motions of this plant are regulated not only by the spiral wire, but also by a bag of a leather-like substance, which is capable of contraction and dilatation.

We shall next give Mrs Ibbetson's plate respecting the structure of this plant, with her description.

Fig. 25, is a representation of the springs which govern each leaf; d, d is the stalk. Each leaf has a base e, e, which serves to concentrate the spiral wires. These passing over in every direction, being drawn through the narrowest parts of the stem b b b b, press the stem together; and, when touched, lay the leaves, one on the other, the whole way down the leaf-stalk. But, before the stimulus is applied, the stem is flattened in a contrary direction. The ball of the leaf is hollow and filled with oil. The parts e e and p p (fig. 26) are made of that leathery substance, which forms the cuticle, and is contracted by the light in the solar microscope. The parts e e contain the oil which serves to lubricate the knots (we suppose), and enable them to slip over each other; beside, probably, acting some important part in the formation of the various gasses and juices in the composition of the plant.

When touched, the whole string relaxes at o o, and lets the branch fall. This it would also do at m, if it were not supported by the wood-vessels turning into the leaf. Fig. 27, is the part e c p p uncut, and in its natural state. Mrs Ibbetson thinks that not only the motions of this plant, but of all others, depend upon the spiral wires which contract and dilate by the action of light and moisture. She adds, that there are no spiral wires in the seminal leaves of the *mimosa sensitiva*, and that the seminal leaves have no motion whatever.

In farther illustration of this subject, we shall next present our readers with some observations by Mr Lyall, lately published in Nicholson's Journal, respecting the irritability of the *mimosa pudica*, and some other plants.

"It is well known (he observes), if we take a leaf of this plant, similar to what is represented (fig. 31.), and then, by means of a pair of scissors (completely dry), cut off half the pinnula A, this pinnula will contract at its joint, either immediately, or in a few seconds; its neighbour, or opposite pinnula, B, closing at the same time, or soon after.

"The pinnula A and B having come into contact, there is a pause, or a short cessation, of motion; but in the course of a few more seconds, the next pair of pinnulae, CC, will also shut up, and the same will happen with every pair of pinnulae of that pinna successively; only with this difference, that the intervals between the shutting up of each pair of pinnulae will be shorter, the farther it is from the pinnula that was cut. After the whole of the pinnulae of this pinna have completely closed, and a little interval, then the joint D will bend so as to allow the pinna to drop considerably.

"Nevertheless, the motion is often not so obvious in this joint, as in that to be mentioned.

"A longer pause will now intervene, in some cases so long as to make us suppose that all motion is at an end; but at length the joint E suddenly bends, and astonishes the beholder.

"The petiole F now, instead of forming an acute angle with the stem above the joint, forms a very obtuse angle with it.

"We shall now have another cessation of motion, and then the joint, H, will slightly bend; then another pause, then a shutting up of the pair of pinnula, H, and so on with the other pinnulae, till the whole pinna is closed. The motions, however, will not be so regular in this pinna as they were in the other; for as the pinnulae II approach, they press forward the next pair, and so on with all the rest."

These motions, the author supposes, are not occasioned by impulse; for a bit of the pinnula may be cut off almost without producing any motion.

But, allowing that a little motion were produced, it comes naturally as a question, Why does the motion become so extensive? how is the impulse communicated to the origin of the petiole? The author does not think that these questions will ever be satisfactorily answered upon mechanical principles.

He admits indeed, that a structure exists in the *mimosa sensitiva*, corresponding to what Mrs Ibbetson has described; Vegetable described; although he seems to have some doubts respecting it. He then proceeds to inquire, whether by such a structure, acted upon by heat, light, or moisture, we could possibly explain the motions of the mimosa pudica. "On the experiments above related, (he observes,) I presume no one would say, that moisture was the cause of motion, as the scissors were quite dry."

It is to be remembered also, that this plant will perform its motions under water.

As there was no change of light, consequently this had no share in the effect. Besides, when moisture is produced (Mr Lyall certainly means darkness) in consequence of the abstraction of light, all the pinnae shut up at the same time; not, however, in the regular order mentioned in the experiment. Neither does the motion take place from change of temperature, for the temperature was not altered.

A great many questions will here suggest themselves, as, How does it happen that the motion is produced? how does it become so extensive? how comes it that there are regular motions and pauses, &c.?

The author concludes, by saying, that it is vain to attempt any mechanical solution of the phenomenon mentioned above, "which would seem to depend on an exquisite irritability in the plant itself."

Dionaea Muscipula.—Mr Lyall does not think that the motions of this plant are to be explained in the manner spoken of by Broussonet, who ascribed them to the evacuation of a fluid from the leaf, which will be noticed when we speak of the droserae. For the leaf may be touched without causing any efflux of fluid whatever, and yet it will contract completely.

Comparetti's explanation respecting the motion of this plant is not admitted; because it seems improbable, is contrary to analogy, and inadequate to explain the phenomenon.

Of the Drosera Longifolia and Rotundifolia.—As many of the muscles of the animal system, as the heart, diaphragm, &c., act quite independent of the will, and as these parts are highly irritable, Mr Lyall wishes to show, that a voluntary command of a muscular force should not be taken into the definition of the word irritability, as has been done by some. Mr Lyall says, "By irritability, I understand, that property inherent in some bodies (or rather parts of bodies), by which, when a stimulus is applied, they are enabled to contract.

The leaves of the drosera rotundifolia, when properly unfolded, lie round the stem in a stellated manner. The footstalks of the leaves vary in length from half an inch to an inch and a half. The leaves are covered on their upper surface by a number of hairs, varying also in length from one line to three-eighths of an inch, and are each terminated by a little gland, which, gland is covered by a transparent viscid fluid, presenting a fine appearance.

The chief difference between the drosera longifolia and rotundifolia is in the shape of the leaves; those of the former being obovate, while those of the latter are of an orbicular shape.

Mr Lyall mentions the observations of Mr Whately, who, it would appear, was the first in this kingdom who described the contractions of the droserae when irritated.

Mr Whately and Mr Gardom had observed some insects imprisoned in the leaves of this plant, and hence were led to press with a pin the centre of other leaves in their natural and expanded form, when they very suddenly contracted, and, as it were, encircled the pin.

Roth had noticed, in 1779, that the leaves of the droserae moved, when irritated. He placed an ant upon the middle of a leaf of the drosera rotundifolia, but so as not to disturb the plant. The ant endeavoured to escape, but was held fast by the clammy juice of the points of the hairs, which was drawn out by its feet into fine threads; in some minutes the short hairs on the disk of the leaf began to bend, then the long hairs, and laid themselves upon the insect. After a while the leaf itself began to bend, and in some hours the end of the leaf was so bent inwards as to touch the base. The same happened when the experiments were made on the drosera longifolia, but more rapidly.

Roth also found that the hairs bent themselves when he touched them with the point of a needle, with a hog's bristle, or when he placed a very small piece of wood the weight of an ant upon the leaves.

Mr Lyall next gives us an account of his own experiments. He says, "that for five months, he almost every day, had the species of droserae under his eye, either at home or in the country;" and he confesses, that he never saw such a rapid contraction of the leaves of the drosera rotundifolia, as had been noticed by Messrs Whately and Gardom: but in all his experiments the contraction was gradual, though it seldom failed to happen, if the plant was in good condition. In most of his experiments an hour was necessary for the complete bending of all the hairs; and it required some hours for the perfect shutting up of the leaves. Hence it is evident, that whoever has a wish to notice the motions of the droserae, must not set out with the expectation of seeing a rapid motion, similar to what happens in the mimosa, follow the application of a stimulus; but, to observe the ultimate effects, must watch with an attentive eye, for at least 20 minutes.

In accounting for the manner in which these motions are performed, various opinions have been held. Broussonet suspects that the disengagement of some fluids influences them. He says, that the insect, by absorbing the fluid which is on the points of the hairs, empties the vessels of the leaf, which folds upon itself; and the quickness of the action is proportional to the number of hairs touched by the insect.

Our author observes, that "this theory, at first sight, does not appear even to be plausible; for, how is it possible that an insect can absorb a thick tenacious fluid? No doubt, however, part of this fluid will be attached to the part of the insect which touches it; but this seems quite unconnected with the contraction of the leaf. On the 30th of July, Mr Lyall brought from the country a number of plants of the drosera rotundifolia, and, on inspecting them, he found many of the hairs of the leaves deprived of their viscid fluid; but yet both they and the leaf remained quite expanded and in good condition. Next day, about four o'clock, he placed a small bit of sulphate of copper, in the disk of one of these expanded leaves, and by six o'clock most of the hairs on one side of the leaf, even the outermost, had bent themselves over the bit of copper; this seems Vegetable to prove the inaccuracy of Broussonet's theory. In other experiments, he placed small bits of bread or wood, or three or four of the central hairs, without touching the other hairs, or the viscid fluid on their ends; and in a few hours he found that all the hairs had contracted around the foreign body. In some plants, the sulphate of copper was placed upon some of the small hairs in the disk of the leaf, without touching the leaf itself; yet the bending of the hairs and leaf was complete.

"We have here proof (he adds), 1st, That the leaves do not contract when deprived of their viscid fluid, which ought to have been the case if Broussonet's theory had been true. 2ndly, That the contraction takes place even when the viscid fluid does not cover the little glands. 3rdly, That the contraction follows, although the foreign body is not brought into contact with all the hairs.

The opinion of Sennebier, who appears to have ascribed the motions of the drosera to the effect of pressure is next examined. "Sennebier seems (it is observed) sensible, that the contractions of the leaves take place even when light bodies are placed on them, which circumstance of itself would lead us to suspect, that pressure is not alone the cause.

"I know (it is added), that, if we press on the centre of a leaf with a pin, &c. we may cause its margin to approximate the pin; and this certainly would be owing to a mechanical cause. But, suppose we see the contraction take place, as I have done, when a body specifically lighter than the leaf itself is placed in the centre, as a bit of rotten wood; should we be still inclined to ascribe it to a mechanical cause? Admit that it is the case. Suppose, then, we place the same bit of wood on the margin of the leaf; what effect ought to follow? If it were owing to a mechanical cause, or the weight of the foreign body, as in the last mentioned case, then we should expect, that the part of the margin of the leaf, on which the bit of wood rested, would be depressed; which undoubtedly is not the case: but, on the contrary, the margin rises, and then contracts towards the foreign body, or towards the footstalk of the leaf.

"That this motion does not depend on pressure, may be still better illustrated, by placing a fly, or some other body, on the apex of a leaf of the drosera longifolia. The hairs near the foreign body will contract around it, and then the apex of the leaf will rise upwards, and turn inwards, until it touches the base. Or, if the offending body is small, the leaf will become convoluted around it."

From the result of his experiments, the author thinks, that the motions of the leaves of the drosera cannot be explained on mechanical principles. He conceives, that these motions are performed, if not by muscles, at least by something which is equivalent to muscles in the animal body.

It appears that the leaves of the drosera rotundifolia and longifolia remain completely expanded during the hottest sunshine and driest weather; during the coldest and wettest weather; during the greatest darkness, and, finally, during the brightest light of day. This, however, is to be taken in a limited sense, i.e. only during the expansion of the leaves, not during the cold of winter. "Here, then, neither heat, cold, dryness, dampness, darkness, nor light in general, at all affect the leaves; but, if a foreign body be applied to the leaf so as Vegetable to stimulate, then it will shut up" in the manner we have already described. See Vegetable Anatomy, Supplement.

EXPLANATION OF PLATES DXLI., DXLII., AND DXLIII.

[Note, that some errors in the references to figures in the text may be corrected by this explanation, which is accurate.]

Fig. 1. Part of a branch, shewing the manner in which the line of life, c e, enters into the flower-bud, a, and passes by the leaf, b b.

Fig. 2. A flower-bud, showing the line of life, c e, running up to each flower, a, a, a, a, a, a, a, a, and the pith terminating at b.

Fig. 3. Section of the stem of a tree; a, the rind; b, the bark; c, the inner bark; d, the wood; e, the spiral nerves; f, the corona or line of life; g, the pith; h, h, the silver grain; o, o, o, the bastard grain.

Fig. 4. Cylinders of the inner bark.

Fig. 5. Cylinders of the wood.

Fig. 6, 7, 8, 9. Commencement of the growth of leaves, exhibited in different stages. a, a, a, a, The mid-rib; b, b, b, the young vessels appearing like cotton; c, c, the spiral nerves; d, the smaller vessels crossing each other. Fig. 9, also shews, c, c, the fine vessels growing up each side of the mid-rib; and f, the pabulum.

Fig. 10. Leaf-bud of the lime-tree.

Fig. 11. Leaf-bud of the horse-chesnut about January.

Fig. 12. A seed-vessel of the class syngenesia; a, the calyx; b, female florets; c, male and female florets.

Fig. 13. Section just above the seed-vessel of the dianthus. a, the calyx proceeding from the bark; b, the corolla, from the inner bark; c, c, c, ten stamens from the wood; d, the seed-vessel; e, the pistil from the corona or circle of life.

Fig. 14. Representation of the bean. o, o, the nourishing vessels; L to n, the seminal leaves, or cotyledons; l, to l, the embryo.

Fig. 15. o, The nourishing vessels; l, the embryo in the seed of the lily, crossing the empty part of the corculum.

Fig. 16. Shews, l, l, the line of life; o, o, the nourishing vessels.

Fig. 17. Represents the heart taken out of the seed of a chestnut. l, the circular hook; o, o, the nourishing vessels; l, l, the line of life, which was taken out where it crosses the heart at m.

Fig. 18. The seed of the gooseberry; c, the nourishing vessels; l, the line of life; m, the corculum or heart.

Fig. 19. The sting of the nettle, as viewed with the solar microscope; x, the bag of poison; x, the spiral wire.

Fig. 20. The sting after the poison has been thrown to the point; x, the spiral wire contracted.

Fig. 21. Indian grass greatly magnified, showing the manner in which it is formed.

Fig. 22. Awn of the grass.

Fig. 23 and 24. The grass twisted.

Fig. 25. Leaf of the mimosa sensitiva.

Fig. 26. A longitudinal section of the leaf-stalk of the mimosa sensitiva, the middle part containing five cases of spiral wire, and each extremity only three. Fig. 27. The extremity of the uncut leaf-stalk, which is divided at p.p in fig. 26.

Fig. 28. A horizontal section of the stem of the mimosa.

Fig. 29. A case full of the spiral wire much magnified.

Fig. 30. Spiral wire still more magnified.

Fig. 31. Leaf of the mimosa pudica.