The provinces of Anatomy and Physiology may now, we believe, be looked upon as distinctly and permanently defined. Anatomy is understood to treat solely of the Structure of Living Bodies, and Physiology solely of their Functions.

We shall observe this arrangement strictly in the following article. It is one which, in our opinion, has already been productive of material advantages to the science of Vital Economy. The descriptive detail of the structure of Living Bodies is no longer distracted and obscured by superficial and unconnected views of their functions; nor their functions carelessly discussed, in the form of occasional and uninstructive commentaries on the descriptions of their structure. Each is made the subject of separate and particular investigation; and not only has

ANIMAL ANATOMY.

I. HUMAN ANATOMY.

1. In our supplementary remarks on this first and most important department of Animal Anatomy, we shall endeavour, by the arrangement we intend to follow, to exhibit the outline of a plan better adapted, we conceive, for an elementary view of the structure of the Human Body, than that which has usually been observed in the schools of medicine, or in anatomical works.

But it will be necessary to premise a few observations on the acceptation of certain terms, which will occur very frequently in the descriptions that are to follow.

2. By the period of impregnation or conception, is uniformly meant the moment at which a child, or infant-being, begins to be formed within the womb of the mother.

While the child is yet retained within the womb, it is denominated a fetus or embryo; the term embryo, however, being chiefly applied to it in its earlier stages.

The end of the ninth month after conception, which is the natural period of birth, is often denominated the full time.

The inhabitants of Great Britain, and perhaps of Europe in general, are usually full-grown, or adult, at the age of twenty-five or thirty years. This is the

ANIMAL.

Anatomy, period of life, therefore, which we wish to be understood as denoted by the term adult age, or maturity.

Our descriptions are to be considered as applicable to the adult male, unless when the contrary is expressly specified.

To regulate the interpretation of the terms above, below, before, behind, &c. we shall uniformly suppose the body to be in the erect posture, with the arms hanging parallel to the trunk, and the palms of the hands, and the toes, turned directly forwards. This is a simple remedy, and the only effectual one, for the trifling ambiguity which might otherwise attend the use of these terms.

Any part of the body, or the surface of any part, which is capable of being divided, in one or more directions, into two portions or halves exactly alike, is said to be symmetrical; and the line or plane separating them is called the median line, or median plane.

PART I.

OF THE EXTERNAL FORM, STATURE, AND WEIGHT OF THE BODY.

External Form.

3. There are very few anatomists who enjoy opportunities of ascertaining the gradual changes which take place in the external form of the fetus during the earlier periods of its development. The admirable series of engravings, therefore, in which Soemmerring has represented these changes, from the first to the fifth month after impregnation, will be consulted with great interest. (See Icones Embryonum Humanorum.)

An embryo of three or four weeks appears in these representations to the naked eye, somewhat like a mustard seed just beginning to grow; the head being like the body of the seed, and the trunk and remaining parts like the radicle. With the magnifying-glass, however, a little dark circle can be distinctly seen in the regions of the eyes, and a small slit, corresponding to the orifice of the mouth. Four little prominences are observable on the trunk, in the situation of the four extremities; and between the two lower, there is a curious prolongation like a tail, which has been called the coccygeal protuberance.

In an embryo of about seven weeks, the proportional size of the head is so much less, that the peculiar form of the human body is quite apparent. Two small pores are perceptible in the region of the nose; and the superior extremities seem divided into arm and fore-arm.

In an embryo of about eight weeks, a small pore may be discovered, by the microscope, in the region of each auricle; a shoulder, arm, fore-arm, and hand, with five small tubercles in the situation of the fingers, can be easily distinguished with the naked eye; and in the lower extremities, parts can be seen corresponding to the thigh, leg, and foot; but there is no appearance of toes.

In an embryo of about nine weeks, there is a projection in the region of the nose; part of the auricles is formed; the toes have appeared; the pudenda begin to be distinguished; and the coccygeal protuberance can no longer be seen.

After this, considerable changes take place in the external appearance of the fetus, in proportion as the development of the different parts advances; but it would be impossible to convey an idea of these without the aid of engravings. Hair generally begins to appear on the eye-brows, and in the regions of the hind-head and temples, about the end of the fifth month.

4. Soemmerring has accompanied these representations with some remarks, which are worth attending to. The younger the fetus, he finds, the larger is its head, compared to the other parts of the body; the smaller its face, in proportion to the other parts of the head; and the smaller its limbs, relatively to the trunk. During the first, second, and third months, he has remarked, that the upper extremities are larger than the lower; but that, about the fourth, they are equal; and that, towards the fifth, the lower have become larger than the upper.

5. He has also pointed out the following curious distinctions, in external form, between the male and the female fetus. The head of the male differs from that of the female, in being larger in proportion to the whole body, less rounded, flatter in the crown, and more prominent behind. In the male, the breast is considerably more prominent than the umbilical region, while in the female it is the reverse; and this is a distinction perceptible in the youngest fetuses.

The trunk of the body, between the upper parts of the loins, is arched in the male, but hollow in the female; and this, too, is a distinction very early observable. The upper extremities in the male are a little longer, in proportion to the trunk, than in the female; the arms are less cylindrical; the fore-arms fuller; the wrists broader; and the ends of the fingers less pointed. The circumference of the body, at the haimches, is less in the male than in the female; the thighs are more slender; the feet longer; the malleoli and heels more prominent; and the great toe exceeds the others much more in length.

Stature.

6. We believe the mean height of the male, at the period of maturity, to be about five feet eight inches English measure; and the following are the comparative average dimensions of particular parts of the body:

| Dimension | Inch | |-------------------------------------------------|------| | Total height of the body | 68.00| | From the tip of one middle-finger to the tip of the other, the upper extremities being extended laterally to a right angle with the trunk | 68.00| | From the crown of the head to the top of the pubes | 34.00| | From the crown of the head to the lower margin of the chin | 9.75 | | From the lower margin of the chin to the top of the breast | 3.85 | | From the top of the breast to the pit of the stomach | 6.08 | | From the pit of the stomach to the navel | 6.08 | | From the navel to the top of the pubes | 6.08 | | From the top of the prominence of the shoulder to the fold of the elbow | 12.06 |

ANIMAL.

Anatomy. From the fold of the elbow to the top of the hand 10.02 The hand, measured in the palm, from the lower fold of the wrist to the point of the middle-finger 7.75 From the top of the inside of the thigh to the inside of the joint of the knee 14.06 From the inside of the joint of the knee to the sole of the foot 18.05 The foot, measured on the sole, from the posterior margin of the heel to the point of the great toe 9.75

Of the Female.

7. The average height of the female seems to be about five feet five inches; and the length of the different regions proportionally less than in the male.

8. The length of an embryo of three or four weeks represented by Soemmerring, is only about one-eighth of an inch; one of eight weeks is about an inch; and one at the end of the fifth month about ten inches. According to Mr Burns, (Principles of Midwifery, p. 121), however, the fetus, in the fifth month, is only about six or seven inches in length.

The same intelligent author states the length of the fetus in the sixth month to be about eight or nine inches; in the seventh about twelve inches; and in the eighth about fifteen inches.

According to the observations of Roederer (Comment. Reg. Soc. Scien. Gotting. 1753), the length of the fetus at the period of birth is, on an average, about 20½ inches.

9. The only individual part of the fetus, of which it is important to ascertain the average dimensions at the period of birth, is the head. Now, the longest diameter of the head, at this period, is that from the crown to the chin; and this seems in general to measure about five inches. The breadth of the head, at the same time, from one parietal protuberance to the other, is usually about 3½ inches. In an exceedingly interesting paper in the Philosophical Transactions (Phil. Trans. 1786), Dr Clarke has stated, that he measured the heads of sixty male, and sixty female children, born at the full time; and that he found the circumference passing through the occipital protuberance, and the middle of the brow, to be, on an average, 19.8 inches; while the arch from ear to ear over the crown was 7.32 inches. One measured fifteen inches in circumference, and one 8½ inches from ear to ear; but none were under twelve inches in the one direction, or 6½ inches in the other.

10. There are some general remarks on the progressive growth of the fetus by Soemmerring, accompanying the engravings to which we have already referred, which present some singular results. According to him, the most rapid increase of the fetus takes place during the first weeks, after conception. He has observed, however, that the growth does not proceed in a uniform ratio; but that it is a little retarded during the second month; accelerated during the third; again somewhat retarded at the beginning of the fourth; from the middle of the fourth to the sixth again accelerated; and from this period till the end of the ninth month once more retarded.

11. It seems to be well established, that there is a difference in the average dimensions of the male and female, even in the fetal state. Roederer found the mean length of sixteen male children born at the full time to be 20½ inches; and of eight females only 20½; and Dr Clarke, in his measurement of the heads of sixty male, and sixty female children, born at the natural period, found that the circumference was, on an average, 14 inches in the males, and only 13½ inches in the females, and the arch from ear to ear over the crown 7½ inches in the males, and only 7½ in the females. Out of one hundred and twenty children, there were only six in whom the circumference of the head exceeded 14½ inches, and these six were males.

Weight.

12. We have examined a register of the weights of about fifty full grown males of the average stature, and find their mean weight to be about 140 lbs. English Troy. The average weight of an equal number of adult females, we suppose, would be found to be about 30 or 40 lbs. less; but we have had no opportunity of ascertaining this.

13. The average weight of the fetus in the earlier months is uncertain. According to Mr Burns (Principles of Midwifery, p. 121), however, it generally weighs about 2 oz. in the twelfth week; about 1 lbs. in the sixth month, and about 4 or 5 lbs. Troy in the eighth month.

14. Its mean weight at the natural period of birth has been better ascertained. It seems to be about 7 lbs. avoirdupois. The celebrated Dr Hunter (Anatomical Description of the Gravid Uterus, p. 68) states, that of several thousand new-born and perfect children, which were weighed at the British Hospital in London by Dr Macaulay, the smallest was about 4 lbs., and the largest about 11 lbs. 2 oz.; but by far the greatest number were from 5 to 8 lbs. avoirdupois. He adds, that he never knew an instance of a child born at the natural period that weighed 12 lbs. avoirdupois. Of sixty male and sixty female children, born at the full time, which were weighed by Dr Clarke, the lightest was 4 lbs., and the heaviest 10 lbs.; and the average weight was 7 lbs. 13 dr. avoirdupois. The average weight of twenty-six children, born at the natural period, which were weighed by Roederer, seems to have been about 6½ lbs.; the heaviest being 8 lbs., and the lightest about 5½ lbs.; but we are uncertain as to the scale of the weights which he employed.

15. Dr Clarke estimates the difference between the average weight of the male and female at birth at about 9 oz. avoirdupois; and the results of Roederer's observations do not appear to differ materially from this estimate.

16. In cases of twins, it would seem that the weight of each twin is in general less than the average weight of single children, though their combined weight is greater. Dr Clarke found the average weight of twelve twins to be 11 lbs. avoirdupois a pair; the heaviest pair weighing 13 lbs., and the lightest 8½ lbs. Mr Burns, however, states, that he has known instances, in which each twin was rather above than under the usual weight of a single child. PART II.

OF THE ANATOMY IN GENERAL OF THE COMMON SYSTEMS AND COMMON TEXTURES OF THE BODY.

17. By the common systems of the body, we mean the Circulating System, the Absorbent System, and the Nervous System; and by the common textures, Cellular Substance, Adipose Substance, Muscle, Skin, Hair, Cartilage, Bone, Tendon, Serous Membrane, and Synovial Membrane.

18. We have applied the term Common to these Systems and Textures, because they are common to many parts of the body.

A general view of their structure and distribution, forms a proper introduction to the anatomy of individual parts.

ARTICLE I.

OF THE ANATOMY IN GENERAL OF THE COMMON SYSTEMS.

I. OF THE CIRCULATING SYSTEM.

This system consists of two parts; viz. the Heart and the Blood-vessels.

1. Of the Heart.

A. The Heart of the Adult Male.

19. When the cavity of the right auricle of the heart is laid open, we observe, on the lower part of its posterior surface, an elliptical, but very superficial depression, which slopes a little backwards, and is called the oval fossa. This fossa is about half an inch long, and the third of an inch broad, with smooth edges, and having its long diameter turned upwards and downwards. Its size, however, varies very much in different individuals, and frequently it is entirely wanting.

Several Continental anatomists have lately affirmed, that there is, in general, a small slit, sufficient to admit the point of a probe, immediately behind the upper margin of this fossa, which inclines upwards, and a little to the left, and opens into the left auricle. We have seen this passage only in a few instances; but the authorities are so respectable, by whom it has been said to occur in a majority of cases, that we cannot doubt the statement to be correct.

20. The Eustachian Valve has not hitherto been described with sufficient accuracy. This is a thin, whitish, crescentic fold, situated immediately to the left of the opening of the inferior vena cava into the right auricle. Its posterior horn is connected with the left edge of the oval fossa, and its anterior with the right surface of the auricle, directly above the opening of the lower cava; so that it runs from behind obliquely forwards, and to the right. Its free curved edge looks upwards, and a little backwards; and one surface of it is continuous with the left and anterior side of the inferior cava, while the other is turned towards the left and fore part of the auricle. Were it prolonged straight upwards, it would run into the upper margin of the oval fossa; and, even as it is, when we look into the auricle from before, it cuts off from our view the lower half of this fossa. Its breadth and thickness vary extremely. Sometimes it is nearly half an inch broad, at other times scarcely perceptible; in some it is as thick as a wafer at its attachment, but tapering towards its edge, and without any holes in it; in others, it is as thin as silk-paper, transparent, and quite reticulated.

21. In the heart, as we usually find it after death, Capacity of the cavities of the ventricles always appear larger than those of the auricles. In general, also, the cavities of the right side appear to be more capacious than those of the left; the difference between them, however, being less in some cases than in others. In some instances they seem pretty nearly alike.

22. A variety of experiments have been made, with a view to ascertain precisely the capacities of these cavities after death; * but none of them can be regarded as quite satisfactory. In some, it is uncertain, whether precautions were taken to prevent the fluid employed in the measurement, from escaping by some of the blood-vessels communicating with the cavities. In others, it is doubtful whether certain coagula of blood, which generally form in these cavities after death, had been carefully removed; and in others, again, allowance is not said to have been made, for the extension of the cavities, which the weight of the fluid employed would necessarily produce.

In several experiments, in which we endeavoured to guard as much as possible against these sources of fallacy, we found, that the right ventricle of an adult heart contained two and a half ounces of water, while the left had only two ounces. Still, however, we are not disposed to place much reliance upon these, or any experiments of the kind.

23. The whole external surface of the heart is covered with serous membrane, which is thickest and strongest in the auricles.

Under this, at particular parts, is a quantity of adipose substance, which, shining through the serous membrane, gives the heart a straw colour at those parts.

Under both these is situated what is called the muscular coat; and within this, and lining the whole inner surface of the heart, is found the inner membrane.

24. This inner membrane in the cavities of the ventricles is as thin as silk-paper, perfectly transparent, and without the slightest appearance of fibres. Neither blood-vessels, absorbents, nor nerves, have yet been seen in it. Maceration in water renders it slightly opaque. It is easily detached from the muscular fibres which it lines, but no intermediate cellular substance can be seen between them. It is too tender to admit of being peeled off in large patches.

In the right auricle, the inner membrane lining the fleshy cords is quite similar to that in the ventricles; but in all other parts of this auricle, and over

* See Senac, Traité, &c. I. p. 189. Haller, Elem. Physiol. I. p. 323-7. Le Gallois, Diction. des Scien. Med. V. p. 434. the whole of the left also, it has a different appearance. It is whiter, and considerably thicker and stronger, than serous membrane. After slight maceration, it is disposed to peel in laminae; but no fibres are perceptible in it, and, so far as we know, no one has yet seen in it, either vessels or nerves. It is firmly connected to the muscular coat by a fine cellular substance.

The Eustachian valve, and the valve of the coronary vein, appear to be formed of doublings of the inner membrane of the auricle. The former, however, generally contains a fasciculus of muscular fibres at its basis, which is included between the folds of the membrane.

25. The structure of the tricuspid and mitral valves is not so simple. A delicate prolongation of the inner membrane of the auricles can indeed be traced over their inner surface; but we have never been able to detect any similar continuation of the membrane of the ventricles over their outer surface. They seem to consist of a fine but dense web of slender fibres continued from the tendinous cords. These cords, as their name imports, are composed of tendinous substance; and, after they have been inserted into the valves, they spread out and are interwoven in every direction, as may be easily seen by holding the valves between the eye and the light. It is the intersections of these cords, just after their insertion, that causes those knots and ridges which are so common on the valves, particularly on the mitral valve.

B. The Heart before Maturity.

26. There is a considerable difference, in point of shape, between the heart of a fetus and that of an adult, resulting from the greater proportional size of the tips of the auricles in the latter. In a fetus of three or four months, these are so large, that they almost come into contact over the anterior part of the root of the pulmonary artery. As the fetus grows older, however, they gradually diminish proportionally; so that after birth there is scarcely any peculiarity in this respect.

27. The most striking and important peculiarity of the fetal heart is the oval hole in the septum, between the auricles. This occupies exactly the situation of the oval fossa in the adult heart. The communication, however, between the auricles through it, is not direct. For, if we examine the heart of a fetus about the fourth month, we shall find, that there is a thin pellucid membrane laid over the oval hole, like a valve, on the side next the left auricle. The insertion of this valve below, is into the very edge of the lower third of the oval hole itself; but above this, its attachment is into the surface of the septum next the left auricle; extending farther and farther out from the margin of the hole as it ascends. When it gets on a level with the upper border of the hole, it begins to incline inwards again; and, after running a short way, stops; leaving a free curved edge, turned upwards, and a little to the left.

As this valve, then, is longer than the oval hole, it is obvious that, if it were stretched tight across it, like the parchment of a drum, it would prevent all communication between the auricles. But it is twice as broad as the space included within the line of its insertion, so that it admits of being pushed a considerable way towards the cavity of the left auricle. When this is done, a short canal is formed, between the upper part of the valve and the portion of the septum immediately above the oval hole, opening into the left auricle by an orifice, of which the floating edge of the valve forms fully two-thirds. The axis of this canal corresponds exactly with the axis of the inferior vena cava.

Whether there be any period prior to the fourth month, at which the oval hole has no valve, or at which it is smaller, we have not had satisfactory means of ascertaining. But Haller (Elem. Physiol. VIII. Pars I. p. 375.) mentions, that his friend Bergen had found none in a fetus of two months; and Senac (Traité, &c. Vol. I. p. 231.) believes that there is none prior to this at least, and expresses himself certain, that if its rudiments exist at two months, they are extremely small. After this period, according to him, it grows by degrees, and its margin approaches nearer and nearer to the upper border of the hole.

It is very probable that this description is correct; but, as we have found that the valve, even in the fourth month, is very easily broken, unless the heart be dissected with great care, nothing but actual observation will satisfy us on this point.

The hole and the valve remain pretty nearly in the state we have described, until about the commencement of the ninth month; when a considerable change begins to take place. The valve becomes thicker and tighter, and its free margin narrower; consequently the passage between the auricles becomes smaller. The sides of the hole itself are at same time thickened. The valve at last becomes so much tighter, and its upper border so much narrower, that the parts assume the appearance of the oval fossa, with a small slit at top, as already described. How long this process is of being completed, we have not ascertained; but we suspect, from an examination of several hearts, that it is not until two or three months after birth at least.

28. The Eustachian valve in the fetal heart is subject to as much variety, in point of size, almost as in the adult.

29. The auricles of the fetal heart are obviously larger, in proportion to the ventricles, than those of the adult; but the relative capacities of the right and left cavities, at this early period, have not been ascertained. They have generally appeared to us to be pretty nearly the same; or, if there was any difference between them, the left auricle and ventricle seemed rather the larger. Le Gallois has lately made some experiments on this subject (Diction. des Sciene. Médic. V. p. 440.); but they can hardly be regarded as satisfactory.

2. Of the Blood-Vessels in general.

A. Of the Arteries in general.

30. The arterial system of the human body resembles the trunks and branches of two trees. One trunk, called the pulmonary artery, arises from the right ventricle of the heart; and the other, denomi- Anatomy, Animal.

31. After the arteries have ramified to a certain degree of minuteness, they become so thin and transparent, that it is impossible to follow them, either with the naked eye, or with the microscope. In order, therefore, to render these very small vessels visible, anatomists inject into them thin coloured fluids, such as a weak solution of glue mixed with vermilion; and all our knowledge of the ultimate ramifications of arteries is derived from these injections.

32. Some arteries are seen distinctly terminating in veins; others vanish from our sight; but in what manner they end is uncertain. The termination in veins, therefore, is the only one capable of demonstration; every other matter of opinion.

33. All arteries, which are not less than the twelfth of an inch, may easily be shewn to be composed of three coats, an inner, middle, and outer.

34. The inner coat resembles exactly the inner membrane of the ventricles of the heart. It is equally thin, and perfectly transparent and colourless; and its inner surface is smooth. No vessels or nerves have yet been seen in it. It may be peeled off from the middle coat with the forceps; but it is too tender to separate in large patches. It differs from the inner membrane of the ventricles of the heart, in being a good deal more elastic.

35. The middle coat of an artery is the thickest; being about twice the thickness of the outer one. It consists of slender fibres laid closely together, side by side, without any apparent connecting medium, and placed uniformly in a circular direction, surrounding the artery, and in a plane perpendicular to its axis. Those which are more internally situated, may be easily seen through the transparent inner coat, when the artery is slit open; and if this coat be peeled off, the fibres of the middle one may be easily raised with the forceps in successive strips, all of which separate in a transverse or circular direction, exactly like the outer bark of a birch tree.

In the larger arteries, the fibres are of a yellowish or straw colour, and firm in their consistence; but, in the smaller vessels, they are softer and more flesh-coloured.

36. The outer coat of arteries differs extremely from the other two. It consists of slender, white, shining fibres, very dense and tough, closely compacted together, and interwoven in every direction. It is very difficult to separate them from each other, and impossible to make them peel in any regular manner.

37. Many arteries are surrounded with cellular substance externally; but this is merely an accidental covering. It is not a necessary part of the arterial tube; and cannot, therefore, with propriety be described as one of the coats of an artery.

38. In arteries which are less than the twelfth of an inch, it is not easy to distinguish the different parts which compose them. But there is every reason to believe that they have the same structure as the larger vessels.

B. Of the Veins in general.

39. The distribution of the veins throughout the body, like that of the arteries, resembles the ramification of a tree; but, in describing them, it is usual to invert the order observed in tracing the arteries, and to consider the trunks as successively formed by the union of the branches.

40. When we apply the microscope to a thin or transparent part of the body, which has been properly injected, we can perceive many of the most minute veins, arising from the extremities of equally minute arteries, and distinctly continuous with these. Any other origin of veins than this is quite uncertain.

41. Many of the larger veins, and veins of middle size, are provided with valves. These are membranes of a semilunar shape, perfectly transparent and colourless, and though scarcely the thickness of a hair, yet very dense and strong. They are attached by the whole of their curved margin to the inner surface of the vein; and this margin is uniformly turned towards the branches of the vein, while their free straight edge looks towards the trunks. They are inserted into the sides of the vein in such a manner, as to be in a certain degree loose within the tube; and, accordingly, when any fluid is forced from the trunks towards the branches, they are pushed inwards from the sides of the vessel towards its axis. They vary very much in their dimensions, even in vessels of the same calibre. Sometimes they occur single, particularly in the smaller vessels; sometimes, though very rarely, three are found together; but, in general, they are disposed in pairs, one exactly opposite to the other. They are very seldom so large, or so precisely adapted to each other, as to shut up the tube of the vessel completely. The number of them occurring either singly or in pairs, within any given extent, is very various in different veins. They are found at intervals of from four or five inches to a quarter of an inch, or even less. In general, they are most numerous in veins of small size.

In all veins that are not less than a twelfth of an inch in diameter, two coats can be distinctly demonstrated; and in some, portions of a third texture intervene between these two.

42. The inner coat of veins is transparent like that of arteries. It is a little thicker, however, and coat greatly stronger; and it differs also from the inner coat of arteries in this, that it can be distinctly separated into slender dense fibres.

43. The outer coat of veins has the same structure as the outer coat of arteries. It is thinner, however, proportionally, and its fibres are not so close.

44. In almost all the trunks and larger branches of veins, a substance is found intervening between these two coats; sometimes surrounding the vein entirely, but in general occurring in patches of different sizes. It varies a good deal in its thickness; being as thick in some parts as the outer coat, and only II. OF THE ABSORBENT SYSTEM.

45. The Absorbent System of the human body consists of Absorbent Vessels and Absorbent Glands.

1. Of the Absorbent Vessels in general.

46. The absorbent vessels are a system of tubes, distributed throughout the body in the manner of the blood-vessels. They are described in the same manner as the veins. Exceedingly minute at first, they unite one with another, and at last form two trunks, each about a quarter of an inch in diameter, which open into two veins called subclavio-jugular veins, one on each side of the neck; the left trunk being denominated the thoracic duct.

47. There is no part of the body, in which the absorbent vessels can be traced to their beginnings with the naked eye. Cruikshank was fortunate enough, in one case, to find the absorbents of the alimentary canal so turgid with a milky substance after death, that, with the microscope, he could distinctly trace hundreds of them to their origins, which had the appearance of circular orifices. (Anat. of Absorb. Vessels, p. 56.) But this is the only part of the body, in which the commencements of these vessels have been seen, even with the microscope.

48. Little is known respecting the structure of the absorbent vessels; they are too delicate to admit of satisfactory dissection. We have examined, however, pretty minutely, the thoracic duct; and it seems to us to consist of one coat only. This resembles the inner coat of veins; and the valves of the absorbents appear to be merely prolongations of it.

2. Of the Absorbent Glands in general.

49. These bodies may be regarded as consisting of a peculiar substance enclosed in a capsule.

50. We are inclined to regard Mascagni's description of the structure of the former, as by far the most accurate which we yet possess. (Vas. Lymph. Hist. p. 30.)

51. According to this very respectable authority, the vasa inferentia, before entering a gland, divide into branches. Some of these penetrate directly into the central parts of its substance, while others are distributed towards the surface. The larger branches are bent, convoluted, and interwoven, in every direction; they communicate freely with each other; and become suddenly narrow in some parts, while they swell out into little cells at others; so that when the gland is injected with quicksilver, its whole outer surface seems as if covered with little rounded eminences. The smaller branches subdivide, and form a net-work on the surface, and then either dip down between the cells of the larger ones, or open into them. Various small vessels, on the other hand, are seen, either arising from these cells, or ascending from between them, and after winding about, uniting together into larger branches, which at last constitute the vasa efferentia.

Sometimes the absorbent vessels of a gland present a pretty uniform diameter throughout; so that there is little or no appearance of cells in any part of it.

52. The capsule of absorbent glands is a thin, transparent, and colourless membrane, very vascular, suctile, and resolvable by maceration into fine whitish fibres.

III. OF THE NERVOUS SYSTEM.

53. The Nervous System may be divided into two parts; the Central Mass, and the Nerves.

1. Of the Central Mass.

54. The central mass of the Nervous System is composed of the Brain and the Spinal Cord. We shall offer a few remarks on each of these separately.

A. Of the Brain.

a. The Brain of the Adult Male.

55. The brain weighs, in general, about 2½ lbs. or 3 lbs. avoirdupois. Both its weight, however, and its volume, vary a little in different individuals; but without any fixed relation to the weight or stature of the individual.

56. It is almost symmetrical; its median plane corresponding to the median plane of the whole body; so that it is divisible into two halves, right and left, very nearly alike.

57. It is usually regarded as consisting of two parts; an upper part, denominated the Brain Proper, and a lower one, called the Cerebellum.

58. The brain proper weighs in general from 3½ to 4½ oz. and the cerebellum from 5 to 8 oz. avoirdupois.

59. The brain is composed almost entirely of a peculiar substance, which we shall call nervous matter, embraced by delicate membranes.

b. The Nervous Matter of the Brain.

60. There are two kinds of this matter; the one usually denominated medullary, and the other cinerious. We prefer, however, to distinguish them by the terms white and brown.

61. The white nervous matter is of different shades, in different parts of the brain. In most parts, its colour resembles a mixture of orange-white, and wine-yellow (see Syme's Nomenclature of Colours); and this kind we shall call orange-white. In others, it approaches more nearly to the wine-yellow; and this species may be denominated yellowish-white.

62. The consistence of the white nervous matter varies a little in different parts. In general, it is less elastic than jelly, but somewhat more glutinous or viscid.

63. When we make a section of it in any direction, with a sharp scalpel, it appears perfectly smooth, and of a uniform colour. A few reddish points and striæ divided may be observed here and there; but there is no appearance whatever of cells, or globules, or fibres.

64. It has been subjected to very minute microscopic examination by Prochaska. (Oper. Min. Pars. p. 342.) When he took a small portion of it, either from the brain proper, or the cerebellum, and spread it on a thin plate of glass, so that it became pellucid, and then examined it with a powerful microscope, he found that it resembled a sort of pulp, consisting of innumerable globules, or particles of a roundish form. A little water added to this pulp, divided it into a number of flocculi; but he observed that each flocculus was still composed of a number of globules. He very rarely found one globule by itself, or even two, floating in water, apart from the rest. Maceration in water, even for three months, was insufficient to separate them from each other. He concluded, therefore, that they were united by means of a very delicate and pellucid cellular substance. The globules, he observed, were not all of the same size; but varied a little in dimension, even in the same part of the brain. In general, however, he found them, both in the brain proper and in the cerebellum, to be more than eight times smaller than a globule of the blood. The most powerful microscopes did not enable him to discover anything satisfactory respecting their structure.

65. These observations have, within these few years, been prosecuted, on a much more extensive scale, by Joseph and Charles Wenzel. (De Pe- ciliis. Struct. Cereb. p. 24.) They have uniformly found that the white nervous matter seemed as if entirely composed of extremely small globules, or corpuscles of a roundish form, putting on the appearance of little cells, filled with proper medullary substance.

No estimate is given of the dimensions of the globules; but they describe them as being exceedingly minute, and as being all pretty nearly of the same size. They seemed to adhere very closely to each other, without any apparent connecting medium. The globular appearance continued distinctly perceptible, in portions of the substance, which had been long exposed to the action of rectified spirit of wine and muriatic acid; nor was it even destroyed by steeping the matter in alcohol, and then drying it.

66. White nervous matter possesses considerable vascularity. The arterial branches, however, which supply it, are seldom much larger in diameter than a common pin; and the veins are for the most part equally small. It is the division of blood-vessels which produces the appearance of red points and red striæ in this matter, when incisions are made through it.

67. When a portion of white nervous matter has been immersed in boiling oil for a few minutes, or steeped for a few days in alcohol, or diluted muriatic or nitric acids, or a mixture of alcohol and acids, or a solution of corrosive sublimate, its consistence is greatly increased; and if we tear it into fragments, we find that the surfaces of the fragments exhibit a fibrous appearance. White threads, as slender as a hair, may be raised from these surfaces with the point of a pin; and the whole substance seems to be formed of such fibrils placed close to each other. The delicacy of these threads, and the closeness with which they are compacted together, render it quite impossible to ascertain their actual length, or even to form a conjecture as to the extent to which they may be subdivided.

Whether the white nervous matter in all parts of the brain be susceptible of this change on coagulation, does not seem to us satisfactorily established.

68. In the chemical analyses which have hitherto been made of the nervous matter, the white species does not seem to have been distinguished from the brown. This circumstance deserves to be attended to, in reading the fullest analysis of the nervous matter which has yet been made, viz. that by Vauquelin. (Annal. de Chim. Tom. LXXXI.)

69. The brown nervous matter varies a little in its hue also. Its most common colour is wood-brown; but sometimes it is like a mixture of wood-brown and lead-grey; and this last colour we may call greyish-brown.

70. It is softer than white nervous matter, and in many parts is more vascular. It exhibits the same appearances, however, when divided with the scalpel; and seems to be composed of similar globules when examined with the microscope. In certain parts, too, of the brain, we have found, that when congealed by boiling oil, or acids, &c. it appears fibrous on laceration; but whether or not the brown matter generally be susceptible of this change, we have not ascertained.

71. These two kinds of nervous matter, the white and the brown, are intermingled within the brain in various ways. In some parts, a covering of the one surrounds a mass of the other, as a capsule encloses a nucleus; in others, they are alternated in laminae or strata; and in others, they traverse each other in the form of cords or fibres of various sizes. Yet, notwithstanding this diversity in their arrangement in different parts, their disposition in each particular part is observed to be remarkably uniform.

72. The only attempt, worthy of notice, which has yet been made to represent the proportions and arrangement of those two kinds of matter in the brain, in a series of coloured engravings, is that by Vieq d'Azyr, in his folio work, entitled Traité d'Anatomie et de Physiologie, published at Paris in 1786. The chief merit of this work, however, consists, not in the engravings themselves, which are seldom entitled to the praise of accuracy, either in point of form or colouring, but in the minute explanations and details which accompany them.

73. There are peculiarities in the structure of the pituitary gland and pineal gland, which deserve to be further investigated.

The pituitary gland is a good deal firmer than the other parts of the brain, and seems to be intersected by a texture different from common nervous matter. When it is pressed between the fingers, the nervous matter appears as if it were forced out of a sponge. In general, two distinct masses may be perceived in it; one occupying the fore part, approaching rather to purple in its colour; and another behind, softer in its consistence, and of a lighter hue.

74. The pineal gland also contains two substances very different from each other. One is a matter somewhat like brown nervous matter, but softer than that matter generally is; and the great bulk of the gland is made up of this substance. The other is like grains of sand, consisting of hard, semitransparent, yellowish particles, varying a little in size, but seldom larger than the head of a pin. Sometimes these particles are grouped together into a heap or acervulus on the upper surface of the gland, close to its base; at other times they form a sort of chain... Anatomy, or ridge along its margin; and at other times again Human, they are irregularly scattered through its substance. There is the greatest variety in their number. In two or three instances, after the strictest search, we have not been able to find more than a single particle within the whole gland. We have made a few chemical experiments on these particles, and are rather inclined to think that they have the same composition as bone.

b. The Membranes of the Brain.

75. The membranes of the brain are two in number, the Pia Mater and the Arachnoid Membrane.

* The Pia Mater.

76. All the arterial vessels which enter into the composition of this membrane, seem destined ultimately to supply the nervous matter of the brain; and this matter appears to derive arterial vessels from no other source. The same remark applies to the veins of the pia mater; so that we may regard this membrane as a vascular covering formed of blood-vessels, which are just about to penetrate the nervous matter of the brain; and of blood-vessels which have just emerged from it.

77. After a minute injection, it is difficult to perceive anything in the pia mater but blood-vessels; and these are interwoven in every direction. We have not yet been able to discover any absorbents or nerves in it. There is an appearance of very fine dense white threads in it, at particular parts, where it happens to be but loosely connected to the arachnoid membrane; but it is uncertain whether these are not blood-vessels. We cannot perceive any cellular tissue in it, such as Bichat has described, Anat. Descrip. III. p. 27.

** The Arachnoid Membrane.

78. This differs very much from the former, both in structure and distribution.

It is as thin as a cobweb, dense, colourless, and almost perfectly transparent. Its outer surface is quite smooth; its inner, more or less thready or flocculent, according to its connection with the pia mater.

Nothing is known respecting its structure. We have never seen blood-vessels in it, either in its healthy or diseased states; with or without previous injection. It has hitherto proved equally impracticable to demonstrate in it either absorbents or nerves. Bichat classes it with the serous membranes (Anat. Descrip. III. p. 32.) but it is so little analogous to these in point of structure, that we prefer to regard it as a peculiar membrane.

b. The Brain of the Adult Female.

79. It has been often affirmed that the brain of the female differs from that of the male, slightly, both in form and dimensions. We cannot say, however, that we are satisfied of the truth of this observation. The point requires to be further investigated.

c. The Brain before and after Maturity.

80. On this subject, hardly anything satisfactory was known, until within these few years.

81. We have already had occasion to refer to a work by the Wenzels, entitled De Penitiori Structura Creberi Hominis et Brutorum, which was published, in folio, at Tubingen, in 1812. We strongly recommend this treatise to the attention of our readers. It appears to us the best and most original work on the structure of the brain, which has appeared for more than a century. The authors seem to have employed themselves, unremittingly, in investigations relating to the anatomy of this organ, for upwards of twelve years, and in circumstances singularly favourable for observation. There is little of importance relative to the state of the brain at different periods of life, at present known, for which we are not indebted to their labour and ingenuity.

82. From a variety of facts, which our limits will not permit us to give in detail, we select the following respecting the dimensions and weight of the brain, which seem to be the results of an immense number of observations.

83. First, with respect to dimensions, they find its Dimensions that both the brain proper and the cerebellum increase rather more in length and in breadth, during the six months immediately preceding birth, than during the first seven years after birth; that these dimensions arrive at their maximum at the age of seven; and that they suffer no change during the whole of after-life.

84. Secondly, with regard to weight, they ascertained, that the weight of the whole brain, most commonly arrives at its maximum, at the age of three years, and remains without diminution, during the whole of after-life; the maximum being in general from 20,000 to 22,000 grains, and seldom exceeding 24,000. The weight of the brain proper, at the age of three years, they found, does not exceed, in general, 21,000 grains; nor that of the cerebellum 2000 grains. The younger the fetus, they observed, the greater was the ratio of the weight of the brain proper to that of the cerebellum. This ratio, it appeared, was usually about seven to one, at the age of three years, and remained so ever after.

B. Of the Spinal Cord.

a. The Spinal Cord of the Adult Male.

85. We regard the spinal cord as beginning at the lower margin of the annular protuberance of the cerebellum. The arrangement which includes a portion of its upper extremity, along with the brain, under the name of medulla oblongata, seems to us neither so precise nor so natural.

86. From a few actual measurements of it, we are inclined to think, that its length, in general, is about thirty inches. Chausser says, its weight is from about a nineteenth to a twenty-fifth of that of the whole brain. (Exposit. Sommaire, p. 119.)

87. Like the brain, it consists of nervous matter, enclosed in membranes.

a. The Nervous Matter.

88. This differs very little, apparently, from that of the brain. The cord contains both kinds of it.

89. The white matter is chiefly of the orange-white species, and is firmer than the same kind of substance in any part of the brain, except the annular protu- The brown matter is chiefly of the greyish species.

90. The nervous matter does not extend the whole length of the cord; it ceases within nine inches of its extremity, and the membranes alone form the rest.

91. It may be divided into three portions. The first portion may be called the top of the cord or cranial portion, and is about an inch in length. This is what is denominated by many the medulla oblongata. The second is about five inches in length, and may be denominated the cervical portion; and the third, which is about fifteen inches long, we shall call the dorsal portion.

92. The arrangement of the two kinds of nervous matter in the cord, has not hitherto been described or represented with sufficient accuracy. The whole of the cervical and dorsal portions, and the lower part of the top of the cord, consist of a central column of greyish-brown matter, surrounded by a stratum of orange-white. The upper half of the top, contains a much larger proportion of white nervous matter, than any other part of the cord.

93. We have found that considerable portions of the nervous matter of the cord, are rendered fibrous in the longitudinal direction by coagulation.

b. The Membranes.

94. The Membranes of the spinal cord are three in number; the Pia Mater, the Serrated Membrane or Ligamentum Dentatum, and the Arachnoid Membrane.

It will be necessary only, on the present occasion, to say a few words with respect to the second of these.

95. The serrated membrane is whitish and semi-transparent in its appearance, and thinner than the pia mater, yet fully stronger. Its inner border, which is straight, is intimately connected with the pia mater; while its outer one presents a series of angular projections or teeth, each of which is attached firmly to the dura mater of the spinal canal.

96. In its internal structure, it most resembles the substance called tendon.

97. It begins at the top of the cervical portion of the cord, and ends, in general, just where the swelling commences on the lower part of the dorsal portion. After it has terminated, a very slight ridge may be seen running down from it, on the surface of the pia mater, and exactly in the same direction, for about an inch and a half. We have never seen it, however, reach the extremity of the cord.

b. The Spinal Cord of the Adult Female.

98. We are not acquainted with any material circumstances in which the spinal cord of the female differs from that of the male; but, according to Chausser (Exposit. Som. p. 117.), its nervous matter is softer.

c. The Spinal Cord before and after Maturity.

99. The nervous matter of the cord has been said to be proportionally shorter in the child than in the adult; but this has not been established.

100. Chaussier concludes, from a great many observations, that this matter is firmer at birth than at any other period of life, and that it gradually becomes softer as the individual advances in years. We suspect some fallacy in this remark.

101. We are inclined to think, that the central column of brown nervous matter in the cord, is larger proportionally, and darker in its colour, at birth, than at any after period of life. We have often observed, in old persons, that it had entirely disappeared; its place being occupied by white matter; and we find that Chaussier states this to be a constant occurrence in the decline of life. (Exposit. Som. p. 146.)

2. Of the Nerves.

102. The nerves are cords of a peculiar structure, connected either directly, or indirectly, with the central mass.

103. There is the utmost variety in the mode of their distribution. Many of them may be seen spreading themselves out by regular ramification. Others divide into branches, and then soon after unite into trunks again. Others may be traced into a net-work or plexus, formed of various nerves interwoven in every direction, but in which each individual nerve is in a manner lost; and which sends off new branches to be expended by new ramification, or to unite with new plexuses. There is but one nerve in the body which neither exhibits ramification, nor is connected with any other nerve by plexus throughout the whole of its course. This is the optic nerve.

104. At the union of two or more nervous branches Ganglia, with each other, certain knots or tumours frequently present themselves, which have been called ganglia; and the same name has been extended to similar swellings, which very often occur on single nerves. These ganglia are of various shapes and sizes; none of them exceeding three quarters of an inch, or an inch.

105. Many nerves are attached directly to the central mass; and in such cases, the extremity of the nerve which happens to be connected to the Primary brain or spinal cord, is invariably considered as its origin. We propose to denominate all those nerves which have such an origin, primary nerves. Those which take their origin in plexuses, or ganglia, or in other nerves of which they constitute branches, we may call secondary nerves.

106. The primary nerves communicate, more or less intimately, with all the secondary nerves, by means either of ramification, or plexus, or ganglion. Hence, all the nerves in the body are said to be connected, either directly or indirectly, with the central mass of the nervous system.

107. Nerves are composed of filaments of nervous matter enclosed in sheaths of a peculiar substance, hence called neurilema. The structure and arrangement of these were first well described by the late Professor Reil. (Exercitat. Anatomi. Fascic. Prim.)

108. The filaments of nervous matter are of different sizes in different nerves, and sometimes even in the same nerve. They seldom, however, exceed the thickness of a hair; and in most instances, are smaller than the finest fibre of silk or cotton, so that it requires a microscope to see them distinctly. They are placed side by side; and in their course, divide, and subdivide, and reunite, and run into each other, forming the most intimate connection. The greater number of the nerves in the body, consist of several separate fasciculi of these filaments; some of only one fasciculus.

109. The neurilema, or substance which surrounds each filament, and ties the filaments into fasciculi, &c., is, in most instances, so like cellular substance, that we may regard it as a species of that texture.

110. Scarpa's description and representations of the structure of the ganglia, are by far the most accurate which we yet possess. (Anatom. Annotat. Lib. Prim.) There is a good deal, however, connected with this subject which requires to be farther investigated.

111. In these bodies, the fasciculi of nervous filaments attached to them, suffer a temporary subdivision and separation from each other, and are then combined anew. The intermixture of fasciculi which takes place within them, is in general so intimate, that it looks as if every fasciculus of every nerve, which emerges from a ganglion, contained more or fewer filaments from every fasciculus of every nerve which entered it.

112. Each fasciculus, in its progress through a ganglion, seems to be provided with its proper neurilema. But, besides this, the spaces left between the intersections of the fasciculi, are filled up with a peculiar soft substance, of a greyish, sometimes a yellowish, colour. This substance does not seem to us to have the slightest resemblance to the brown nervous matter of the brain and spinal cord; although it has been very confidently pronounced to be the same by some anatomists. Scarpa regards it as a peculiar cellular substance, filled with a mucilaginous or oily matter.

113. There are eighty-four primary nerves in all; forming forty-two pairs. The nerves of each pair arise, one from each half of the central mass, at corresponding points.

114. Some of these arise from the brain, others from the spinal cord; they may, therefore, be divided into cerebral and spinal.

115. There are eight pairs of cerebral nerves. These are the following:

- The Olfactory nerves. - The Optic nerves. - The Common Oculo-muscular nerves. - The Internal Oculo-muscular nerves. - The External Oculo-muscular nerves. - The Trigeminal nerves. - The Facial nerves. - The Auditory nerves.

116. There are thirty-four pairs of spinal nerves; and, these are:

- The Glosso-pharyngeal nerves. - The Pneumo-gastric nerves. - The Hypo-glossal nerves.

The Accessory nerves. The Sub-occipital nerves. The Cervical nerves, Seven pairs. The Dorsal nerves, Twelve pairs. The Lumbar nerves, Five pairs. The Sacral nerves, Five pairs.

117. We have purposely avoided applying any numerical appellations to the primary nerves, which arise from the brain, and the top of the spinal cord; in order that there might be the less risk of their being mistaken by those who have long been accustomed to the old, but very inaccurate, numerical nomenclature.

**Article II.**

**OF THE ANATOMY IN GENERAL OF THE COMMON TEXTURES.**

I. **THE ANATOMY IN GENERAL OF CELLULAR SUBSTANCE.**

118. From the term cellular, which has long been applied to this texture, one would naturally be led to suppose, that it was a substance formed into cells, admitting of easy demonstration. But this is far from being the case. In a mass of it, examined with the microscope, we can perceive nothing but exceedingly delicate fibres, interwoven in every direction. It is only when it is distended, or when we endeavour to tear its parts asunder, that it exhibits a cellular appearance.

119. If we lay hold of a mass of it between the fingers, and pull it gently, it immediately separates itself into innumerable transparent laminae, finer than the finest cobweb, which intersect each other in every direction, and leave spaces or cells between them of various shapes. The same effect may be produced, by inserting the point of a blow-pipe into the midst of the substance, and blowing into it; or by an injection of water, or any thin fluid. In proportion as we pull or distend the substance, the smaller laminae successively give way, and several cells are thus united into one; until at last the whole are torn. The instant the distention is discontinued, the parts collapse, and the cellular appearance vanishes.

120. It remains, therefore, to be determined, whether this substance consists, in its natural, undistended state, of numberless fine laminae, of a definite size and form, closely applied to each other; or whether the cells which it exhibits, when distended, be not merely the effect of the accidental separation of layers of the substance, always accompanied with greater or less laceration of parts, and of course varying with the direction and degree of the distending force.

---

* Synonym. Lat. Motores communes oculorum. † Synonyms. The fourth pair, according to the old enumeration. Lat. Nervi pathetici. ‡ Synonym. Lat. Abductores oculorum. § Synonyms. The fifth pair, according to the old enumeration. Fr. Les nerfs trifaciaux. || Synonym. The portio dura of the seventh pair, according to the old enumeration.

Synonym. The portio mollis of the seventh pair. ** Synonyms. The eighth pair of cerebral nerves, according to the old enumeration. Lat. Par vagum; nervi vagi. Fr. Les nerfs vocaux. †† Synonym. Fr. Les nerfs linguaux. ‡‡ Synonyms. Fr. Les nerfs spinaux; les nerfs spinocranio-trapeziens. Bichat has devoted a long chapter of his Anatomie Générale to the description of this texture. (Tom. I. p. 11.) It contains a great deal of matter, however, which is quite foreign to the subject; and, in other respects, is often vague and incorrect.

The most original remarks on this substance are to be found, in a paper by the celebrated Dr William Hunter, in the second volume of the Medical Observations and Inquiries.

II. THE ANATOMY IN GENERAL OF ADIPOSE SUBSTANCE.

122. This texture is obviously composed of two distinct substances; an oily matter, and a vascular texture formed into cells, in which this matter is contained.

123. The oily matter possesses all the characters of the fixed oils. It seems to us most probable, that it exists in the living body in a fluid state. We are led to entertain this opinion chiefly from some experiments, in which we raised portions of the adipose texture taken from the dead body, to the temperature of the living. But we have further observed, in surgical operations, that, when a thick portion of adipose substance happens to be divided, minute globules of oil may be seen swimming, in great abundance, in the stream of blood that flows from the wound.

124. The vascular texture which contains the oily matter, appears to be composed of a substance fully more delicate than cellular substance, and to consist of little spherical cells placed closely together side by side. These cannot be distinctly seen without a magnifying-glass. They vary a little in their size, but are all exceedingly minute. According to Dr Monro, none of them exceed the eight-hundredth part of an inch, nor are less than the six-hundredth. (Descrip. of the Bursae Mucosae.)

The cells of adipose substance have no resemblance whatever to the cells formerly described in cellular substance.

III. THE ANATOMY IN GENERAL OF MUSCLE.

125. Muscle seems to be composed of delicate fibres of a peculiar nature, surrounded and united together by a substance like cellular substance; and supplied with blood-vessels, absorbents, and nerves.

126. Prochaska's description of the fibres is still not only the most accurate, but the clearest which we possess. (See Oper. Min. Pars I. p. 160.)

127. According to this author, muscle in all parts of the body may be resolved by careful dissection into fibres of great delicacy, but pretty uniform in form and general appearance, as well as in dimensions. Their diameter does not seem to exceed the forty-thousandth part of an inch; and although they are very variable in their length, some of them, it would seem from Prochaska's observations, extending nearly three feet, they preserve the same diameter throughout. They seem all more or less flattened or angular, and have no appearance of hollowness, but are solid diaphanous filaments. Prochaska seems to have no doubt that these fibres, or fila carneae, as he calls them, are incapable of farther division.

On this supposition we may call them the primary Anatomy, muscular fibres.

128. The primary fibres are placed parallel and close to each other, and in every species of muscle, it would seem, are united, in the first place, into fasciculi of a certain size. These, in a transverse section, always appear polyedrous; and in the representation which Prochaska has given of them, as seen through a microscope magnifying the diameter two hundred times, the largest of them does not exceed an eighth of an inch, and the smallest is not below a sixteenth. In point of length they are various; but Prochaska affirms, that he has traced them extending, unbroken, and unconnected with any other fasciculi, from one end to the other of the sartorius muscle, which is one of the longest in the body.

129. These fasciculi, which we may call primary, are generally found united together into longer fasciculi; which may be denominated secondary, and these often into ternary, and so on.

130. A chemical analysis of human muscle is still a desideratum.

IV. THE ANATOMY IN GENERAL OF SKIN.

131. Except the mouths of the sebaceous follicles, we do not believe that any pores are visible on the external surface of the skin, either with the naked eye or with the microscope. We can perceive no appearance of them even at the points from which the hairs spring; the hairs seem to fill up completely the canals through which they pass.

132. The inner surface of the skin, in almost all parts of the body, exhibits a number of depressions, varying in size from a twelfth to a tenth of an inch or more, producing a sort of areolar appearance.

133. The skin consists of two substances, placed one above the other, in the form of layers or laminae. The inner lamina is called true skin, the outer, cuticle, epidermis, or scarf-skin.

134. We have found that the best and easiest mode of separating these two from each other, for particular examination, is to preserve a piece of skin, either on the recent subject or detached from it, carefully from moisture, but not so as to render it dry and hard. At the end of a week, or ten days, or more, according to the temperature of the air, such a degree of decomposition has in general taken place between the cuticle and true skin, as enables us to separate the former, with the slightest oblique pressure with the point of the finger.

135. The intimate structure of the true skin is quite peculiar. It seems chiefly made up of a species of very small dense fibres, somewhat resembling the fibres which compose the outer coat of an artery, which are closely interwoven with each other, and more firmly compacted together the nearer they are to the outer surface.

136. The outer surface of the true skin is more vascular than the internal parts; and this surface seems to owe its colour entirely to the blood circulating in its vessels.

137. The absorbent vessels of the true skin are so large and so numerous, that after they have been injected with mercury, the outer surface exhibits an exceedingly minute net-work of tubes. We

ANIMAL.

138. The cuticle is transparent, and of a slightly yellowish-grey colour. The colour of the outer surface of the true skin is, therefore, seen through it; and we have no doubt that the colour of the surface of the body, in the inhabitants of this country, and of Europe in general, depends entirely on the colour of the outer surface of the true skin, blended with the slight tinge of grey from the cuticle.

139. In almost all persons in health, there are certain parts of the soles of the feet, in which the epidermis is divisible into layers; but this seems to be purely the effect of compression; which accumulates into a thick stratum those portions of the cuticle which are constantly separating from its surface, and which, in other parts of the body, are immediately removed. This laminated appearance is never seen in the soles of persons who have been long confined to bed, or in those who, from accident or disease, have not been able to put the foot to the ground. The cuticle, in other parts of the body, does not exhibit the slightest appearance either of laminae or fibres.

140. This part of the skin is entirely destitute of blood-vessels, absorbents, and nerves. It is truly a non-vascular part, like the enamel of the teeth.

141. It is well known that when a piece of cuticle is plunged into pure nitric acid, it instantly acquires a yellow colour. In the course of twenty minutes or so, we have found, that it becomes thicker, softer, and more opaque; in twenty-four hours it is reduced to a yellowish pulp; and in about a month or six weeks it is almost entirely dissolved. Pure muriatic acid acts upon it somewhat in the same way; but less powerfully, and less speedily. Pure sulphuric acid immediately gives it a deep brown colour; in the course of twenty hours, renders it thicker and more elastic; and, after the lapse of several weeks, reduces it to the state of a very thin deep brown pulp.

142. We have satisfied ourselves, by a variety of dissections, that there is in the Negro, Caffre, and Black Mem.-Malay, a black membrane interposed between the epidermis and the true skin, upon which the dark colour of these people entirely depends. This membrane sometimes peels off with the cuticle, and sometimes adheres to the true skin. It is more tender than the cuticle, and thinner; but, like it, is entirely without vessels, and without any appearance of holes, or plates, or fibres. We conclude, that in all black men there is a similar membrane, to which their dark colour is owing.

143. After the strictest examination, however, we have not been able to discover any light-coloured membrane or pigment, such as has been described under the name of rete mucosum, between the cuticle and true skin, in the inhabitants of this country, nor in those of other European nations resembling them in colour. We have sought for it in every way, but without success. We are disposed, therefore, to deny its existence. The cause of the light colour of the skin in fair people has been already explained. (Sect. 138.)

144. Whether there be any brownish membrane in tawny people, like the black membrane in the negro, we have had no opportunity of ascertaining.

V. THE ANATOMY IN GENERAL OF HAIR.

145. We call the root of a hair, not only that part of it which is contained in the bulb, but the portion which is lodged in the skin. The middle part and the point are the parts which project beyond the surface of the skin.

146. All the hairs in the body seem to be cylindrical, and taper regularly from the root to the point.

147. Of whatever colour they be, the root is always whitish, and transparent, particularly that part of it which is lodged in the bulb. This part, too, is always much softer than the rest; the very extremity being almost fluid.

148. As far as we can judge from microscopical observations, the hairs seem to be quite solid. We have never seen any appearance of cells, or canals, or laminae, or fibres, in any part of them. In the whiskers of the seal, however, the part of the root of the hair which is lodged in the bulb, contains a conical cavity; and we suspect it is the same in human hair.

149. Dr Brewster has ascertained that hairs depolarise light, and possess the most perfect neutral axes; the axes being parallel and perpendicular to the axis of the hair. (Phil. Trans. 1815.)

150. The chemical properties of hair have been very minutely investigated by Vauquelin. (See Annales de Chimie, Vol. LVIII., and Nicholson's Journal, Vol. XV.)

151. Judging by analogy, from the structure of the bulbs of those large hairs which form the whiskers of such animals as the seal, we should imagine that the bulbs of the human hairs consisted of two coats or tunics; an inner one of a tender consistence, very vascular, and embracing immediately the root of the hair; and an outer, firmer, and less vascular one, closely surrounding the former.

152. The bulbs of the hairs are always situate under the true skin; but so close to its inner surface, that no part of the hair is perceptible between it and the bulb. Immediately after leaving the bulb, the hair is received into a canal in the true skin, which is constantly observed to be more or less oblique. A small hole in the cuticle corresponds to this canal; and the hair passing through it also, reaches the outer surface of the skin. In its passage through the true skin, we believe that it adheres to the sides of the canal, just as epidermis would do.

VI. THE ANATOMY IN GENERAL OF CARTILAGE.

153. On careful examination of this substance with the microscope, it appears to us to be uniform and homogeneous in its structure, like jelly, and without fibres, or laminae, or cells.

154. In its purest form, no blood-vessels are seen in it, nor can they be injected even with the finest colouring matter. In those pieces of cartilage, however, which are attached to the edges or extremities of growing bones, blood-vessels of considerable size may often be seen ramifying, even without the aid of injection. 155. The chemical properties of cartilage have not yet been sufficiently investigated. In its purest form, we believe that it is entirely soluble in boiling water, and acids seem to act on thin dried slices of it nearly as they do on cuticle.

VII. THE ANATOMY IN GENERAL OF BONE.

156. The structure of this substance is exceedingly simple. Divide it, and examine its surfaces with a common magnifying-glass, or cut off slender films of it, and inspect them in a powerful microscope, and it will appear to be a uniform substance without fibres, plates, or cells, penetrated everywhere by delicate blood-vessels.

157. The sulphuric, nitric, muriatic, and acetic acids, when properly diluted, soften bone, and render it pliable, without its being possible to discover, by the most minute inspection, that a single particle of its substance has been removed.

158. Calcination produces just the reverse effects. If a bit of bone be placed in a charcoal fire, and the heat be gradually raised to whiteness, it will first burn with a flame, and then become quite red. If it be now removed carefully, and slowly cooled, it will be found to have been rendered as white as chalk, and exceedingly brittle. Still not a particle of the substance will appear to have been destroyed.

159. With respect to the chemical properties of this substance, we have only to remark, that we are convinced from experiment, that the fat which has been considered as an ingredient in bone, and which is extracted from it by boiling in water, is no part of the osseous substance, but an adventitious admixture either from adipose substance without, or from marrow within.

160. We have often endeavoured to discover sulphate of lime in the acid solution both of calcined and uncalcined bone; but always without success.

VIII. THE ANATOMY IN GENERAL OF TENDON.

161. Bichat has described this common texture under the name of Système Fibreux. (Anat. Génér. III.) The term is objectionable, however, because it is equally applicable to nerve, muscle, or even cellular substance, as to the texture to which he has applied it.

162. Its distribution is very various, and very extensive. It forms not only those appendages to muscular fasciculi, called tendons, from which it has received its name, but also ligaments, periosteum, aponeuroses, fasciae, membranes, &c.

163. It appears to be chiefly composed of very delicate, white, silvery-looking fibres, collected into fasciculi, which are united with each other in various ways. Sometimes they are tied together longitudinally; at other times, interwoven almost with the same regularity as the threads in a piece of cloth; and at other times intermingled in every direction.

164. The sulphuric, nitric, and muriatic acids, act upon it very nearly as they do upon cuticle. The instant it is plunged into either of them, it shrinks up, and becomes semitransparent and elastic, just as it does in boiling water, but in a much greater degree. The effects of the pure fixed alkalies upon it are singular. At first, they operate upon it somewhat like the acids just mentioned; but, instead of dissolving it after a little while, as these do, they seem to produce very little further change upon it for a considerable length of time. If, in this state, we remove it from the alkali, and pull its parts gently asunder, its delicate fibres will unfold themselves very readily, exhibiting at same time very bright prismatic colours.

IX. THE ANATOMY IN GENERAL OF SEROUS MEMBRANE.

165. A successful injection of size or turpentine, coloured with vermilion, brings into view so many capillary blood-vessels in this membrane, that one would be almost inclined to suppose, that it was entirely composed of arteries and veins. By proper management, however, absorbents may be injected in it with quicksilver to an equal degree of minuteness. There can be no doubt, therefore, that it is chiefly composed of these two systems of vessels. Whether it contain any thing else but vessels, remains to be ascertained. Nerves have not yet been traced into it, although they may be often seen ramifying abundantly on the parts with which its external surface is connected.

X. THE ANATOMY IN GENERAL OF SYNOVIAL MEMBRANE.

166. Bichat has enumerated a variety of circumstances, in which he conceives, that the serous and synovial membrane differ from each other. (Anat. Génér. IV.) It seems to us very doubtful, however; whether all these points be well founded; at all events, we do not think that any of them can with propriety be adopted as the basis of an anatomical distinction.

167. Synovial membrane resembles serous membrane, in so far as it is a thin substance, having one smooth free surface, turned towards certain cavities of the body, and another connected by delicate cellular substance to the sides of these cavities, or to the parts contained in them. It resembles this substance also in being transparent.

168. But it differs from serous membrane in the following circumstances:—In the first place, it is a substance possessing very little vascularity in its healthy state; none of its blood-vessels are almost ever seen filled with blood after death, nor can they be made to receive the finest injection. In the second place, its absorbents are quite incapable of demonstration. Thirdly, very delicate fibres, like those of cellular substance, or like the finest filaments of tendon, are distinctly perceptible in it after slight maceration. Fourthly, it is considerably inferior in strength to serous membrane. PART III.

THE ANATOMY OF THE SKELETON.

ARTICLE I.

GENERAL OBSERVATIONS ON THE SKELETON.

I. In the Adult Male.

169. The skeleton of the body may be regarded as the solid frame-work which supports and contains the softer parts.

170. It is made up of 254 separate pieces of osseous substance, most of which contain a quantity of a matter called marrow, and are surrounded with a membrane denominated periosteum. These separate pieces, with their appendages, have the appellation of bones usually applied to them; and they are connected to each other in various ways.

1. Of Bones in their separate State.

A. Their Osseous Substance.

171. In almost all bones, the osseous part presents itself under two forms. Externally it assumes the form of an uninterrupted shell or covering, which is called the compact part, and a very delicate texture of fine plates or fibres intersecting each other, and leaving small spaces between them, projects internally from this, which is called the cellular or reticulated part. The proportion of these two, varies in different bones.

B. Of the Marrow.

172. The chemical properties of the oily matter of the marrow, have not yet been sufficiently investigated.

C. The Periosteum.

173. This covering distinctly possesses the structure of tendinous substance.

174. We cannot regard it as correct, that it is prolonged from one bone to another over joints. In general it covers the whole outer surface of the compact substance, except at those points where one bone is united to another.

2. The Connections of Bones.

175. The connections between bones are of two kinds; some admit of motion, others do not.

A. Connections admitting Motion.

176. It may be remarked of those bones which are united in such a manner as to enjoy motion on each other, that their touching surfaces never consist of bare osseous substance, nor even of osseous substance covered with periosteum. They are either provided with separate crusts or prolongations of cartilage, the surfaces of which play directly on each other, constituting what is denominated a joint or articulation; or they are united to one common intermediate substance, which is flexible, or admits of compression.

a. Articulations or Joints.

a. The Cartilages.

177. The surfaces of the portions of cartilage, which are in contact with each other in this mode of connection, are always as smooth as the finest polished ivory.

178. It was affirmed long ago by Dr Nesbit (Human Osteology), and Dr Hunter (Phil. Trans. 1743), and has been much insisted on of late years by Bichat (Anat. Génér.), that these surfaces are covered with a very delicate prolongation of synovial membrane. We are very much inclined to think, however, from a number of experiments, that these anatomists have been mistaken.

b. The Ligaments.

179. All articulated bones are partly held together by means of ligaments. These are composed of tendinous substance, and may be divided into fascicular and capsular. The fascicular ligaments are disposed in cords, at intervals, around the joint; the capsular form a continuous web, including the united surfaces in a kind of shut sac.

γ. The Synovial Membrane.

180. In all the intervals between fascicular ligaments, portions of synovial membrane may be distinctly seen filling up these intervals. They are attached to the ligaments on the one hand, and to the articulated bones on the other, just at the edge of the cartilaginous surfaces.

181. It does not seem to us, however, to have been yet satisfactorily ascertained, whether this synovial membrane be continued over the inner surface of the fascicular ligaments; or how it is disposed in joints, of which the ligaments are of the capsular kind.

b. Without Articulation.

182. The small bones of the spine called vertebrae, are united to each other chiefly in this way. The portions of them denominated their bodies, are directly connected to pieces of a flexible and compressible substance, somewhat between cartilage and tendon in its nature, one piece being common to two vertebrae.

B. Connections not admitting Motion.

183. These may be divided into two kinds, suture and synchondrosis.

a. Suture.

184. In this species, the bones are united by direct contact of their osseous substance. The contiguous parts, however, are in general more or less indented or serrated, the projecting parts of the one being fixed into holes or grooves in the other. The periosteum passes across the line of junction, and does not dip down between the united surfaces.

b. Synchondrosis.

185. In this mode, a piece of cartilage, or some 3. Dimensions and Weight of the Skeleton.

186. The height of the skeleton of a person five feet eight inches, we believe, will be found in general to be about five feet seven inches.

187. Soemmerring (De Corp. Hum. Tab. I.) has made some trials of the weight of the skeleton; and, according to him, it varies from 150 to 200 ounces. But we are uncertain as to the weights he employed, and ignorant of the manner in which his estimates were made.

II. In the Adult Female.

188. The same general remarks which have just been made with respect to the skeleton of the adult male, apply equally to that of the adult female; only the skeleton of the latter is a little lower, and not so heavy. According to Soemmerring, it weighs in general only from 100 to 150 ounces.

III. Before and after Maturity.

189. Parts corresponding to the skeleton may be distinctly perceived in an embryo of seven or eight weeks. At this early period, however, osseous substance has not yet appeared. In the place of the future bones, we find either a pellucid substance like jelly, moulded into their general form, and surrounded with periosteum, or else a simple membrane resembling the periosteum in structure. Some bones are wholly gelatinous, others wholly membranous, and others partly in the one state and partly in the other.

190. About the end of the second month after conception, the process of ossification begins. It does not commence, however, in all parts of the skeleton at once, but takes place at different periods in different bones, or even in different parts of the same bone. Its commencement in some is delayed until a considerable time after birth.

191. When we attend to the progress of ossification in those parts of the fetal skeleton which are at first gelatinous, we observe, that if any of these parts are converted into osseous substance so early as the second or third month after conception, they seem to undergo very little previous change of consistence. If they are not ossified, however, till the fourth or fifth month, they gradually lose their resemblance to jelly, becoming firmer, more elastic, and more opaque; and if the ossification is still further delayed, their opacity, firmness, and elasticity, rapidly increase, they acquire a pearly colour, and are converted into a substance in every respect the same as cartilage.

192. When the ossification commences in this gelatinous or cartilaginous basis, the first part which is ossified is always observed to be situated towards the centre of the jelly or cartilage; and from this point the process gradually extends in every direction. In early ossifications, the parts are so minute, that it is difficult to perceive the appearances in the gelatinous basis which immediately precede the formation of the osseous substance. But in those which commence at a later period, the parts of the cartilage which are just about to be converted into bone, uniformly exhibit a considerable degree of vascularity; and a number of little red specks are observed in them, in each of which a capillary blood-vessel seems to terminate, and in which the first bony particles that are formed generally appear.

193. When ossification commences in a membranous part of the fetal skeleton, the osseous substance first appears in the form of a fine net-work of slender fibres, confined to a small spot in the middle of the membrane. But by the formation of additional osseous particles, this net-work is converted into a plate of bone of extreme thinness and delicacy, and having a layer of the membrane covering each surface, which may be regarded as its periosteum. Innumerable bony fibres are then observed to shoot out, in a radiated direction, from the margins of this little plate, and these are soon connected by short transverse threads of osseous substance, in such a manner, as to give the bone for a time a slightly reticular appearance. The spaces between the fibres seem entirely filled up by blood-vessels.

194. In this manner, the ossification extends through the whole membrane, splitting it, as it proceeds, into two layers, which become the periosteum of the opposite surfaces of the new bone, but remain united into one single membrane around the whole of its margin. At the same time, however, that the bone is thus enlarging in breadth, it is also increasing in solidity, from the deposition of new osseous particles between those already formed. At last, it assumes the form of a continuous plate of compact substance, the different parts of which are proportioned in their thickness to the corresponding parts of the future bone; and if the adult bone contains any reticulated substance, the cells are generally developed in the middle of this compact plate.

195. No sooner are the cancelli developed in any part of a young bone, than they are lined with a very vascular medullary membrane. This membrane, however, contains only a slightly viscid, reddish, and transparent fluid. It does not appear to begin to receive any admixture of oil till after birth. At first, the proportion of oily matter is small, and it increases in general so gradually, that the fluid does not acquire the consistence or composition of true medullary oil, until the period of maturity.

196. In old persons, the medullary membrane seems to become less vascular, and the oil acquires a yellower colour.

197. The periosteum in the fetus is much thicker, and more tender than in the adult. It is more vascular too, and particularly at those parts of a bone where active ossification is going on. In old persons, it is thinner and less vascular.

198. As soon as the soft rudiments of the future bones are visible in the fetus, divisions may be observed in them corresponding to the articulations and synchondroses, but none to the sutures.

199. The ligaments and synovial membranes in the young person seem to differ in size only from those of the adult. 200. For a considerable time after the margins of bones, that are intended to be united by suture, first come into contact, they adhere so slightly to each other, that the bones seem chiefly held together by the periosteum which passes from the one to the other. By degrees, however, as the bones are more fully developed, they are locked more firmly into each other.

201. The apparatus of the articulations seems to undergo very little change in the decline of life. But it is not unusual, in very advanced age, to find the cartilages partially converted into osseous substance. On the approach of old age too, we may almost always observe that the sutures begin to be obliterated. Particles of osseous substance are formed between the margins of the bones, the line of the suture is gradually filled up, and at last the bones are fairly continued into each other.

ARTICLE II.

THE ANATOMY OF PARTICULAR PARTS OF THE SKELETON.

202. On this subject we have nothing which we think it necessary to add, at present, to what has been said in the body of the work. See Anatomy, from § 11. to § 72.

PART IV.

OF THE ANATOMY OF MUSCLES ATTACHED BY BOTH EXTREMITIES TO THE SKELETON.

203. In the article Anatomy, Part I. Chap. II. Sect. II. in the body of the work, the names and attachments of those muscles, which are connected to the skeleton by both their extremities, are given in the form of a table. No description accompanies this tabular view, of the form or structure of the muscles; but considering the length to which such a description would necessarily extend, we are rather inclined to think that the subject has been treated in that article with a sufficient degree of minuteness for a work like the present.

PART V.

1. OF THE ANATOMY OF THE EYE, EAR, NOSE, MOUTH, PHARYNX, FASCLE, AND INTEGUMENTS, &c. OF THE HEAD.—2. OF THE CAVITIES OF THE THORAX AND ABDOMEN; OF THE VISCERA CONTAINED IN, AND CONNECTED WITH, THESE CAVITIES; AND OF THE FASCLE, INTEGUMENTS, &c., OF THE TRUNK.—3. OF THE FASCLE, INTEGUMENTS, &c. OF THE EXTREMITIES.

We have a few observations to offer on some of the subjects comprehended in the first and second sections of this title.

BOOK I.

OF THE ANATOMY OF THE EYE, EAR, NOSE, MOUTH, AND PHARYNX.

CHAP. I.

OF THE EYE.

204. Under the general denomination of the eye is included the eye-ball, the optic nerve, the muscles of the eye-ball, the eye-lids, the eye-brows, the lachrymal gland, and the lachrymal passages. We have only a few observations to offer on the eye-ball.

Of the Eye-ball.

205. The average dimensions of the eye-ball have not yet been satisfactorily ascertained.

206. By chemical analysis, Berzelius obtained from the fluid of the vitreous humour the following ingredients:

| Water | - | - | - | 98.40 | | Albumen | - | - | - | 0.16 | | Muriates and lactates | - | - | - | 1.42 | | Soda, with animal matter soluble only in water | - | - | - | 0.02 |

100.00

The particulars of the analysis, however, are not detailed. (See Med. Chir. Transact. III.)

207. We are not yet in possession of any measurements of the lens that are more accurate or particular than those of Petit. According to him the breadth of the lens is 4 lines, and the thickness 2 lines; the radius of the anterior surface is from 6 to 8 lines, and of the posterior from 4½ to 5½ lines. (Mém. Roy. Acad. Sci., Par. 1730.)

208. We have ascertained, by many experiments, that the Morgagnian liquor, which has been so often described as surrounding the substance of the lens, immediately within the capsule, does not exist in the eye immediately after death. It seems to be the product either of transudation or decomposition.

209. By chemical analysis, Berzelius obtained the following ingredients from the substance of the lens:

| Water | - | - | - | 58.0 | | A peculiar matter | - | - | - | 35.9 | | Muriates, lactates, and animal matter, all soluble in alcohol | - | - | - | 0.24 | | Animal matter soluble only in water, with some phosphate | - | - | - | 0.13 | | Residuum of cellular membrane | - | - | - | 2.4 |

100.0

210. With respect to the peculiar matter here mentioned, Berzelius remarks, that when coagulated by boiling, the coagulum possesses all the chemical properties of the colouring matter of the blood. (Med. Chir. Transact. III.)

211. The result of his analysis of the aqueous humour is the following:

| Water | - | - | - | 98.10 | | Albumen | - | - | - | a trace | | Muriates and lactates | - | - | - | 1.15 | | Soda, with mineral matter, soluble only in water | - | - | - | 0.75 |

100.00 212. We have been led of late, from some physiological considerations, to entertain doubts whether the little dark spot in the retina, which has usually been described under the name of the central hole, be really a hole or not. Is it certain that it is not a spot which is more transparent than the other parts; so that the dark surface of the choroid coat is better seen through it, giving it the appearance of a hole?

213. The black pigment lining the inner surface of the choroid coat and iris, is, according to Berzelius, a powder, insoluble in water and acids, but slightly soluble in alkalies. When dried and ignited, it burns as easily as a vegetable substance, and the ashes contain much iron.

214. The colour of the iris does not seem to depend in the least on this pigment; but entirely on the structure of its anterior surface.

215. A delicate membrane was many years ago described by Demours and Descemet, as lining the whole inner surface of the cornea, and prolonged over the anterior surface of the iris; and the merit of having discovered this membrane was the subject of very keen controversy between these two individuals. (Portal's Hist. de l'Anat. &c. Tom. V. p. 226.) The same description has been repeated by Bichat, in his Anat. Descrip. Vol. II.

216. We have many times sought for this membrane, but in vain; and are much disposed to think, that the anatomists mentioned have been deceived by certain appearances which occasionally present themselves on the inner surface of the cornea, when it has been macerated, and begins to decompose.

217. In almost all anatomical writings, the conjunctiva is still described as continued over the anterior surface of the cornea. It is impossible, however, to demonstrate this in the recent eye; and the substance which may be peeled off from the anterior surface of the cornea after slight maceration, is obviously a stratum of the cornea itself. This distribution, therefore, of the conjunctiva, which has been copied by one author from another, is a mere hypothesis; and one which, in our opinion, is not much more probable, than that the cornea is covered with a crust of bone.

CHAP. II.

OF THE EAR.

218. The structure of several of the soft parts of the ear seems to us to require further investigation. We have most doubts, however, as to the accuracy of the descriptions hitherto given of the contents of the labyrinth.

219. Soemmerring has, within these few years, published a very elegant and very interesting work in German, on the structure of the human ear; in which all the parts of this complicated organ are represented in engravings.

220. His description of the labyrinth corresponds pretty nearly with that which had before been given by Scarpa. We believe it, however, to be more accurate; and his representations are certainly more natural.

221. The whole inner surface of the labyrinth is said to be lined with a very delicate membrane, which sometimes exhibits an appearance of considerable vascularity, and adheres everywhere to the bone. Within this are found, in the vestibule, two membranous sacs, which do not seem to have any communication with each other; but from the larger one, which is more oblong than the other, three membranous canals extend into the three semicircular canals of the bone.

222. The membranous sacs, and the membranous canals, appear to contain a thin watery fluid; and between them and the vascular lining of the labyrinth already mentioned, a small quantity of a similar fluid seems to be interposed.

223. The portion of the auditory nerve destined for the vestibule, seems to be entirely lost on these sacs and canals.

224. We are not fully satisfied with the descriptions usually given of the aqueducts of the labyrinth. They have been too generally examined in the young subject. Are they always open in the adult; and, when open, are they distinctly lined with any peritoneal covering?

CHAP. III.

OF THE NOSE.

225. The membrane lining those parts which contribute directly to form the cavities of the nose, possesses the same structure everywhere. Its free surface is vascular, red, and villous; the surface attached to the bones or cartilages, smooth, and silvery, like tendon. It is obviously composed of two distinct textures; but they are so closely united, that it is impossible to separate them from each other.

226. The membranes lining those cells and sinuses which communicate with the cavities of the nose, is a good deal different. It is thinner, more tender, paler, semitransparent, and promising little vascularity. Its free surface is less villous, and the surface attached to the bones does not exhibit any tendinous appearance.

227. Bichat's description of this membrane (Anat. Descrip. II.) is by far the best which has yet appeared.

CHAP. IV.

OF THE MOUTH.

228. When the jaws are closely shut, the mouth may be regarded as consisting of two regions; an external and an internal, separated from each other by the teeth and gums.

229. The external region is formed by the cheeks and lips without, and by the teeth and gums within. The internal region is bounded before, and laterally by the teeth and gums; below by the tongue; above by the hard palate; and behind by the soft palate. Between the soft palate, however, and the posterior part of the tongue, there is an opening, variable in its dimensions, according to the will of the individual, which leads into the pharynx or fauces. This is called the pharyngeal orifice of the mouth, or the isthmus of the fauces.

230. The cheeks and lips are formed of the following parts. 1. An inner membrane of a peculiar Anatomy, structure. 2. Little bodies called labial and buccal glands, situated immediately without the inner membrane; the former opposite the front teeth of both jaws; the latter opposite the grinding teeth of the upper jaw. 3. Various muscles. 4. Bodies called parotid glands, one on each side. 5. Cellular and adipose substance. 6. Skin. 7. Hairs. 8. Branches of various blood-vessels, absorbents, and nerves, supplying these parts.

231. The gums consist of a peculiar membrane attached directly to the alveolar arch of both jaws, and to the collars of the teeth.

232. The tongue is composed of the following parts. 1. A peculiar membrane continuous with the gums. 2. Under this, towards the root of the organ, lingual glands exactly like the labial glands. 3. Various muscles. 4. Two submaxillary, and two sublingual glands; one of each on each side. 5. Cellular and adipose substance. 6. Blood-vessels, absorbents, and nerves, supplying all these parts.

233. The hard palate is formed by the inferior surface of the palatine processes of the palate and upper jaw bones, lined by a membrane continuous with the gum, and similar to it in structure.

234. The soft palate is formed of a peculiar membrane, which lines both its anterior or oral, and its posterior or pharyngeal surface; of little glands, which may be called palatine, similar to the labial glands of various muscles; and of two bodies called tonsils, one on each side.

CHAP. V.

OF THE PHARYNX.

235. Into this cavity at the top, and on the fore part, the right and left cavities of the nose open; the two orifices being denominated the pharyngeal orifices of the nose. Immediately below, is the soft palate; and to this succeeds the pharyngeal orifice of the mouth. Below this orifice, again, is situated the opening of the glottis, with the epiglottis on its upper and fore part; and under this, there is a slight convexity, which terminates the pharynx before.

236. On each side of the pharynx, at the very top, are found the orifices of the Eustachian tubes, leading from the tympana of the ears.

237. There are no orifices on the posterior surface of the pharynx. This surface is smooth and slightly convex. A considerable portion of it may be seen through the pharyngeal orifice of the mouth, when the mouth is held wide open, opposite to a mirror.

238. The roof of the pharynx is formed by a membrane similar to that which lines the hard palate; which is attached directly to the lower surface of the basilar process of the occipital bone.

239. The posterior and lateral parts are lined with a membrane like that covering the inner orifice of the cheeks; and exterior to this is a coat of muscular fibres, belonging to three muscles called constrictors of the pharynx, two called stylo-pharyngeal, and two denominated palato-pharyngeal. This muscular coat is connected by means of cellular substance behind, to the bodies of the upper cervical vertebrae; the long and short recti muscles of the head, and the longi colli; and laterally, to the carotid arteries, internal jugular veins, pneumo-gastric nerves, &c.

240. The convexity under the glottis, on the fore part of the pharynx, is covered with a membrane similar to that lining the other parts, but rather paler. This is attached by means of cellular substance to the crico-arytenoid muscles of the larynx, and to the posterior margin of the thyroid cartilage on each side; and it is continuous above with the inner membrane of the glottis.

BOOK II.

OF SOME OF THE VISCERA CONTAINED IN THE CAVITIES OF THE THORAX AND ABDOMEN, OR CONNECTED WITH THESE CAVITIES.

CHAP. I.

OF THE LUNGS AND THEIR APPENDAGES.

Section I.

Of the Lungs.

241. These organs may be regarded as consisting of two parts; a peculiar substance, and a serous membrane called pleura, covering the whole outer surface of this substance.

242. The substance of the lungs is composed of cells called air-cells, through which certain tubes called bronchial tubes, together with blood-vessels, absorbents, and nerves, are found ramifying in every direction.

243. Nothing certain is known respecting the form or dimensions of the air-cells. When examined with a magnifying-glass, in their collapsed state, they appear very irregular in their shape.

244. It is still uncertain, too, whether they communicate directly with each other by lateral openings, or otherwise. Towards the surface of the lungs, they are obviously collected into a number of separate clusters, which are surrounded by common cellular substance, and have no communication with each other. For, if air be thrown into the bronchial tube supplying one of these, it will not inflate the other. Whether the arrangement be similar throughout the whole substance, we do not know.

245. The bronchial tubes ramify throughout the substance of the lungs exactly like an artery. There is no doubt that they all terminate at last in the air-cells; but they are too minute to be traced by dissection so far. We are rather inclined to think, from an examination of corroded preparations of the injected bronchial tubes, that each air-cell is supplied with a distinct branch of these vessels.

246. The arteries and the veins of the lungs admit of being injected to a great degree of minuteness; but no method has yet been discovered by which we can see the precise manner in which they end or begin, and the distribution of their terminations and origins, with respect to the air-cells. We learn nothing satisfactory by injecting a thin fluid, such as water, into either of these systems of vessels, and finding that it flows out by the bronchi; or by throwing it into the bronchi, and observing that it returns by the blood-vessels. Transudation admits of fluids pas- Section II.

Of the Appendages of the Lungs.

247. These are the larynx, the trachea or windpipe, and the thyroid gland.

248. The larynx contains two compartments, an upper and a lower, which communicate with each other by a narrow passage. The upper compartment is usually called glottis; and the aperture by which it communicates with the lower one, the rima of the glottis. The edges of this slit are pretty sharp; and the term vocal cords has frequently been applied to them. It seems to us better, however, to relinquish this appellation: since it implies an hypothesis with respect to the functions of the rima of the glottis, which, if not incorrect, is at least very doubtful.

249. We have not been able to discover any structure resembling longitudinal muscular fibres in the trachea or bronchi. The whitish lines which are seen running along the back part of the windpipe when it is slit open towards its lower end, and which extend into the bronchi, depend on a peculiarity in the structure of the inner membrane. These are the lines, however, which, we suspect, have been mistaken for muscular fibres.

250. It is a remark which we believe was first made by Bichat, (Anat. Desc. II.) that the thyroid gland, although it be supplied with large arterial trunks, is not a very vascular organ. It always contains less blood after death, than many other organs, which do not seem, proportionally, to have such large blood-vessels. We have had occasion to verify this observation very often.

CHAP. II.

OF THE ALIMENTARY CANAL.

251. An exceedingly interesting paper on the appearances of the stomach immediately after death, by Dr Yelloly, will be found in the Medico-Chirurgical Transactions, Vol. IV. The facts he has ascertained, seem to us to constitute by far the most important addition to our knowledge in this department of anatomy, which has been made for many years. We had directed our attention to this subject, for some time previous to the appearance of Dr Yelloly's valuable essay; and we have lost no opportunity since, of prosecuting the inquiry. We are happy to find, that our observations correspond almost entirely with those of Dr Yelloly.

252. This very judicious and intelligent physician has found, that appearances of vascular fulness in the inner surface of the stomach, whether florid or dark-coloured, in distinct vessels, or in extravasations of various sizes, occur in every variety of degree and character, under every circumstance of previous indisposition, and in situations where the most healthy aspect of an organ might be fairly expected. They are found in every part of the stomach, but principally in the posterior part of the great end, and in the lesser curvature; and they cover spaces of various extent, but are generally well defined, and terminate abruptly.

253. These appearances preserve their distinctness for a short time only, being best marked on the first day, and soon after; but at irregular periods, becoming more obscure, the parts which were vascular, acquiring a dark red or purple tinge, which loses itself gradually. This effect more readily takes place, when the villous coat is in contact with a fluid, particularly water. They exist in the body of the villous coat, and, in general, appear to be greatest, where that membrane is the least firm and resisting. Careful dissection discovers a fine net-work of veins, between the villous and the muscular coat, from which the minute vascularity of the former evidently proceeds. The arteries are always empty, or very nearly so.

254. The vascularity now mentioned, often possesses a starred appearance, from the circumstance of its spreading in minute vessels, continually ramifying into smaller ones, so very near the extremity of the villous surface. A slight degree of friction with the point of a scalpel, will open the minute extremities of the vessels; but Dr Yelloly has never observed, that, even by squeezing the larger branches, in a retrograde way, effusion into the cavity of the stomach could be produced, so as to stain a white substance, which might be applied to the villous surface.

255. Dr Yelloly has remarked, that the coats of thickness of the stomach vary very much in thickness in their different parts; the whole substance being sometimes so thin at the great end, as readily to admit of making out through it, dark figures on a light surface. This difference he conceives is produced by variations, both in its villous and muscular coats; for he found, that of two equal oval portions of the same stomach, one of which was taken at the great end, and the other near the pylorus, in the lesser curvature, the former, weighing six grains, had its villous coat, consisting of 2½ grains, and the peritoneal and muscular together, of 3½ grains; while the latter, weighing 19½ grains, had its villous coat, consisting of 7 grains, and its peritoneal and muscular together, of 12½ grains. The thickness of the peritoneal coat appeared to be pretty uniform; but that of the muscular and villous seemed to vary, not only in different stomachs, and in different parts of the same stomach, but in relative proportion in such different parts.

256. Mr John Hunter seems to have been of opinion, that the greater thinness of the stomach here described, was the consequence of an erosion of the villous coat, by the gastric juice. We think, however, that Dr Yelloly's observations clearly shew, that it is not owing to this cause. At same time, we cannot altogether agree with this ingenious author, in considering it as certain, that the difference is one which exists during life. We have often had occasion to observe, in examining the contents of the abdomen, at various periods after death, that those portions of the small or large intestines, which happened to contain air or thin fluids, or both, were considerably thinner in their coats, than portions directly continuous with them, which were empty and apparently contracted at the time of death. The thinness of the stomach at particular parts, may be owing to the same circumstance; and it is not a little in Anatomy, favour of this conjecture, that the parts of this organ which are generally observed to be thinner than the rest, are such as must be exposed, from the usual position of the subject after death, to the contact of any air or fluids, which the stomach may chance to contain at the time death takes place.

CHAP. III.

OF THE LIVER.

257. In the descriptions which are usually given of the internal structure of this organ, a good deal is stated as fact, which we apprehend is yet matter of conjecture.

258. Besides the absorbents, which it possesses in common with other organs, four systems of vessels are distributed through it; viz. the ramifications of the hepatic artery, the hepatic veins, the portal vein, and the biliary vessels.

259. Injection enables us to trace each of these systems to a great degree of minuteness within the substance of the liver; but, the exact termination or commencement of any of them is not known.

260. In forming our opinions, in the meanwhile, on this subject, it will be proper to keep in recollection, the direction in which the fluids have been ascertained to flow within these different vessels, in the living body. By two of these systems, viz. the hepatic artery and the portal vein, blood is constantly entering the liver; and by the other two, viz. the hepatic veins and the biliary vessels, fluids are perpetually leaving this organ. It is exceedingly improbable, therefore, that the branches of the two former should communicate with each other, or those of the two latter.

261. Whether the hepatic artery and portal vein communicate with the hepatic veins alone, or with both the hepatic veins and the biliary ducts, cannot, it seems to us, be decided by simply injecting a thin fluid like water into either of the trunks, in the dead body, and observing by what channel it escapes. For, in the first place, transudation is a source of fallacy in all experiments of this kind; and, secondly, allowing that no transudation took place, a direct communication between any two of these opposite systems of vessels, might open an indirect channel for the fluid, through the branches of the other two.

262. The portal vein has been said to resemble an artery somewhat in its structure; but we have never been able to discover any similarity between them. It has always appeared to us to have the same composition as the other veins of the body.

CHAP. IV.

OF THE GRAVID UTERUS.

263. The department of this subject, which seems to us most deserving of further investigation, is the structure of the Placenta.

264. According to Dr Hunter's description of this substance (see Anatomical Description of the Human Gravid Uterus, Edit. by Dr Baillie. Lond. 1794), it consists of two portions; a foetal or umbilical, and a maternal or uterine part.

265. The foetal part is composed entirely of ramifications of the umbilical arteries, and umbilical vein. These, dividing to almost infinite minuteness, extend to all parts of the placenta. The branches of the umbilical arteries finally terminate in the umbilical vein, and they have no other termination; the branches of the umbilical vein all arise from the umbilical arteries, and they have no other commencement.

266. The maternal part, consists of a whitish-coloured substance, which is spread over the outer surface of the placenta, in the form of a membrane, and sends off innumerable irregular processes, which pervade its substance, as deep as its inner surface. These are everywhere so blended and entangled with the ramifications of the umbilical system, that it is impossible to discover the nature of their union. They are interwoven in such a manner, however, as to leave innumerable small vacuities or cells between them, which have free communications with each other, through the whole mass. The maternal part is full of both large and small arteries, and veins, none of which are derived from the vessels of the foetal part, but all from the arteries and veins of the uterus. The arteries are all much convoluted and serpentine; the larger, when injected, are almost of the size of crow-quills; and, after little or no ramification, they all terminate abruptly in the cells already described. This is their only termination. The veins have frequent anastomoses, pass in a very slanting direction, and generally appear flattened; some of them are at least as big as a goose-quill, but many of them very small; and all of them arise abruptly from the cells of the placenta. This is their only commencement.

267. This description of Dr Hunter's, has been acquiesced in pretty generally by the anatomists of this country, and we believe also by those on the Continent. It is to be observed, however, that it is partly Not susceptible of demonstration, and partly hypothetical; and we confess that we do not think that the conjectural part is altogether satisfactory.

268. In the first place, the existence of cells in the placenta, we hold to be matter merely of conjecture. If melted wax, it is said, or any similar fluid, be injected into the uterine arteries, it will first fill the cells, and then return by the uterine veins; or if it be thrown in by the uterine veins, it will fill the cells and then pass on into the uterine arteries; or if an injecting pipe be simply thrust into the middle of the placenta, and melted wax injected, the whole cells will be filled, and the uterine veins also. But it does not follow from these experiments, that the cells which appear, are cells naturally existing in the mass. They may be the effect of artificial distention of its parts from extravasation of the injected fluids; and we think it favourable to this hypothesis, that, considering the size which these cells generally have in an injected placenta, there is no appearance of them, either in a collapsed state, or filled with blood, in one which is uninjected.

269. Secondly, we regard it merely as an hypothesis, that the blood-vessels of the foetal part of the placenta do not communicate with those of the maternal part. The commencements or terminations of either system, cannot be seen; they must be deduced, either from injections in the dead body, or from observations on the state of the circu- Now, although it may be found impossible to force even a thin fluid from the umbilical arteries into any of the uterine veins, or from the uterine arteries into any of the umbilical veins, we cannot positively conclude, from this experiment, that these vessels do not communicate with each other. The same experiment often fails when tried on vessels which are known to be connected with each other. For example, there can be no doubt that the arteries and veins of the stomach communicate; yet, it is in general impossible, even with the finest fluids, to inject the one set of vessels from the other.

270. Upon the whole, therefore, we think a new series of observations on the anatomy of the placenta, very desirable. In the meanwhile, nothing seems to us to have been ascertained respecting its structure, at all inconsistent with the hypothesis, that part of the capillary branches of the uterine arteries communicate directly with corresponding branches of the umbilical vein, and part of the capillary branches of the umbilical arteries, with corresponding branches of the uterine veins.

PART VI.

1. OF THE SITUATION AND CONNECTIONS OF THE HEART, AND THE STRUCTURE AND DISTRIBUTION OF THE TRUNKS AND PRINCIPAL BRANCHES OF THE BLOOD-VESSELS.—2. OF THE STRUCTURE AND DISTRIBUTION OF THE TRUNKS AND PRINCIPAL BRANCHES OF THE ABSORBENTS, AND OF THE GLANDS CONNECTED WITH THEM.—3. OF THE SITUATION AND CONNECTIONS OF THE BRAIN AND SPINAL CORD, AND THE STRUCTURE AND DISTRIBUTION OF NERVES COMMON TO MANY PARTS.

271. We insert this general title here, merely for the sake of pointing out the place, in which we conceive the subjects enumerated in it should be treated of, in a systematic view of Human Anatomy. The progress of the science does not suggest to us any thing of sufficient importance relative to these subjects, to demand notice in the present supplementary pages.

See, for the first division of the title, Encycl. Britt. ANATOMY, Part I. Chap. IV. Sect. x. and xi.; for the second, Part I. Chap. III. Sect. xiv.; and for the third, Part I. Chap. V.

PART VII.

OF THE MODE OF INSPECTING THE BODY AFTER DEATH; AND OF THE PROCESS OF EMBALMING.

BOOK I.

OF THE MODE OF INSPECTING THE BODY AFTER DEATH.

272. This process is differently conducted, according as the death of the individual has been natural, or is suspected to have been violent.

CHAP. I.

OF THE MODE OF INSPECTING THE BODY AFTER NATURAL DEATH.

273. In this case, there is one general rule which the operator ought always to prescribe to himself; which is, that the parts to be examined should be exposed, by means of as few external incisions as possible, consistently with the speedy and complete inspection of these parts.

274. The incisions, of course, will frequently vary, according to the supposed nature of the diseased structure which is to be examined. But a few general directions may be given for conducting the process; in those cases in which inspection is most frequently required.

1. Inspection of the Cranium.

275. Make a vertical incision from ear to ear, over the crown of the head, through the scalp; and dissect the anterior flap forwards as far as the glabella, and the posterior one backwards, to a little below the occipital protuberance. Then remove the skull-cap, by sawing through the outer table of the bones, and breaking through the inner table with a chisel and mallet. This is a more expeditious mode than sawing through the whole; and it also ensures the safety of the dura mater.

2. Inspection of the Pharynx.

276. Make an incision through the middle of the lower lip down to the jaw-bone, and continue it through the integuments on the fore part of the neck, half way down, or altogether down to the top of the sternum. Saw through the symphysis of the lower jaw. Then detach the tongue completely from its connections with the inside of the jaw on either side, and so expose the pharynx.

3. Inspection of the Larynx and Trachea.

277. Make an incision through the skin from the middle of the chin, straight down to the top of the sternum. Dissect off, with the flaps laterally, the parts attached to the larynx and trachea. Then cut completely through the root of the tongue, by an incision from before backwards, beginning a quarter of an inch above the os hyoides. Next revert the larynx and trachea, either by dissecting them from the oesophagus, or taking the oesophagus along with them. The glottis is thus exposed, and the rima. Both larynx and trachea may then be slit open in the middle behind.

4. Inspection of the Chest.

278. Make an incision through the integuments, from the top of the sternum to the pit of the stomach. Dissect back with each flap all the soft parts down to the ribs. Carry the flaps backwards an inch, or an inch and a half, beyond the joining of the cartilages with the osseous substance of the ribs. Then cut through these cartilages close to this joining, beginning with the second rib, and ending with the seventh. Pull forwards the lower part of the sternum a little; introduce a scalpel behind it, and Anatomy, detach the diaphragm and mediastinum from it; then saw it through, or break it, immediately below the connection of the first rib, and the cavities of the chest will be sufficiently exposed.

5. Inspection of the Abdomen.

279. Make one straight incision from the pit of the stomach to the pubes, through the whole parietes of the abdomen at once; and then relieve the flaps a little at top, by reverting them, and cutting off the attachments of the oblique, recti, and transversales muscles, to the sternum and cartilages of the ribs. This incision will, in most instances, suffice for an examination of all the viscera in the abdomen; and it is peculiarly well adapted for cases of dropsy of this cavity, as it retains the fluids until they can be completely and conveniently removed.

280. Where a freer opening into this cavity is thought necessary, the incision from the pit of the stomach may be made to terminate at the navel, and then one may be continued on each side from that to the spinous process of the ilium.

281. If a still freer opening be required, the parietes may be divided by a crucial incision; one part of which extends from the precordia to the pubes, and the other across this at right angles opposite the navel, from one loin to the other.

282. Cases sometimes occur, in which neither of these incisions admit of a sufficiently accurate inspection of the contents of the pelvis; and, in such instances, it is necessary to remove by the saw the pubal bones on each side.

CHAP. II.

OF THE MODE OF INSPECTING THE BODY, WHEN VIOLENT DEATH HAS BEEN SUSPECTED.

283. In these circumstances, there ought to be no restriction, either as to the time employed in the inspection, or the number or extent of the external incisions.

284. The cases of this nature usually requiring a peculiar mode of procedure, are those in which death has been suspected to have been induced, either by poison administered by the mouth or rectum; or by abortion purposely brought on.

285. When poison is suspected to have been introduced into the stomach or rectum, the whole of the alimentary canal must be removed from the oesophagus to the anus, in order that its contents may be carefully examined. For this purpose, a double ligature should, in the first place, be applied to the very commencement of the jejunum, and the intestine divided between the two threads; a similar ligature should then be applied to the ilium, close to its termination in the colon, and the tube divided in the same manner. The root of the mesentery being now cut through, the whole jejunum and ilium are removed together. A double ligature is next to be applied to the rectum, as low down as possible, and the rectum, being divided between the cords, it is to be removed, along with the whole of the colon. The oesophagus, stomach, and duodenum, are then to be extracted together; taking care, first of all, to tie a ligature round the top of the oesophagus.

286. In cases where abortion is suspected to have taken place, we hold it to be a rule which should never be deviated from, that the uterus and all its appendages should be examined in situ. For that purpose, therefore, the anterior parietes of the pelvis should be freely removed.

BOOK II.

OF THE PROCESS OF EMBALMING.

287. The object of this process is to prevent altogether, or to retard the decomposition of the body after death.

288. The following method of performing it, (which is that recommended by Dr. Baillie, Transactions of a Society, &c. Vol. III.) with only a few alterations, appears to us the simplest and easiest.

289. In the first place, an antiseptic fluid is to be prepared of essential oil of turpentine, with a small proportion of Venice turpentine dissolved in it; and this is to be well charged with vermilion. The pipe of a syringe, such as is commonly employed in anatomical injections, is then to be introduced into the anterior femoral artery, with its point turned towards the heart; and as much of the antiseptic fluid is to be injected into the vessels of the body, as it is thought they will bear without rupture. A ligature being applied to this vessel, the pipe is then to be withdrawn, and re-introduced at the same opening, with its point downwards, so that the part of the limb below the groin may be completely injected. This done, the pipe is to be removed, the artery tied, and the skin sewed up; and the body is to be allowed to rest for an hour or two.

290. The cavities of the chest and abdomen are then to be laid open in the usual manner.

291. An aperture being made into the pericardium, this bag is to be filled all round the heart, with an antiseptic powder, composed of two parts camphor, one of resin, one of nitre, and a sprinkling of oil of rosemary or lavender.

292. Next, an opening is to be made into the trachea, just below the cricoid cartilage, and the lungs are to be injected with camphorated spirit of wine.

293. A ligature is then to be applied to the oesophagus at the cardia, and another to the rectum, as far down as possible; and the alimentary canal is to be emptied at proper points, between these ligatures, and as much of the air and feculent matter it may happen to contain, as possible. No water should be employed for the purpose of ablution. Camphorated spirits of wine are then to be injected upwards and downwards, so as moderately to distend the whole stomach and intestines.

294. The bladder is next to be slit open, at its upper extremity, and filled with the antiseptic powder.

295. The surface of all the viscera of the thorax and abdomen is then to be washed with camphorated spirit of wine, and all the intestines between them filled with the antiseptic powder; after which, these cavities are to be sewed up.

296. The mouth, nose, and pharynx, are next to be washed out with the camphorated spirit of wine, and stuffed as much as possible with the powder.

297. A sufficient quantity of the same antiseptic powder, is then to be introduced into the passages of the external ear, rectum, and vagina in the female. The humours of the eyes being let out, the powder is also to be employed to fill up the space between the eyes and eye-lids.

298. All these operations being completed, the surface of the body is to be rubbed over with some aromatic oil, such as oil of rosemary or of lavender.

299. Lastly, the body is to be inclosed in such a chest as shall completely exclude the external air. A chest of lead is best adapted for this purpose. Before introducing the body, a quantity of plaster of Paris should be spread on the bottom of the chest, for the purpose of absorbing moisture.

II. COMPARATIVE ANATOMY.

This department of Anatomy has, of late years, been cultivated with so much zeal, both in this country and on the Continent, that we are persuaded nothing more is necessary to render it a very favourite branch of general study, than a more elementary arrangement of the facts which it comprehends, and a more philosophical classification of the living beings to which these facts relate.

Were all the known plants in the world submitted to the examination of a certain number of individuals, accustomed to nice and patient investigation, but altogether ignorant of the botanical arrangements hitherto proposed; and were these individuals required to classify the objects placed before them, solely according to their general external resemblance, in visible and tangible properties; we imagine there can be no doubt, that precisely the same classification would at last be adopted by them all. We apprehend, indeed, that the result of the experiment would be similar, were engravings of the plants merely substituted for the plants themselves, provided the representations were sufficiently accurate in point of form and colouring. It is to such an arrangement as this, we conceive, that the appellation of natural is alone applicable.

No such classification, however, has yet been made, of the objects of the vegetable kingdom. The various natural methods which have hitherto been proposed, are all, in truth, more or less artificial; that is, founded on partial, instead of general, similitudes. This may appear, at first sight, a little extraordinary; but the causes of the defect may, we believe, be assigned with tolerable certainty.

A series of coloured representations of all the plants hitherto discovered, even if they could have been executed in the earlier periods of the art of engraving, would have constituted a work, by much too unwieldy and expensive, for the greater part of those already ardent in botanical pursuits, or who felt eager to engage in the cultivation of a science, which promises so much innocent pleasure. It became necessary, therefore, to attempt to discriminate plants from each other, by verbal description; so that botanists, in every rank of life, and in every quarter of the world, might be enabled, by the possession of a few small volumes only, to discover the name and properties of any "herb, tree, or flower;" out of the multitudes which are scattered over the surface of the earth. It was in a manner, however, essential to the success of this undertaking, that the descriptive detail should be circumscribed within narrow limits; and, accordingly, it has been the constant aim of all the botanists who have successively engaged in it, to discover some circumstances of partial resemblance among plants, which might not only form the basis of a methodical arrangement, but admit of sufficiently concise and perspicuous description.

On these principles the Sexual System of Linnæus was constructed; and there can be little doubt, that it owes its almost universal adoption to its being founded on discriminating characters, admitting of so much shorter and more intelligible description, than those of any other method which has yet been proposed. To this system, indeed, we imagine it is generally acknowledged, the science of botany is chiefly indebted, for the rapid progress it has made in modern times. By an appeal to any of those botanical works which are composed according to the Linnæan arrangement, there is no one who, after a little practice, may not be able to discover what name any particular plant he may have gathered has received, or whether any appellation at all has yet been bestowed upon it. These dictionaries, it is true, cannot communicate to him much information respecting the external form or colour, or consistence of the plant, which he has it not in his power to ascertain, in a much more satisfactory manner, by a direct examination of the object itself; and regarding the properties of the plant, they do not, in general, profess to instruct him at all. But as the motives which prompt by far the greater number of persons to the study of botany, are, the love of discovering the names of plants from the shortest possible verbal description of them, (a pleasure nearly allied to that which results from the solution of riddles,)—or a love of displaying to others the knowledge of names thus acquired;—or a great emulation to achieve the glory of detecting a plant without a name at all;—the works we have mentioned may be truly said to serve sufficiently well the general purposes of the botanist. In doing so, too, it is equally undeniable, that they contribute materially to extend our knowledge of plants. By rendering that easy, which would otherwise have been difficult of acquisition, and by converting into a pleasure, what would else have been a toil, they add to the number of those amiable enthusiasts, who are continually employed in exploring the unknown regions of the vegetable world.

To the higher and more difficult investigations of the vegetable economist, however, neither the Linnæan System, nor any classification founded on similar principles, is at all applicable. For his purposes, a perfectly Natural Method is essentially necessary; and how much sooner the botanist may feel inclined to smile at the light estimation in which we hold the difficulties of the undertaking, we confess, we cannot suppress our astonishment, that, with the aid of arts, so common and so perfect, as drawing and engraving now are, such a Method should not have been invented long before this time.

The application of these remarks to the subject of the present article, will be obvious, when we state Anatomy, that not only has no Natural Arrangement of the lower animals been hitherto attempted, but no Artificial Classification of them, even, has yet been proposed, which has met with general adoption.

The imperfections and inaccuracies of the Artificial Classification of the lower animals, by Linnæus, have long been seen and acknowledged; and it is now only matter of surprise, that the same mind which constructed the Sexual System, in one division of the living world, should have proposed an arrangement so defective and incorrect in the other. This Classification, accordingly, has been supplanted in the writings of all the more eminent naturalists of late years, by that of Blumenbach, or Cuvier, or Macartney. Of these three, it has always appeared to us, that the System of Macartney is by far the most perfect, and the most likely to be generally adopted, were its merits more extensively known. It will be found under the article Classification, in Rees's New Cyclopaedia. Zoologists, however, at present, are far from adhering universally, either to this Method of our countryman, or to that of either of the two great Continental anatomists, whom we have just named. Some give the preference to one, some to another, and there are not a few naturalists, we believe, who, in this unsettled state of the science, choose rather still to follow the Method of Linnæus, with all its faults, than to adopt the language of any System less generally known.

Whichever of these Classifications, however, or whatever similar Classification shall hereafter obtain the preference from the majority of naturalists; we apprehend that it can hardly be expected that zoology will derive such advantages from it, as have accrued to botany, from the facilities and precision of the Sexual System of Linnæus. It is an objection to all such zoological Classifications as we have alluded to, that they are founded too much on the internal structure of animals. Most of the discriminating characters hence derived, are, no doubt, sufficiently sure and precise; but some of them, it must be confessed, are very vague; and others are in no small degree uncertain. At all events, we imagine, the number of individuals is very few, out of the multitude of those with whom zoology is a favourite pursuit, who are either skilled enough in anatomy to look for these distinguishing circumstances, or, if they are, and feel an inclination to attempt the dissection, enjoy either the leisure or the dexterity necessary for accomplishing it. This department of natural history is, we fear, destined to make slow progress indeed, if the zoologist, before he can determine whether an animal be a Reptile or an Insect, must satisfy himself by a complete exposure of its interior frame, whether it have a brain and skeleton or no; or if, before ascertaining whether it be a Bird or a Fish, it be absolutely necessary for him to settle the nice question, whether its blood be warm or cold, or whether its heart have one ventricle or two. We will venture to affirm, that the general class to which any individual animal belongs, was never yet ascertained by any one naturalist, merely by an examination of the characters laid down for that class, in any one zoological arrangement that has ever been proposed.

Comparative Anatomy and Physiology, then, it would appear, labour at present under the same disadvantages, as that department of Vital Economy, which treats of the structure and functions of Vegetables. They have no Natural Classification to refer to; no arrangement founded on that principle, which never fails to bring together objects truly allied by nature, in all the circumstances of their economy, viz. a general resemblance in external properties, visible and tangible.

We feel confident, that, if such a method were constructed, it would not only greatly facilitate the study of Comparative Anatomy, but be the means of promoting a much more general investigation of the habits of many of the lower animals. On this account, therefore, we regret the more to learn, that, in the splendid work, which Cuvier has been employed for so many years in preparing for publication at Paris, the arrangement which this great naturalist proposes to follow, although different from that with which anatomists have long been familiar in his Leçons d'Anatomie Comparée, is still founded on equally artificial principles. In the article Animal, in the Dictionnaire des Sciences Médicales, he gives the following sketch of it:

"Dans un traité que nous nous proposons de publier incessamment sur le règne animal, et où nous le distribuons d'après l'ensemble de son organisation, notre première division sera en quatre grandes classes, ou phalanges; savoir: les animaux vertébrés, les animaux mollusques, les animaux articulés, et les animaux étoilés; cette division nouvelle, dont nous donnerons alors les motifs avec tout le développement qu'ils comportent, nous paraît répondre au plan de la nature beaucoup mieux qu'aucune de celles qui ont été proposées jusqu'à présent."

This outline of the New Classification, by the celebrated author himself, is not only sufficient, in our minds, to show how much it is at variance with the principles of a Natural Method, but enables us also to anticipate certain objections, which cannot fail to be urged to it, considering it even as an Artificial System. We may content ourselves, at present, with remarking, that there are very few of the animaux vertébrés, to which the appellation of "articulés," is not perfectly applicable; and many "animaux articulés," that might with as much propriety be denominated "étoilés," as those to which that epithet is intended to be restricted.

In the hope, therefore, that some naturalist, availing himself of the aid of engraving (for without this aid we are afraid the work can hardly be accomplished) will soon supply to zoology a perfectly Natural Method, we shall only further observe, that we should then be disposed to arrange the subjects which fall to be treated of in Comparative Anatomy, exactly according to the same order as we have already proposed for Human Anatomy.

The immense body of facts which this department of science now comprehends, renders it quite impossible to exhibit them in detail, and at same time to observe those limits which it is absolutely necessary to prescribe, even to articles of the utmost importance, in a general Dictionary like the present. A mere outline of the subject is all that can be looked for. Accordingly, in the body of the work (Anatomy, Part II. Chap. iv. to xii.), such an elementary and popular view of Comparative Anatomy has been given; as we have no doubt will appear to our readers altogether sufficient for the purposes of the general student. The accession of facts which the science has received within these few years would fill a volume; and, as they relate chiefly to particulars, they are unsusceptible of abridgment. For this reason, nothing remains for us to do, in the present columns, but to refer those who are desirous of prosecuting the subject more minutely, to those works, general or particular, in which the more recent progress of the science has been recorded.

The most useful elementary work on Comparative Anatomy which we yet possess, is the short system of Professor Blumenbach. This was translated into English in 1807, in one volume octavo, with numerous additional notes, and an introductory view of the classification of animals, by one of the ablest and most intelligent of British anatomists, Mr Lawrence of London.

A series of admirable treatises on the Anatomy of the animals included in the Linnean Classes of Mammalia, Birds, Fish, Insects, and Reptiles, will be found under these articles respectively, in Rees's New Cyclopaedia. The four first, we believe, were written by Dr Macartney, and the last by Mr Lawrence. They contain many original observations; and are, at the same time, remarkable, not only for the extent and accuracy of the information which they display, but for the clearness of all their details.

The more important dissertations, on particular subjects relative to Comparative Anatomy, which have been composed of late years by the Continental Anatomists, are recorded in the Mémoires de l'Institut, the Annales du Museum, and the Journal de Physique; those by British authors, chiefly in the Transactions of the Royal and Linnean Societies of London. Among these last, the contributions of Sir Everard Home are deserving of particular notice. The subjects of his investigation have been various and important; and, what is of the utmost consequence, he has accompanied almost all his descriptions with very accurate engravings. The prosecution of scientific pursuits like these, necessarily both laborious and expensive, in the midst of the toils and anxieties of extensive medical practice, evinces a degree of zeal equally rare and meritorious.

Mr Carlisle has lately read to the Royal Society of London, a very interesting memoir on the extravascular parts of animals. The subject is a curious one, and it has been treated in a very able manner by this ingenious author.

(r.)

INDEX.

| Arteries in general | Sect. 30 | |---------------------|---------| | Bone, anatomy of, in general | 156 | | Brain of the adult male | 55 | | —— of the adult female | 79 | | —— before and after maturity | 80 | | Canal, alimentary | 251 | | Cord, spinal, of the adult male | 85 | | —— female | 98 | | —— before and after maturity | 99 | | Ear | 218 | | Embalming | 287 | | Eye | 204 | | Form, external, of the fetus | 3 | | Gland, thyroid | 250 | | Glands, absorbent, in general | 49 | | Hair, anatomy of, in general | 145 | | Heart, of the male adult | 19 | | —— before maturity | 26 | | Inspection of the body after natural death | 273 | | —— after violent death | 283 | | Larynx | 248 | | Liver | 257 | | Lungs | 241 | | Mass, central, of the nervous system | 54 | | Matter, nervous, of the brain | 60 | | —— of the spinal cord | 88 | | Membrane, serous, in general | 165 | | —— synovial | 166 | | Membranes of the brain | 75 | | —— of the spinal cord | 94 | | Mouth | 228 | | Muscle, anatomy of, in general | 125 |

Muscles attached to the skeleton | Sect. 203 | |-----------------------------|---------| | Nerves, plexus and ganglia of | 103, 104 | | —— primary and secondary | 105 | | —— structure of | 107 | | —— classification of | 113 | | Nose | 225 | | Pharynx | 235 | | Placenta | 264 | | Skeleton, in general, of adult male | 169 | | —— female | 188 | | —— before and after maturity | 189 | | —— particular parts of | 202 | | Skin, anatomy of, in general | 131 | | Stature of the male adult | 6 | | —— of the female | 7 | | —— of the fetus | 8 | | Stomach | 252 | | Substance, adipose | 122 | | —— cellular | 118 | | System, circulating | 19 | | —— absorbent | 45 | | —— nervous | 53 | | Systems, common, enumerated | 17 | | Tendon, anatomy of, in general | 161 | | Textures, common, enumerated | 17 | | Trachea | 249 | | Uterus, gravid | 263 | | Veins, in general | 39 | | Vessels, absorbent, in general | 46 | | Weight of adult male and female | 12 | | —— of the fetus | 13 | | —— of child at birth | 14 | | —— of twins | 16 | In the preceding Article, the science which treats of living bodies has been denominated Vital Economy, under which is comprehended the economy of Animals and Vegetables. Each of these departments has farther been stated to embrace two distinct objects of investigation, Anatomy and Physiology. The former alone will occupy our attention in the present Article; the design of which is to exhibit a general view of the structure of plants. To the botanist, it belongs to describe their external forms in such manner as may serve to discriminate species, and assign to each its place in a methodical system of arrangement: It is the province of the anatomist to demonstrate, by dissection, their internal structure, and the construction of their several organs, so as to prepare the way for a rational explanation of their functions.

By reference to the several articles Botany, Plant, Physiology, and Vegetable Physiology, in the body of the work, the reader will meet with many observations and descriptions which relate to the structure of plants. They occur, however, in a form so detached and scattered, are intermixed with so much extraneous matter, and, in their combined result, exhibit so imperfect an account of the subject, that we have found it necessary, in order to afford a juster view of the science in its present state, to recast the whole, and give it in a different, and we trust an improved and more systematic form. To the above mentioned articles we may occasionally refer; but, in the present, it will be our aim to collect and arrange all the more important facts that relate to the structure of plants; and these we shall submit to the reader nearly in the following order.

We shall divide the subject into two Parts; in the first of which we shall treat of the Elementary Organs, of which the Vegetable appears to be principally composed. These organs have been denominated the vascular system and cellular tissue of plants, and under these titles we shall describe, first, the nature and kinds of vessels, and then the nature and kinds of cells by which the tissue is formed. The combination of these elementary organs gives rise to certain textures, which are common to almost every part of the plant, and appear in the well known forms of skin, of bark, of wood, and of pith. On these we shall bestow the appellation of common textures, and exhibit a general view of their structure and disposition in the several parts of the vegetable body. A brief description of some minuter structures, as pores, hairs, and glands, which are also common to many parts of the plant, will conclude this division of the subject.

In the second Part, we shall enter on the consideration of the individual members and more complex organs of the plant. We shall begin with a description of the general structure of Seeds, and afterwards treat more particularly of those bodies under the two great divisions of monocotyledonous, and dicotyledonous seeds, tracing also the changes of form and of structure which they exhibit in their evolution and progress to the state of the mature plant. The structure of the Mature plant itself will next claim our attention; and we shall accordingly exhibit the anatomy of its several members, as of the Trunk, the Branch, and the Root, in their more remarkable varieties and forms. After this, the structure of the organs that spring from these several members, as Buds and Bulbs, Leaves, Flowers, and Fruits, will be separately and distinctly examined; and having thus followed the progressive changes of form and of structure exhibited in the several stages of vegetable existence, we shall terminate our descriptions by anatomical representations of the organs in which the seed was produced, and the series of appearances successively displayed in its formation.

Through the whole of the descriptive detail, we shall adhere as closely as we can to the language of demonstration; supporting and illustrating our representations of anatomical structure by continual reference to figures, selected in great part from authors of repute, and in some instances from dissections made by ourselves. We shall avoid, as much as possible, the introduction of matter of mere reasoning, or even of facts of a physiological nature (proposing to make them the subject of a future article), except in so far as they may be necessary to illustrate anatomical description, and where the better evidence of actual demonstration is not to be obtained. We are aware, that of many reputed anatomical facts very different representations have been given, all equally professing to rest on microscopical observation. In such circumstances, we can do no more than report concisely the statements of different observers; but shall dwell chiefly on those descriptions and representations which seem best entitled to credit, and appear most conformable to the analogies of other organized structures.

When we consider the immense number of species that compose the vegetable kingdom, and call to mind that in form, in size, and in structure, each species differs from every other through every period of its existence, it must appear altogether impracticable to describe and delineate any considerable number. Fortunately, however, these diversities arise not from differences in the elementary organs, but chiefly from their varied proportion, disposition, and texture. In numerous species, the disposition of the internal organs is very similar, where the external form and texture widely differ. In other instances, the arrangement and composition of the internal parts vary not less than that of the external figure. Of these varieties, we shall exhibit different examples; but a more extended and profound view of vegetable organization would, we are persuaded, diminish these apparent anomalies, and break down the limits within which some late writers have attempted to confine the forms of vegetable structure.

In describing individual parts or organs, we might have brought many concurring examples, and exhibited many similar representations, to confirm the views of structure under consideration; but, in general, we have dwelt only on one or two examples, and these we have selected from plants which are either important in themselves, or whose structure has been most satisfactorily displayed, or which seemed to afford the best illustration of the peculiarities we were engaged in describing. From one example clearly given, the reader will readily apprehend the nature of analogous structures, and escape the perplexity and fatigue which unnecessary repetitions might occasion.

Instead, also, of describing the Vegetable at one or two stationary points of its existence, in some of which its size is so minute as to be scarcely capable of demonstration, we have followed it through the several stages of its growth. In this way, we really study it as a living body, continually exerting its vegetative powers, and daily exhibiting the most striking variations in external form, and frequently in internal structure. We hope thus to have conferred an interest on the descriptive part, which may, in some measure, relieve the unavoidable dryness of anatomical details; to have exhibited, in some instances, clearer views of vegetable organization; and to have given a continuity to the subject which isolated dissections, at a few stated periods, could not alone have bestowed. If such displays of the growing structure be thought to partake rather of a physiological character, it may be observed, that we exhibit only the anatomical appearances, without entering at all into the nature or operation of the agents or means by which they are produced.

It remains only to add a few remarks on the nomenclature employed in the present article.

We had wished, as far as we could, to adopt that of Grew and Malpighi, the earliest, and still the best writers on this branch of science. But these eminent authors do not often employ the same terms in their descriptions; sometimes their language is vague; sometimes it rests on false analogies and hypothetical conjectures; and not unfrequently they call the same things by very different names, and use a variety of them. We have, therefore, continued only such of their terms as seemed precise and definite, and which have been sanctioned by subsequent use; but have omitted or rejected others which did not possess these recommendations.

In the description of external parts, we have adhered chiefly to the Linnean nomenclature; but some of the terms employed by Linnaeus, in relation to anatomical structure, are exceedingly vague and inappropriate; others are manifestly erroneous, and, however well suited to the purposes of botany, are not at all to be tolerated in anything that aspires to correct anatomical description.

In the anatomy of seeds, we have adopted many of the terms employed by Gaertner, in his excellent work on the Fruits and Seeds of Plants, most of which had previously been used by Malpighi and Grew.

Thus, in every instance, we have exercised our own judgment in the selection of terms, and, where it seemed necessary, have subjoined the synonyms of different writers. Though we presume not to say that we have uniformly chosen the best, we trust they will always clearly express the idea we designed to convey; and that, in general, they have been used in one and the same sense, and in no other. Except in one or two trivial instances, we have not ventured to introduce new terms, but have studiously sought to avoid it, retaining even an inappropriate expression, sanctioned by use, if it did not, at the same time, lead to ambiguity, or convey an idea evidently false; and we have, in general, resisted that torrent of new and barbarous terms, founded often on fancied refinements and pretended discoveries, with which several Continental writers have of late attempted to deluge this branch of science.

PART I.

OF THE ANATOMY IN GENERAL OF THE ELEMENTARY ORGANS AND COMMON TEXTURES OF VEGETABLES.

CHAP. I.

OF THE ELEMENTARY ORGANS.

1. Before we proceed to describe the structure of the individual parts of vegetables, it may be useful to exhibit a general view of the elementary organs of which they seem to be composed. Such a view will prepare the reader for understanding more clearly the descriptive language hereafter to be employed, and will even much abridge the extent to which that description must otherwise be carried.

2. Every one is familiar with the natural division of plants into herbs and trees, and is aware that how differentsoever they may appear in form and texture, they all possess, in common, certain parts or members which we name the root, the trunk, and the branches, from which proceed the leaves, the flowers, the fruits, and seeds. Infinitely varied as these several parts are, in figure, size, and texture, they all originate from a few constituent or elementary organs, whose situation, proportions, and combination, give rise to all the diversity that we see.

"Upon the anatomical analysis of all the parts of a plant," says Grew, "I have certainly found, that, in all plants, there are two, and only two, organical parts essentially distinct, viz. the pithy part, and the ligneous part." (Anatomy of Plants, p. 19.) "And as every part hath two, so the whole vegetable, taken together," he adds, "is a composition of two only, and no more. All properly woody parts, strings, and fibres, are one body; all simple barks, piths, parenchymas, and pulps, and, as to their substantial nature, peels and skins, are all likewise but one body; the several parts of a vegetable differing from each other only by the various proportions and mixtures, and variated pores and structure of these two bodies." (Ibid. p. 47.) In the anatomical descriptions of Malpighi, the compound structure is resolved, in like manner, into two constituent parts, called by him the ligneous and utricular portions. To these parts may be assigned the general appellations of the Vascular System and Cellular Tissue of plants, the description of which shall form the first subjects of consideration.

SECTION I. Of the Vascular System.

ARTICLE I. General Characters of the Vessels.

5. By the vascular system may be understood, in a general sense, all those parts of a plant which do not exhibit the form either of membrane or of cells. It constitutes almost the entire bulk of the more solid parts of trees; and, by Grew and Malpighi, was denominated the ligneous body, in contradistinction to the cellular tissue which accompanies it, and which forms by far the largest portion of many herbaceous plants. To common observation, a piece of dry wood appears to be a mass of solid fibres, that is, a series of particles arranged in a filiform figure, and destitute of any continuous canal. Thus Tournefort and others, considered the ligneous parts of a plant to be a mass of minute solid filaments, placed parallel to each other, like the threads in a skein of silk, between the interstices of which the sap ascended; but the anatomical researches of Grew conducted him to a different conclusion. "If it be asked," says he, "what all that part of a plant, whether herb or tree, which is properly called the woody part, what all that is? I suppose that it is nothing else but a cluster of innumerable and most extraordinary small vessels or concave fibres." (Anat. of Plants, p. 20.) Malpighi held similar opinions concerning the vascularity of plants, which was farther attested by the microscopical observations of Hooke and Leuwenhoeck. Du Hamel, though he admits that, under maceration, the parts of plants seem capable of indefinite subdivision, yet, from many circumstances, avows his conviction of their vascularity; and Hedwig maintains that the oldest and most compact plant is but a congeries of vessels and cells, which have nothing of the character of a fibrous solid, except in the thin membranous coats by which they are formed. (De Fibre Vegetab. Ortu, p. 17.)

4. Few circumstances have contributed more to perplex and retard our knowledge of the structure of plants, than the vague and erroneous nomenclature that has been employed to designate their constituent organs, more particularly in relation to the vascular system. Thus the several terms filaments, fibres, strings, threads, and nerves, which, in their ordinary acceptation, are understood to express a solid substance, have been constantly made use of in describing the tubes or vessels of plants. The same organs, however, even by the same writers, are frequently called tubular bodies, ligneous tubes, concave fibres, ducts, canals, arteries, veins, and vessels. In our future descriptions, we shall employ the term vessel in a generic sense, to express all the diversity of names just enumerated, and the different kinds or species of vessels we shall hereafter attempt to discriminate by appropriate appellations.

5. Vessels, as we have said, exist in almost every part of a plant. In the higher orders of animals the fluids contained in the vessels are conveyed to a central reservoir called the heart, from which they are again sent out to all parts of the body. Near to this reservoir, the vessels are few in number and large in size; and they gradually lessen in size and increase in number as they recede from it. In plants, there is no such reservoir, but the fluids which enter by innumerable mouths at the root, are at once distributed equally through all parts of the vegetable that are fitted to receive them. Hence in plants, there is little variation in the diameter of the vessels; and their general figure is therefore cylindrical.

6. From the extreme minuteness of the vessels, it is scarcely possible to compute their number with accuracy. By driving off their fluids without destroying their figure, as is done in the preparation of charcoal, Hooke numbered in a line, 1/8th part of an inch long, not fewer than 150 vessels; therefore, in a line an inch long, there must be 2700, and in a surface of a square inch, 7,290,000 vessels, "which would seem incredible," says he, "were not every one left to believe his own eyes." These facts he verified by other observations on decayed wood, in which the vessels were empty, and also on petrifactions of ligneous bodies, in which the places of the vessels were very conspicuous. In very close and dense wood, as that of Guiaicum, the vessels were still more minute than in the examples just quoted. (Micrographia, p. 101, 108.) In a piece of Oak of the size of about 1/8th part of a square inch, Leuwenhoeck reckoned 20,000 vessels; so that in an Oak-tree of no more than one foot in circumference, or about four inches in diameter, there will be found, according to his computation, 200,000,000 of such vessels. (Select Works, translated by Hoole, Vol. I. p. 3.) The largest vessel observed by Hedwig (De Vegetab. Ortu, p. 26,) in the stem of the Gourd, appeared through his microscope about 1/8th of an inch in diameter; and as his instrument magnified 290 times, the true diameter must be reckoned the 3480th part of an inch, which would give for the square inch 12,110,400 vessels. In certain plants, however, the vessels are large enough to be discerned by the naked eye, and in some cases acquire a large size.

7. The vessels of plants do not, like those of animals, exist single, but are collected into fasciculi or cell bundles, which, however, have often the appearance of single vessels. In the stems of herbs, and in roots, Grew discovered each small fasciculus to be composed of from 30 to 100, or sometimes many hundred vessels. (Anatomy of Plants, p. 20.) The direction of these fasciculi in the trunk is generally perpendicular, but in other parts their course is often oblique, and in their smaller ramifications they produce all sorts of figures. In herbs, the fasciculi are more or less numerous, and placed often at considerable distances from each other, exhibiting the appearance of small columns dispersed through the cellular tissue; in other instances, they are much more numerous, but destitute of any symmetrical arrangement; while, in trees, they are disposed regularly around the axis, presenting in their transverse section, the well known appearance of concentric circles in the wood.

8. In some parts, where the fasciculi stand at a distance from each other, some vessels often quit one

VEGETABLE.

10. Another general circumstance in the vessels of Elementary plants, is, that we do not discover in them any structure which has the true nature and use of valves, similar to what is met with in the veins and absorbent vessels of animals. Dr Hooke could never observe in their canal anything that had the appearance of valves. (Micrographia, p. 116.) Did such a structure exist, the absorption of nutrient matter from the lobes of the seed, and its conveyance, in a backward course, to the embryo, could not, says Grew, have place; neither could the root, as it often does, grow upward and downward both at once. (Anatomy of Plants.) If the piece of a root of elm-tree be cut in autumn, the juices, says Du Hamel, are found to escape indifferently at either end, as the one or the other is alternately held downward; a circumstance, he observes, inconsistent with the opinion of Mariotte, who maintained the existence of valves. (Phys. des Arbres, Tom. I. p. 56.) It is well known also, that many plants may be made to grow in an inverted position, so as to put forth leaves and flowers from their roots; and large trees have been nourished by juices received through the extremities of their engrafted branches, after all connection between the earth and the roots had been cut off. In general, indeed, the extreme minuteness of the vessels seems almost to preclude the possible existence of valves in their canal: but in some instances, where the vessels in aged trees have become enlarged, membranous productions have been found to occupy their cavities, which some have alleged to perform the office of valves. They occur, however, only at an advanced period of growth, and form no necessary part of the structure of the vessel; and, instead of promoting, contribute only to obstruct the course of the fluids. It was the opinion of Malpighi that the frequent junctions which the fasciculi of vessels make with each other in their ramifications, might be considered to bestow on them a sort of valvular function: but, in most instances, these fasciculi run parallel without forming ramifications, and no such valvular function can then be considered to have place.

Thus far with regard to the general nature of the vessels of plants: let us next discriminate their several species or kinds.

ARTICLE II.

Of the Common Sap-Vessels.

11. To ascertain the nature and situation of the Sap-Vessels vessels of plants, various means have been employed. The plant has been dissected both in its dry and recent state; the natural qualities and movements of its fluids have been observed, and its vessels have been filled with coloured liquor, by causing it to vegetate in them. By the combined use of these several means, many important particulars have been ascertained; but it must be acknowledged, that the question is still beset with doubts and difficulties, and that, with relation to it, great diversity of opinion continues to prevail. A concise statement of the facts ascertained, with respect to the movements of the vegetable fluids, may perhaps serve best to define the situation and kinds of the vessels that convey them.

12. It has been proved that, early in spring Elementary before the leaves appear, a watery fluid rises abundantly in the woody part of the trunk of trees, and continues visibly to ascend to the very extremity of the branches, until the leaves are developed; when, to appearance, it ceases to flow, and can no longer be collected by perforating or tapping the tree. This fluid has been shewn to ascend through the wood, and to rise, in general, most abundantly through its youngest or outmost circle: but in trees, whose vessels have not been obstructed from age or other causes, it rises through every circle to the very pith, and, as far as can be judged, in all the vessels that compose those circles. At this early period of vegetation no fluid is found in the bark; nor between it and the wood; nor in the pith: but the vessels of the bark are perfectly dry. These facts are deducible from observations on the natural flow of the fluids by Grew, Du Hannel, Walker, and others; and are supported by various experiments of M. De la Baisse, Bonnet, Reichel, and others, made by causing plants and parts of plants to grow in coloured liquors, in which the vessels of the wood alone became filled, but no tinge of colour was communicated to those of the bark. To these vessels the several names of lympheducts, sap-vessels, ligneous tubes, ascending and adducent vessels, have been applied:—we shall in future denominate them sap-vessels.

13. The vessels, which thus form the mass of Sap-Vessels wood, have by some writers been distributed into different kinds, and supposed to exercise very different functions. At certain periods of vegetation they appear empty; and hence Malpighi supposed two species of vessels to exist in the wood, one destined to carry sap, and the other to convey air; and to these latter, from their supposed office, he gave the name of tracheæ, and from their structure called spiral vessels. (Anatom. Plantar. Idea, p. 3.) Grew also believed these empty tubes to be air-vessels, but admitted that, at certain seasons, they carried sap. At an early period, however, Ray maintained that the vessels, thus supposed to convey air, were truly sap-vessels; and Du Hannel, in common with Grew, admitted that they carried sap in spring. Hill considered them altogether as sap-vessels, and Reichel, Hedwig, and others, by experiments with coloured fluids, proved that such was their true office. On the other hand, no experiments, says Ludwig, have yet shewn that there exist in vegetables, vessels destined to convey only air: and in this opinion, subsequent writers, with the exception of M. Kieser, have very generally acquiesced. We may therefore reject altogether the existence of air-vessels or tracheæ in vegetables; and consider all the vessels of the wood, by whatever name they may be called, as destined to carry sap. It will, however, be convenient to treat of their general nature and form under the distinct appellations of sap-vessels and spiral vessels, by which they are commonly known.

14. By Grew and Malpighi the common sap-vessels were regarded as entire tubes, having no apertures but in their direction of the length. The former represents a single vessel as having the appearance exhibited in fig. 1. Plate XV., the aperture or canal of which is not visible, unless highly magnified, as in fig. 2. According to Malpighi, these vessels send off numerous capillary filaments to the cellular tissue, so that the cells are surrounded by a plexus of vessels, as is particularly seen in the pith of Elder and some others; and these ramifications, he adds, spring probably from the perpendicular vessels both in the bark and wood. (Anatom. Plantar. p. 29. Lugg. Bat. An. 1688.) These lateral ramifications were observed also by Leuwenhoeck in a piece of fir-wood, newly leaved. Of this wood, he procured a longitudinal section so extremely thin, that he could see distinctly the particles of fluid moving in the vessels, as represented in the upper portion of fig. 3. Plate XV.; while lower down, on many parts of these vessels, small points or dots were visible, which he at length discovered to be round apertures: and as he did not see these apertures in any other parts than those in which he had separated the horizontal cellular tissue from the perpendicular vessels, he concluded that, at these points, these two organs were connected. He farther separated two of the vessels from the remainder, and through the microscope they appeared as in fig. 4: but the "engraver," he adds, "said that he could not possibly draw all the jagged parts that he saw, and we both of us perceived, in the broken membrane or coat of the tube, many excessively minute vessels, which, by reason of their smallness, he was unable to express in the drawing." (Select Works of Leuwenhoeck, by Hoole, Vol. I. p. 12.) These opinions concerning a direct communication between the vessels and cells of plants, receive countenance from the experiments of De La Baisse and Reichel with coloured liquors; both of whom observed, in some instances, a tint of colour to be communicated from the vessels to the adjacent cells.

15. It may however be said, that this communication between the vessels and cells, is maintained not by ramifications from the vessels, but through apertures or pores in their sides: and, accordingly, many appearances have been remarked as existing on the sides of the vessels, of which different authors have given very different representations, and which some have regarded as pores. Thus, on the vessels of the Fir, Malpighi observed certain dotted appearances, which he describes as roundish tubercles, and which were so numerous that they appeared to cover the vessels. On the vessels of the Elm, the Beech, and the Willow, Leuwenhoeck saw similar particles which resembled small globules. (Select Works, Vol. II. p. 1.) Dr Hill, one of those conceited writers who of late profess to study only nature herself, and affect an entire disregard of the labours of their predecessors, describes the vessels of the albumen, or newly formed wood of the Willow, as connected with each other by a flocculent interstitial matter. When, by long maceration, this matter is detached, the vessels then exhibit a dotted appearance; and, if examined by a highly magnifying power, these dots, according to him, are so many oval swellings, and each has, as it were, a mouth. Through these mouths, which he represents as innumerable, and existing on all parts of the vessels, he conceives the fluids to be discharged into the cellular tissue (On the Construction of Timber, p. 18.) but he has omitted to show that the cells of the tissue possess any corresponding mouths to receive them. In fig. 5. Plate XV. is a repre- sentation of these vessels connected by flocculent matter, with their extremities collapsed from the escape of their juices, and their sides sprinkled with the little mouths which he mentions. These mouths, if they exist at all, are probably not pores in the sides of the vessels, but the little apertures seen by Leuwenhoek, and produced by the separation of the cellular tissue, while the parts are still young and tender. The same author, speaking of the vessels of the mature wood of the Pear, states them to be close canals, as in fig. 6, with no lateral apertures in them.

16. A still later writer, following closely in the track of Hill, and who sets out with observing, that "the microscopical organization of plants is but little known, and that it is in vain to look for the true principles of the science in the works of Malpighi and Grew," declares, that not fewer than five species of vessels are to be found in the woody part of plants: These he denominates porous tubes, cleft tubes, tracheae, mixed tubes, and vessels en chapelet, from their supposed resemblance to a string of beads. Of these several species, we have given representations in figures 7, 8, 9, 10, 11, and 12, Plate XV. The first species, or porous tubes, according to this writer, exist in every part of the plant, where the sap moves with freedom. Their sides are covered with small eminences or projections, in the centre of which is to be found a small pore. (Exposition de la Théorie de l'Organisation Végétale, p. 107.) Improving a little on Hill, he represents these pores not as promiscuously placed, but as ranged in transverse lines (fig. 7); and through them he conceives the fluids of the plant to percolate; not however into the cells only, but out of one layer of tubes into another, in a lateral direction. In this manner, he conducts the fluids from the centre to the circumference of the wood, and at length, by a route not so easily followed, contrives to get them into the vessels of the bark, the sides of which he declares to be perfectly entire, and alike destitute of pores and clefts. (Ibid. p. 297.) Of such physiological notions it may truly be said, that they are every way worthy of the fantastical anatomy on which they appear to be founded.

17. Several German writers have attempted to verify the observations of M. Mirbel in regard to the existence of these pores. They all differ from one another, and, as might have been expected, are all at variance with M. Mirbel. Bernhardi, following Malpighi, deems the alleged pores to be elevations on the surface of the vessels; Rudolphi represents them as vesicles attached to their sides; Link regards them as globules contained within the vessels; and Kieser, as we shall afterwards see, knows not what to make of them. These very different opinions, formed on viewing the same objects, sufficiently manifest the difficulty and uncertainty of microscopical observations made with highly magnifying powers. The causes of this uncertainty were long ago pointed out by an experienced and most sagacious observer,—the first who employed the microscope in the examination of the structure of plants. His statement may perhaps account for, though it should fail to reconcile, the differences in question. "Of such minute objects," says Dr Hooke, "there is much more difficulty to discover the true shape by an instrument than of those visible to the naked eye; the same object quite differing in one position to the light, from what it really is, and may be discovered to be, in another: and therefore I never began to make any draughts, before, by many examinations in several lights, and in several positions to those lights, I had discovered the true form: For it is exceedingly difficult in some objects to distinguish between a promineney and a depression; between a shadow and a black stain, or a reflection and a whiteness in the colour. Besides, the transparency of most objects renders them yet much more difficult than if they were opaque. The eyes of a fly, in one kind of light, appear almost like a lattice drilled through with abundance of small holes; in the sunshine they look like a surface covered with golden nails; in another posture, like a surface covered with pyramids; in another, with cones; and in other postures of quite other shapes." (Micrographia, Preface.)

ARTICLE III.

Of the Spiral Vessels.

18. Various as have been the opinions of writers respecting the common sap-vessels of plants, they have differed yet more in their views concerning the position, number, size, structure, and uses of those which have been denominated spiral. The common fathers of Vegetable Anatomy, Grew and Malpighi, who, at the same time, but in different countries, prosecuted their inquiries, for many years, without any knowledge of or communication with each other, are nearly of one opinion on all the more important points in relation to these vessels. Later writers have differed alike from them, and from each other, on almost every point. As the subject is of fundamental importance in the economy of vegetables, we shall endeavour, at the risk even of a little extension of our plan, to set before the reader the leading facts and opinions concerning it; to canvass their relative merits; and deduce from the whole such conclusions as seem most nearly to approach the truth.

19. Malpighi describes spiral vessels as existing in Opinion of the ligneous parts of all plants. He called them Malpighi; spiral tubes, because, when extended, they were resolved, not into separate rings, but into a single zone, which might be drawn out to a great length. In general, they form continuous tubes, but are sometimes contracted at regular distances, so as to resemble somewhat a series of oblong cells. One of these contracted spiral vessels is represented in fig. 14, Plate XV. at the extremity of which, the spiral filament is in part drawn out, and similar appearances of the spiral structure are exhibited in figures 9 and 10. by Mirbel. In herbs, according to Malpighi, these spiral vessels constantly accompany the common sap-vessels, and are ensheathed by them; in shrubs, they occur in every part of the wood, single or in clusters; and in trees, an intermixture of spiral vessels with the common sap-vessels, is observed in every part of the wood. In the Fir, they are found immediately beneath the bark, and are so numerous as to constitute the chief bulk of the wood. They exist with the sap-vessels in the petioles and ribs of the leaf, and likewise in the petals of the flower. In Elementary the roots, they are also met with, and in some roots Organs are so abundant, as to exceed in bulk all the other parts. They exist, he adds, in every part of the plant except the bark; and are annually formed with the albuminous vessels of trees. (Anatom. Plantar. passim.)

20. From the writings of Grew we collect also, that spiral vessels exist in every part of a plant, except the bark. In the root they are numerous, of very various size, and their bore is generally larger than that of the common sap-vessels. In the trunks, both of herbs and trees, they are equally visible; and in position, size, and number, subject to great variation. Sometimes they are collected into fasciculi; at other times they are disposed in rays; and in other instances they are arranged in a circular form: They stand sometimes next to the pith, in other instances next to the bark; and in other cases again, they alternate with the common sap-vessels in every part of the wood. They have a more ample bore than the common vessels, and vary in size to at least twenty different degrees. In the leaf, they always accompany the sap-vessels; and both in its petiole and ribs, are constantly surrounded or ensheathed by them. They have a similar position in the petals of the flower, and in the vascular parts of the fruit. (Anatomy of Plants, passim.) Hence, then, it appears, from the dissections of Malpighi and Grew, that, in every plant in which vessels are to be seen, and almost in every part of it, spiral vessels abound; they exist, however, only in the ligneous portion, or that part in which the sap ascends, and are never to be found in the bark.

21. By Du Hamel, the spiral vessels, supposed to convey air, are described as existing in the leaves and the flowers, the petals of which are almost wholly composed of them. In the herbaceous portion of young branches, they are also well seen; which portion afterwards becomes ligneous; so that it cannot be doubted that they exist in the wood, though he could never discover them but in young branches. (Phys. des Arbres, Tom. I. p. 42.) If, however, all the empty vessels, seen in a transverse section of the wood, be deemed air-vessels, and all air-vessels have a spiral structure, then, says this author, they would, in many plants, form a great part of the ligneous body. From these large vessels, however, he has seen, in autumn, fluids to escape; so that they are not properly air-vessels, or, as Grew observed, they sometimes carry sap. They are not to be found in the bark.

22. Under the common name of sap-vessels, Hill delineates all the varieties of vessels that constitute the wood; they are largest in the outer circles, smaller in the others; they contain, says he, in spring and at midsummer, a limpid liquor; but at all other seasons they appear empty, and have therefore been erroneously deemed air-vessels. He says nothing of their spiral construction; but describes the vessels, which form the chief mass of the wood, as possessing solid and firm coats, forming an arrangement of plain and simple tubes; as in fig. 6. Plate XV.; resembling those of the albumen, except that they have no mouths in their sides. (On the Construction of Timber, p. 8 & 19.) But though, with Du Hamel, he was unable to trace their spiral structure in the wood, yet there can be no doubt of their existence in that part; which, as we shall afterwards show, has been recently demonstrated by Kieser.

23. M. Reichel maintains their existence in all parts of the plant. By causing plants to vegetate in coloured fluids, he traced them from the roots, through the trunk and branches, to the extremity of the leaves, and into all parts of the flower,—as the calyx, the petals, the style, the stamens, and the anthers. In fruits and in seeds, and in the radicle and plume of the latter, they were equally apparent. The coloured liquors, as they rose, communicated a tinge to the cellular tissue of the wood, as was previously observed by De la Baisse; but no trace of colour was ever observed either in the bark or pith, which therefore contains no spiral vessels. He considered the spiral vessels as the organs everywhere conveying nutrient matter to the plant, and as having no title to the appellation of air-vessels. (Encyclop. Méthodique, Article Physiol. Végét. p. 288.) Similar experiments of Hedwig and others, confirm these facts as to the universal distribution of the spiral vessels, and their bearing to every part the fluids absorbed by the roots. In his late work, M. Kieser, as we shall afterwards see, in describing the vascular system of the ligneous parts of plants, regards it as composed entirely of spiral vessels, and asserts their existence in every part of the plant except the bark and pith.

24. Against these combined authorities M. Mirbel opposes his fanciful views. We have already enumerated the five different species of vessels which he regards as constituting the woody part of plants. According to him, true spiral vessels (which he continues to denominate tracheae) are not to be found in the root, but only in the trunk and the parts which are produced from it. Even in the trunk, they are to be found only around the pith, and never in the exterior ligneous layers. He admits that they exist in all soft and succulent parts, and that coloured fluids rise in them as well as in the other varieties of vessels; but they never are to be found either in the bark or pith. (Exposition de la Théorie de l'Organisation Végétale, p. 74, 78.) It appears, therefore, that the vessels which are thus erroneously called tracheae, are destined to carry fluids; and as to the parts in which they do or do not occur, the opinion of M. Mirbel weighs as nothing with us, in opposition to the facts observed by so many preceding and subsequent writers.

25. From the combined observations, therefore, of all the preceding writers, with the exception of M. Mirbel, we collect that the vessels heretofore called air-vessels and tracheae, and which possess a spiral conformation, exist together with those called common sap-vessels, in every part and organ of the plant, except the bark. It appears also, that, though they are often found empty, yet their true office is to carry sap. This may be concluded not only from the actual occurrence of sap in them early in spring and again in autumn, and from the entrance of coloured fluids at all seasons; but from the circumstance that, in some parts, no other vessels appear to exist by Elementary which the rising sap can be conveyed. Are we, therefore, with many, to consider them, from the period of their formation, as a species distinct from the common sap-vessels, or are both to be held merely as varieties of one common kind?

26. It is allowed, on all hands, that spiral vessels are most readily visible, and are most numerous in the tender and succulent parts of vegetables, in which they form almost the entire bulk of the vascular portion. In the albuminous part of trees, which is added annually to the pre-existing wood, they are not so readily seen. Even in trees, however, while still succulent, the first circle of vessels formed, contains spiral vessels; as Du Hamel observes, and even Mirbel admits; but, at a later period of vegetable growth, the whole of the vessels, formed annually in trees, are represented by Grew as common vessels, which, he adds, "begin to be formed in spring; but the spiral vessels not till the latter end of summer, or thereabouts, at least not till about that time do they appear." (Anatomy of Plants, p. 131.) Malpighi also describes these spiral vessels as gradually appearing in the albumen, and continually augmenting in size in every successive ring of wood. A similar remark, as to increase of size, is made by Grew: "the spiral vessels," says he, "being amplified in each annual ring, at least for a certain number of years, so as to form a vessel of a wider bore:" (Anatomy of Plants, p. 139.) and accordingly, in all the plates of both these writers, and in those of other authors, the spiral vessels are always represented of different sizes in every part of the wood.

27. From the foregoing facts, it would seem, that, in the young and succulent parts of plants, the spiral construction of the vessels is almost, if not actually, coeval with their existence; but that, in more rigid textures, they are not so early formed, or at least are not discoverable in parts in which they are subsequently seen. Hence, therefore, we must suppose a sort of transformation to occur with respect to these vessels, or, to use the language of Grew, that they "are post-nate, and seem produced by some alteration in the quality, position, and texture of their fibres." If, indeed, spiral vessels exist in every part of the wood, but are not for some time visible in the albumen, and if the albumen be, as it most certainly is, the substance by which the ligneous layers are successively formed, then it follows, that the occurrence of spirals in the wood must be the result of some change induced on the vessels that at first constituted the albumen. Hedwig, indeed, considered all the albuminous vessels to possess from the first a spiral conformation, and that they gradually acquired the characters they possess in the wood. We shall presently see that the researches of Kieser support the same view, and thus go to establish the doctrine of transformation, first announced by Grew. Mirbel, however, protests against the transformation of one variety of vessel into another, and maintains that each of the five species, which he enumerates, retains, without change, its original character and form. He nevertheless describes his fourth species, or what he calls mixed tubes, (fig. 10.) as composed of the three preceding species; and "such," he adds, "is the simplicity of vegetable organization, that frequently one and the same tube exhibits (as in fig. 12.) all the several species combined." (Expos. de la Théorie, &c. p. 78, 80.) That the same vessel, from the operation of local causes, should sometimes exhibit, in different parts, a variety of appearance and form, is perfectly consistent with the principle of change and transformation which has been supposed to have place; but that nature should from the first combine in one vessel, unsusceptible of future change, five different species of forms, is not quite so credible; and to ordinary minds would certainly afford no proof of the "simplicity" of her operations.

28. If then we adopt the opinion, that in young and succulent parts the vessels which carry sap have a variety of Sap-Vessels from the first a spiral construction; and if, as seems to be proved by the dissections of Grew, of Hedwig, and of Kieser, no other vessels, destined to such an office are, frequently, to be found, then we must conclude that, in such parts, only one species of sap-vessels exists, to which, from the first, the spiral construction belongs. If, on the other hand, it appear that, in the more rigid texture of the albumen of trees, no spiral vessels are at first to be found, but that they afterwards become visible in the wood, then it follows, from what has been already stated, that the spiral vessels of the wood are produced from the common sap-vessels of the albumen, and are consequently to be regarded, not as an original species, but only as a variety of one common kind. That such probably is the fact, will farther appear from the account afterwards to be given of the structure of these vessels, and of the actual transformations which they seem to undergo. Even those who may still be of opinion, that a difference in external form warrants a nominal distinction of species, must, we think, admit that, in office, no ground for such distinction exists; but that all the vessels in the ligneous parts of plants are destined to exercise one and the same function. In relation to the economy of vegetables, this is a fact of far greater importance than any opinions that may be formed regarding the varieties of appearance or structure in the vessels themselves.

Article IV.

Of the Structure of the Sap and Spiral Vessels.

29. We have next to offer a few remarks on the structure of the vessels we have been engaged in describing. On this head, we shall not go much into detail. When we have seen such difficulties attending the correct observation of them in their entire forms, it may fairly be presumed that still greater perplexity must accompany the investigation of their constituent parts. What, therefore, we have to advance, may be regarded rather as matter of opinion than of fact; and, in the present state of the science, this point must be deemed more a subject of curiosity than of use.

30. According to Malpighi, the common sap-ves- sels of the wood, when viewed longitudinally, appear to be formed of a series of small vesicles or cells mutually opening into each other. These cells possess different forms, but in some vessels there seems to be no trace of such a cellular structure. In the Elementary Oak, the cells are represented to possess a roundish figure, and in the Vine they possess an oblong form; as in Plate XV. fig. 13. (Anat. Plantar. Idea, p.2—24.) In these, and similar instances, Malpighi seems either to have mistaken a series of elongated cells for vessels, or to have conceived that the contractions, occasionally formed in the vessels of certain plants, afforded evidence of their being constructed originally from cells. It is certain that, in the vessels of most parts of plants, no such cellular construction is apparent.

31. Grew, on the other hand, considered the common sap-vessels to be composed of strait fibres, or rather smaller vessels, placed parallel to each other, and set round so as to form a cylindrical tube. (Anatomy of Plants, p.112.) In the opinion of Leuwenhoeck, the vessels are composed of two fine transparent coats, formed of other vessels exceedingly minute, which are disposed partly in a longitudinal, and partly in a circular direction. (Select Works, by Hoole, Vol. I. p. 11.) Du Hamel attempted to gain a knowledge of their structure, by submitting them to long maceration. By this method, he separated the ligneous layers into leaflets thinner than the finest paper, and the fasciculi of fibres or vessels that composed these layers, were farther separated into minuter filaments, placed parallel to one another, like the threads in a skein; and these filaments again seemed capable of almost indefinite subdivision. (Phys. des Arbres, Tom. I. p. 31.) Hill considered the vessels of the albumen to be formed of the same matter as the cells. He describes them as at first very delicate, and to collapse when emptied of their fluids. Sometimes the coat of which they were formed resembled a thin parchment, in which traces of lines surrounding one another were visible, so that the coat seemed as if composed of several membranes that were vascular. In one instance, where a strong light was made to penetrate the vessel, it appeared as if composed of numerous cells; but, on farther examination, these seeming divisions altered their places, and were found to proceed from small portions of watery sap still retained in the vessel. This appearance, as he properly observes, may be a very necessary lesson against hasty judgments. (Construction of Timber, p. 33.)

32. M. Mirbel's opinion concerning the formation of vessels may next be shortly noticed. He sets out with asserting, that "the entire mass of the plant is nothing but cellular tissue, the cells of which differ only in form and dimensions." This he declares to be the basis of his theory; and he may perhaps be right in thinking, that "no one, before himself, had formed a similar conception of vegetable organization." The cells and vessels of this tissue are farther considered to be produced out of one and the same membranous tissue. In forming cells, this membrane is supposed to dilate in every direction; in producing vessels, it increases only in length. (Exposé de la Théorie de l'Organisation Vég., p.9—103.) Of the structure of this primitive membrane itself, he professes to give no information; and his account of the manner in which the vessels are produced out of it, is so entirely mechanical, so clumsily conceived, and so incapable of execution, that we deem it altogether unworthy of the attention of any one accustomed to contemplate the structure and formation of organized textures.

33. Concerning the structure of the spiral vessels, opinions have varied still more than in relation to those just considered. Malpighi describes them as composed of a thin zone, formed of a pellucid silvery plate, somewhat broad, which, being placed spirally, and united at its edges, constructs a tube, interiorly and exteriorly, somewhat rough. When this tube is drawn out, it does not separate into distinct rings, but is resolved into a continuous spiral zone. At particular places, these vessels are sometimes contracted, so as to exhibit the appearance of oblong cells opening into each other, as in fig. 14 Pl. XV. In size they greatly surpass the ordinary sap-vessels; and their canal is then frequently occupied by membranous vesicles, which nearly fill their cavity. (Anat. Plantar. p. 3—26.) These vesicles were also observed by Leuwenhoeck, and their appearance, both in the transverse and longitudinal section of an enlarged vessel, are represented in fig. 15.

34. According to Grew, the thin plate that forms the spiral vessel, is not always of the same breadth, and, instead of being flat, it has sometimes the form of a round thread. When minutely examined, the spiral zone, he adds, is never one single piece, but consists of two or more round filaments placed collaterally, but perfectly distinct. These component filaments he regards as united by other smaller transverse filaments, and the thin plates which they form by their connection, constitute the spiral vessel; "as if we should imagine," he adds, "a piece of fine narrow ribbon to be wound spirally, and edge to edge, round a stick, and the stick being drawn out, the ribbon to be left in the figure of a tube, answerable to a spiral vessel." As, however, the ribbon is composed of numerous threads, placed parallel to each other, so is the plate that forms the spiral vessel; and it is according to the greater or less delicacy of the vessel examined, and the manner of its dissection, that it appears to be constituted either of a flat plate, or a round filament. The spiration of the filaments he considered to be made in the root, from right to left, and in the trunk, from left to right. (Anat. of Plants, p. 73, and 117.)

35. The opinion of Du Hamel, with respect to the construction of these vessels, was very similar to that of Grew, and he employed the same analogy of a ribbon twisted round a stick, to illustrate it. Hedwig gave a very different account of them. He of Hedwig considered the spiral vessel to be composed of two distinct parts; one a membranous canal conveying air, and the other a spiral tube rolled round it, by which the fluids were conveyed. The spires of the tube, in some instances, are represented as close; in others, they are separated, and the intervening portions of the membranous canal exhibit a dotted appearance. He considered all the sap-vessels, from their first formation, to possess this compound structure, and, by a series of changes, which he professes to describe, to be ultimately transformed into the solid fibre of the wood. (De Fibrae Vegetab. Ortu; p. 25.) Others, also, have believed the spiral vessel to be formed of a membranous tube, but have denied that it

VEGETABLE.

Elementary conveyed air, and the spiral tube of Hedwig they have regarded as a solid plate or filament. From the different appearances which they exhibit, M. Treviranus and Bernhardi distinguish several varieties of spiral vessels, as does also M. Kieser, whose account of these vessels is not only the latest and most elaborate, but that probably which approaches nearest to truth. We shall, therefore, subjoin a brief abstract of his observations on the situation and structure of these vessels, and more particularly on the series of transformations which they seem to undergo.

According to M. Kieser (Mém. sur l'Organisation des Plantes, p. 115, à Harlem, 1814), spiral vessels are found in all the more perfect plants, from the earliest period of their existence, and in all parts of them except the bark and pith. In herbs, they are collected into fasciculi of thirty or more vessels; in trees they constitute the wood, and are annually augmented in number by a new layer. In different plants, and even in different parts of the same plant, they vary much in size, being generally largest in succulent plants, especially those of rapid growth; and in such plants, they continually augment in size. In some woods, they are extremely small; in others, much larger. In aged plants, both in the root and trunk, they are at length more or less completely obstructed by a species of membranous vesicles, previously observed by Malpighi and Leuwenhoek, which originate from the sides of the vessels. Nothing but air is commonly found in their cavity; but in the wood of Guaiacum, he has seen all the spiral vessels entirely filled with resinous matter, and the whole cellular tissue completely filled with the same matter. He does not know what anatomical relation subsists between the spiral vessels and the other organs; but thinks there is no direct communication between them and the cells.

The construction of these vessels M. Kieser professes to have studied with the greatest care, and to have established incontestably the following points. Sometimes, says he, only one fibre, sometimes many, go to form the spire of a vessel. These fibres are commonly round, sometimes a little flattened, and are twisted spirally about an empty space, so as to form a tube. The spiral fibres in young plants, and sometimes in mature ones, are in close contact; in other instances they are separated, and the interstices are then occupied by a dotted or punctuated membrane, as is very frequent in trees; or sometimes they are connected by ramifications which proceed from the spiral fibres themselves. From the minuteness of the spiral fibre, it is difficult to decide whether it is a solid or tubular body, and often, from the same cause, to pronounce whether it is round or flattened. It is transparent; has considerable consistence and tensility; and, in some plants, appears to possess elasticity.

The number of fibres that form the spire of a vessel is very various; sometimes, as before remarked, there is only one, but more often several, which are twisted in the same plane, and the same direction. He has seen nine fibres thus united, and when unrolled, the spires of the vessel then seem to form a kind of ribband. When many fibres are employed to form a spire, they always run parallel, and do not cross; so that the side of the vessel has never more than the thickness of a single fibre. At their first formation, the fibres are not united; it is only in more advanced age that they become united, either by ramifications from their edges, or by a peculiar membrane. The direction of the fibre, in twisting, is sometimes from right to left, and sometimes the contrary. The size also is very various. In young plants it is very small, so that a millimetre comprises the diameter of 2600 of these fibres; and, in some instances, they have little more than half that size. In older vessels they have a larger size. Between the knots of the trunk, they are simple, and do not ramify, but in the knots they undergo great changes of form, and are variously ramified and combined.

ARTICLE V.

Of the Transformations of the Spiral Vessels.

M. Kieser proceeds next to treat of the transformations or metamorphoses of the simple spiral vessels into several varieties; to which, from their peculiarities of construction, he assigns the names of the annular, the punctuated, the ramified and reticulated spiral vessels, and another variety he calls vessels en chapelet. In essential character and function, however, all these varieties are said to agree; the only difference is, that of external form. Of each of these varieties, we shall subjoin a short description.

The first variety, or rather species of vessel, out of which the others are produced, he calls the simple spiral. It is constructed of one or more fibres, twisted spirally, and placed contiguous to each other, so as to form a round cavity within. In general, the spires of the fibre are in contact, but sometimes there is a space between them. See fig. 51, Plate XV. In the latter case, the side of the vessel is closed by the walls of the adjacent cells, but never by any new production of membrane, either without or within the vessel itself. These simple spiral vessels are found in every young plant, and in the newly formed parts of old ones, and give origin to the other varieties. Their size is smaller than that of others; in some instances they have not more than one-eighth or one-tenth of the diameter of other varieties. They are the only variety found in some of the inferior tribes of vegetables. The number of fibres in each spire varies from one to nine.

Another form of these vessels is that of the Annular annular spiral. In this variety, the component fibre has the form of numerous rings, disposed in a perpendicular line between the ranges of cells; fig. 51, b. These rings are very analogous to the spires of the preceding variety, are of the same size, and are often combined with them in the same vessel. They occur in a great many plants, and, in herbaceous plants, occupy the same position as the simple spiral vessels, that is, next to the pith. The rings of which they are constructed are sometimes separated from each other only by a space equal to their own diameter; but, in other instances, they are separated to eight or ten times that distance, forming then the substratum of the third variety, or punctuated spiral vessel. 42. From the two simple varieties of form just described, other more complicated forms are produced as the plant advances in age. Thus, the third variety, called the punctuated spiral vessel, is constructed by one or more round or flattened spiral fibres; the spires or rings of which, not being connected, leave between them interstices more or less large; which interstices are filled with a membrane more or less thick and transparent, and variously dotted or punctuated, from which circumstance the name is derived.

This structure is imperfectly represented in fig. 51. c, and much more clearly by the letter d of the same figure, in which the white lines indicate the spiral rings, and the intervening dotted substance represents the punctuated membrane; at the top, a portion of the anterior side of the vessel has been removed, so as to display its inner and posterior surface. In this variety, the rings are never contiguous. Such vessels occur only in the more advanced age of herbaceous plants, but seem to be original formations in the albumen of trees. Their size is frequently eight or ten times greater than that of the two former varieties, especially in the stem; but they are much smaller in the root. They always occupy the most exterior part of the vascular fasciculus of herbs, while the two preceding varieties are found next to the pith. In trees, on the contrary, the largest vessels of the annual layers occupy the place nearest to the pith; and all the spiral vessels in these layers belong to this punctuated variety, except those immediately next to the pith. The spiral fibre of these vessels is of very various size. In the largest vessels of this class, its size is greatest; in other instances, it is so small as to be scarcely visible. It is often difficult to determine whether its form is spiral or annular; in herbs, it appears to be spiral; in trees, annular.

43. The membrane which fills the interstices of the spires and rings, and connects them together, is not visible in young vessels; but is produced in more mature age, as is proved by the fact that this membrane is often common to two contiguous vessels, and connects respectively their rings together. Hence it is, that the membrane never surrounds the spires, nor is it surrounded by them, but only occupies the interstices between them; and, from the same cause, the spires themselves are always prominent on the surface of the membrane. In this variety of vessel, the spires cannot be unrolled without tearing their connecting membrane. This membrane, at an early period, is transparent, but becomes opaque from age.

44. As to the points or dots on this membrane, they have by some been taken for pores on the surface; by others for clefts produced by the junction of the spires. M. Kieser confesses that he has not yet been able to satisfy himself on this subject. They are clearly not clefts, and it is against the supposition of their being pores, that their position has always a relation to the spires, and not to the adjacent cells. In the wood of Sassafras, however, these points seemed pierced by a hole exceedingly small; but, in other instances, they appear quite dark, and similar to those which are found on the vesicles that fill the cavity of aged vessels, and where there is not the smallest reason for considering them as pores.

He thinks there is a great analogy between the formation of these vesicular membranes within the vessels, and that membrane by which the spires are connected in this variety of vessel. In some plants, the size of these dots is large, and they appear transparent at the centre; in other instances, they are extremely small. Their form is oblong or elliptical, and they are always ranged in a determined line, parallel, in general, to the direction of the spires.

45. The fourth variety of spiral vessel is said to have the same origin as the last, being formed in part by the spires or rings of the two first varieties; but the interstices between these are filled, not by membrane, but by small ramifications, produced from the rings themselves; and these ramifications are often so implicated as to form a net-work; whence the names of ramified and reticulated spiral vessels. Like the former variety, they do not exist in the young plant, but are the consequence of the gradual changes of advanced age, and produced by a similar series of actions. They are formed of one or more spiral fibres, the spires of which are contiguous in the young plant, but separate at a later period; and the interstices are filled up by new ramifications from the spiral fibre itself. In the first period of their formation, when there are but few ramifications, he names them ramified spirals; and when these become more numerous and implicated, reticulated spirals. They are found but in few plants, and those of the more succulent kind; they do not attain the size of the preceding variety; are associated in the same plant with the simple and annular spirals; and in the fasciculi, occupy the same place as the punctuated spirals, that is, next to the bark. They are more transparent than the punctuated spirals, and occur more frequently in the root than the stem. In the representations given of these vessels by M. Kieser, they appear to differ from the preceding variety, chiefly in the position of the spiral rings, which are more or less obliquely situated, and sometimes send off a sort of branch, as is represented near the bottom of the vessel d in fig. 51.

46. The last variety, or vessels en chapelet, discovered and named by M. Mirbel, are found only in those parts where the perpendicular growth is obstructed, and the vessels, taking a horizontal direction, suffer a complete change of character. It is therefore in the knots of the trunk, in the tubercles of roots, and in similar parts, that such vessels occur. They take their origin occasionally from all the other varieties, and are, in truth, nothing but these varieties changed by the qualities of the knot. They are formed by contractions occurring at short distances, which diminish the diameter of the vessel, and dispose it into the form of irregular oblong cells or utricles threaded on one another, as in fig. 51. e; or as in fig. 11, copied from Mirbel, with which the representations of Kieser nearly coincide; but he makes the figure of the utricles much less regular. The vessel itself also has a tortuous course in the knot, and sometimes many are ramified and combined, so as to form a kind of reticulated appearance. This, however, is effected by vessels leaving one fasci- Elementary culus and passing to another, and does not seem to be a true ramification of one vessel out of another.

The construction of the sides of this variety of vessels is the same as that from which they take their origin. Thus, if they are formed from simple spiral vessels, their sides have the simple spiral form; if from punctuated spirals, then the vessels en chapelet possess the punctuated membrane, and so with respect to the ramified variety of vessels. The contractions in these vessels are not produced by any displacement of the spiral fibres of the other varieties; but their true cause is to be sought in the function of the part, and the action of the knot itself. Every spiral vessel, whether simple, punctuated, or reticulated, may thus be metamorphosed in the knots, into a vessel en chapelet, and again lose this character, and resume its original form in the intermodal spaces.

47. Such is the account given of the construction and metamorphoses of the spiral vessels by M. Kieser. It is, in every part, amply illustrated by figures, made from dissections of various plants. These drawings everywhere support the descriptive detail; and if the microscopical observations from which they are made be correct, no doubt can exist of the truth of the doctrine. That considerable changes do occur in the vessels of plants, after their formation, seems most certain; and the series of appearances exhibited by M. Kieser, presents, as we think, nothing inconsistent with probability, nor beyond the powers of vegetable organization. Neither do they militate against the previous descriptions of Malpighi, Grew, and Hedwig; but, on the contrary, receive, generally, confirmation from them. M. Kieser, however, has pushed his inquiries much farther, and given to the doctrine of transformation a more precise and systematic form. He has not ventured to speculate on the probable causes of these curious changes; but were this the proper place for such discussion, and were the facts, connected with the functions of these vessels, fairly before us, in addition to those which regard their structure, we think that an explanation, tolerably satisfactory, might be obtained. But the prosecution of this subject we must defer to a future occasion.

48. We collect, then, from the whole of the foregoing statements, that all that part of plants, which is commonly stiled the ligneous portion, is composed chiefly of vessels, which, however different in size and external figure, are destined to one and the same office, that of conveying sap; and that these sap-vessels extend from the extremities of the roots to the points of the leaves, and exist in all the organized productions of plants.

This, however, is not the conclusion at which M. Kieser arrived. Though he has demonstrated that the great mass of the ligneous part of plants consists of spiral vessels, and admits that they receive and convey coloured fluids, yet, from the circumstance of their appearing sometimes empty, he regards them, with Malpighi, as tubes destined to convey only air; and supposes the sap of plants to be carried, not by what are called the vessels, but by certain little canals, of doubtful existence, hereafter to be described, and which have been named intercellular canals. (Mém. sur l'Organisation des Plantes, p. 87, 199.) That, however, he should, at the same time, admit the capacity of the spiral vessels to receive coloured fluids, and reject the belief that fluids, destitute of colour, are received by them, is not a little singular; for the colouring particles in the liquor must, and do oppose obstacles to its reception, which fluids of a more simple nature do not experience; and when once such liquors gain admission, they leave behind them traces of their course, which a colourless fluid does not. M. Kieser has altogether overlooked the facts observed by Grew and Du Hamel, of the actual existence of sap in these vessels, both in spring and in autumn; and he seems to be entirely unacquainted with the influence which the development of the leaves, as we shall presently show, exerts on the movements of the vegetable fluids.

49. But it has been the fate of these vessels to experience the utmost licence of opinion in regard both to their structure and functions; nor does it seem probable, that these opinions will soon settle into anything like uniformity. While some have supposed the vegetable to be composed almost entirely of spiral vessels, others limit their presence to a few parts only; and others again altogether deny their existence. Some will have them to be solid fibres; others make them sap-vessels, or nutrient vessels; and others again suppose them to convey only air. Hedwig believed them to convey at the same time both nutrient matter and air; and Bonnet was of opinion that they were entitled to be considered not only as the lungs of the plant, but a sort of muscles also, by which many of its parts executed different movements. (Recherches sur les Feuilles, p. 138.) A late writer, however, and a Professor, it seems, of medicine in the university of Jena, M. Oken, is of opinion, that they ought not to be deemed either simple fibres, or vessels, or lungs, or muscles; but that they execute a function for the plant analogous to that of the nerves of animals; and ought therefore to be named the vegetable nerves. (Kieser's Mém. sur l'Organisation des Plantes, p. 174.) The bare enunciation of such opinions must, we think, be sufficient to ensure their rejection.

50. Rejecting these fanciful and extravagant notions, and adhering to the opinion that the spiral vessels are a variety only of the common sap-vessels of the plant, we shall conclude this branch of the subject with a brief notice of their common modes of termination. If we begin at the root, we may consider these vessels as terminating at that part, by continuation of canal, in the capillary absorbents of the rootlet. As, farther, the vessels of plants, like those of animals, are the only organs which convey the materials out of which, not only the fluid, but the solid parts of the plant are formed; it may, in a general sense, be said, that their modes of termination are as numerous as the kinds of distinct parts or organs which the vegetable system contains. Hence, therefore, as the cellular tissue of plants contains various matters often precisely similar to those which exist in the vessels, it may be inferred, that the vessels have a termination in those organs; and this inference may perhaps carry more weight with many than the attempts before related, of Malpighi and Leuwenhoek, to demonstrate it

VEGETABLE.

Elementary anatomically. Another termination of these vessels must be in certain minute and ill-defined organs called glands, which separate from the mass of fluids peculiar secretions; and a fourth mode may, in the leaves, be in other vessels, which carry back the juices from those organs. The last and fifth mode of termination is into transpiring or exhalent organs, by which a certain portion of the contents of the vessels is discharged: So that in plants, the sap-vessels terminate externally at one extremity in absorbents, by which fluids are received; and at the other in exhaustants, by which these fluids are discharged.

ARTICLE VI.

Of the Proper Vessels.

51. By observation of the natural flow of the sap, combined with the results of experiments made with coloured liquors, we have endeavoured to determine the situation and kinds of vessels by which it is conveyed. The same method will best assist us in ascertaining the nature and place of those which have been called Proper Vessels. Of these also, many species have been described by authors, the existence and characters of which we shall afterwards attempt to ascertain.

52. It was before stated, that, early in spring, the sap of plants rises through the wood alone, and that no fluid whatever is then to be found in the bark. At a later period, however, the case is completely reversed; for the vessels of the wood no longer appear to carry sap, and those of the bark then become abundantly supplied with it. This difference is very clearly and concisely stated by Grew. "The sap," says he, "in many plants, as the Vine, ascends visibly through the wood for a month, in March and April, and rises through every ring of wood to the very centre, yet, at the same time, there arises no sap at all out of the bark, nor between it and the wood." "But late in spring," he continues, "and in summer, the sap is no longer visible in the wood, but is abundant in the bark, in the inner margin adjacent to the wood." Du Hamel too remarks, that when the lymph rises abundantly through the wood in spring, the bark is dry, and adheres to the wood, and no sap then issues from it, nor from between it and the wood; but, later in the season, he adds, the bark yields abundance of sap. These statements have been verified by the multiplied observations of various subsequent authors.

53. But why is the sap thus present only in the wood at its first rising in spring? Why at a later period does it cease to be visible in that part? And how and why does it afterwards find a passage into the bark? Some observations of Du Hamel, Hales, and Walker, point, we think, to the true cause. In spring, says Du Hamel, when the sap rises vigorously, the buds have not appeared; when they begin to open, the sap then flows less freely; and when the leaves are fully developed, then the flow of sap entirely ceases. Dr Hales also remarks, that, towards the end of April, when the young shoots come forth, and the surface of the Vine is greatly increased by the expansion of the leaves, the sap then ceases to flow in a visible manner till the return of the next spring. All bleeding trees, he adds, cease to bleed, as soon as the young leaves begin to expand enough to perspire plentifully, and draw off the redundant sap. The bark of Oak, too, separates easily when lubricated with sap; but before the leaves appear and perspire, the bark will no longer run (as they term it), but adheres most firmly to the wood. (Vegetable Statics, 3d edit., p. 126.) In like manner, in an experiment of Dr Walker, a Birch-tree bled from every perforation in its trunk, and from every cut extremity of its branches, until vernation or budding began; then the bleeding was almost immediately checked, and when the young leaves had pushed beyond the hybernaculum, the bleeding entirely ceased. (Edin. Phil. Trans. Vol. I. p. 31.)

It is however certain, that though the sap was no longer visible in the wood after the leaves were developed, it continued nevertheless to rise through it; for in no other way could the leaves obtain the large portion of fluid which it is known that they constantly discharge by transpiration; and coloured fluids manifest their presence in the vessels of the wood, as well after as before the development of those organs. The leaves, therefore, must be regarded as the organs which, by their perspiration, draw off, as Dr Hales observes, the redundant sap; and hence in an experiment, where a notch was cut two or three feet above the lower end of a stem, though a great quantity of sap passed by the notch, yet was it perfectly dry; because, says he, "the attraction of the perspiring leaves was greater than the force of suction from the column of water." (Veg. Statics, p. 111.)

54. Not only, however, does the development of the leaves render the sap no longer visible in the wood; but they also appear to be the organs by or through the bark which it finds its way to the bark. In all the experiments just recited, the bark continued dry until the sap disappeared from the wood; in other words, until it was drawn off by the leaves; and then, and not till then, the bark became moist, and continued laden with sap through the rest of the summer. Now, as it has been before shewn that no sap enters the bark by the roots, nor gets into it directly from the wood, there is no other known channel by which it can be conveyed, except through the leaves; and these, therefore, necessarily appear to be the organs by which it is apparently carried off from the wood, and by or through which it, at the same time, finds its way to the bark.

This inference appears to follow, not only from the fact of the bark continuing dry until the leaves are developed, but from the circumstance that it is again rendered dry, after having become moist, if these same leaves be removed. If, says Du Hamel, we remove the leaves of a young tree, when in full sap, and whose bark is easily detached, in a few days after the same bark will adhere as closely to the wood as it commonly does during winter. This direct connection between the leaves and bark, is also well illustrated in an experiment of Hales, employed by him for a very different purpose. From two thriving shoots of a Pear-tree, he cut, in several places, half an inch of the bark off all round. All the ringlets of bark between these incisions had a leaf-bud upon them except one, and all but this Elementary one ringlet grew and swelled at their bottoms till August; and the larger and more thriving the leaf-bud was, so much the more did the adjoining bark swell. (Veg. Statics, p. 149.) Mr Knight also found the bark of the Vine to become shrivelled and dry when the leaves were stripped off; but in those parts in which it communicated directly with the leaves, it continued moist and flourishing. (Phil. Trans., 1801, p. 335.)

55. By connecting, therefore, the circumstances attending the flow of sap with the development of the leaves, we gain satisfactory reasons for all the apparent anomalies observed to attend its course. In spring, before the appearance of the leaves, no natural outlet for the escape of the rising sap exists, and therefore, when the vessels are cut or perforated, they readily pour out their sap, or bleed; but late in spring, and in summer, when the leaves are developed, the more watery parts of the sap are thrown off by transpiration; and, while this process proceeds, the fluids do not then accumulate in such quantity in the minute vessels of the trunk, as to be effused, or bleed through their cut or perforated sides. A cold day, however, or a moist and still atmosphere, by checking transpiration from the leaves, restores more or less the propensity to bleeding from the trunk; and in autumn, when fructification begins, and vegetation makes a pause, the same disposition to bleeding recurs in the trunk, from the check imposed on the more active powers of growth.

56. It is farther evident, that, when the vessels of the bark become supplied with fluid, they could not have derived it immediately from those of the wood, since, in these different parts, the fluids have frequently no sort of agreement in properties. Thus, Grew remarks, that almost all plants, late in spring and in summer, bleed from their bark; and the sap has either a sour, sweet, hot, bitter, or other taste. At this period, the bark of the Vine yields a sour sap; but, "what is vulgarly called bleeding in the Vine, is," he adds, "quite another thing, both as to the liquor which issueth, and the place whence it issues—that is—it is neither a sweet nor a sour, but a tasteless sap, issuing, not from any vessels in the bark, but from the air-vessels of the wood." (Anatomy of Plants, p. 125.) Malpighi also was well aware of the difference in the qualities of the sap, and thought every plant possessed its peculiar sap; but he has not so accurately defined the situation of the vessels that contain it. Du Hamel, however, points out distinctly the difference of quality in the sap of the bark and wood. In the bark of some plants it is white; in others red; and in others yellow: It is in some instances milky; in others resinous; and in others gummy. In many plants it has a sweet taste; in some it is caustic; and in others insipid. It has sometimes much odour as well as flavour, and frequently it is destitute of both. (Phys. des Arbres, Tom. I. p. 68.)

57. But, if the qualities of the sap in the bark be acquired in thus different from those of the sap in the wood; if the leaves, these peculiar qualities are detected in it, only after the development of the leaves, and the leaves be the organs by which alone the sap can be conveyed from the one part to the other—then it seems to follow, that the sap must acquire these new properties in the leaves, during its transmission through them. Malpighi remarked the existence of this altered sap in the leaves, and held them to be the organs which prepared nutrient matter for the plant; and Dr Darwin, by immersing plants of Spurge in coloured liquors, not only saw, as others had previously done, the red fluid ascend through the leaf; but another fluid, of a white colour, returning, at the same time, from the extremities of the leaf, and descending into the petiole. (Botanic Garden, Vol. I. Notes, p. 450—453.) This same returning fluid, Mr Knight observed, in similar experiments, on branches of the Apple and Horse-Chesnut trees, and even traced it through the petiole into the inner bark, by the vessels of which, it seemed to be conveyed to the extremities of the roots. (Phil. Trans., 1801.) The motion, therefore, of the sap in the bark, is not that of ascent, as Grew and Malpighi and many others have believed; but of descent, as the observations and experiments of De la Baisse, Du Hamel, Knight, and others, abundantly prove. To these vessels of the bark, Grew assigned particular names, according to the apparent quality of the fluid they conveyed. Malpighi gave them the general appellation of vasa peculiaria, from their containing a fluid different from the common sap. By others they have been called cortical vessels, a term, however, not applicable to many tribes of vegetables which are entirely destitute of bark. Lastly, Du Hamel and others denominated them proper vessels, which term differs but slightly from the appellation of Malpighi, and, though not very precise, is that we shall continue to employ.

58. From regarding the newly formed vessels of

The view thus presented of the course of the sap, and the modifications which its movements and qualities experience from the development of the leaves, may assist in the determination of the important and long-agitated question regarding the proper period of felling timber, as it relates both to the bark and wood. The most proper period for the timber, is doubtless that in which it is most dry or destitute of sap; and the properest period for the bark, both as regards its chemical condition, and the facility of stripping it, is, when it is most succulent, and filled with its "proper juices." But these respective periods and conditions do not happen to coincide, and therefore, the time at which the wood is in best condition, is that in which the bark is in its worst; and vice versa. If, therefore, the qualities of the bark dictate the period of felling, it will be late in spring or in autumn, when it is most abundantly filled with its proper juices, and of course, when the wood also is necessarily filled with fluid, and in an active state of vegetation; if, on the other hand, the condition of the wood regulate the period, then it will be late in winter, or before the sap rises in spring, when the wood is destitute of sap, and the bark, of course, is necessarily dry and adherent. To reconcile these opposing conditions, it seems desirable, as far as it may be practicable, to strip the Elementary the wood as part of the bark, Grew uniformly represents the bark as possessing two distinct species of vessels, in which he has been since followed by several other writers; but the vessels which he calls lympheducts belong rather to the wood, so that we may regard him as describing only one species of proper vessels. In herbs, these vessels stand sometimes in distinct parcels or columns; sometimes they are disposed in a ring; sometimes they have a radiated position; and sometimes they are more intermixed with the sap-vessels, and seem to alternate with them. In trees, the vessels of the bark are more distinct, and have a much more regular appearance. They are commonly postured near the inner margin of the bark, and, when viewed in a longitudinal direction, seem collected into fasciculi which are more or less numerous, and the component vessels of which continually diverge and join with others, so as to form a reticulated appearance; as in fig. 18. Plate XV. Of these reticulated fasciculi, many layers exist in an old tree; and to these layers the thickness of the bark is chiefly owing. As they proceed inward, the direction of the fasciculi is less oblique, so that near to the wood they are almost straight: Hence, the spaces formed by the reticulations are very unequal, often large in the exterior part of the bark, and diminishing in size towards the wood; they are everywhere filled with cellular tissue. Such is a general description of the proper vessels of the bark as given by Grew, Malpighi, and Du Hamel. The organs here described, we regard as truly vessels; but some writers have also described, as vessels, various collections of the proper juices which occur in different parts of the cellular tissue of the bark, and have thus lost sight altogether of the anatomical characters which distinguish vessels from cells.

59. The vessels which thus form the vascular portion of the bark appear to differ but little in structure from the more simple vessels of the wood. Grew considered them to possess a similar structure, from believing them to be formed by the inner bark, at the same time with the vessels of the wood; and, therefore, he adds, "they may be reasonably thought similar in the bark and wood." (Anat. of Plants, p. 112.) Malpighi regarded them as simple tubes, containing sometimes peculiar juices, but advances nothing particular respecting their structure. (Anat. Plantarum, p. 3.) M. Mirbel's opinion deserves some notice, insomuch as he declares the structure of these vessels to differ entirely from all those of the wood. Their sides, says he, are perfectly entire; they have neither pores nor clefts, and may therefore be deemed simple tubes. (Exposit. de la Théorie de l'Organisation Végétal, p. 109). A single vessel of this kind is represented in Plate XV. fig. 16; and in fig. 17, a fasciculus of the same vessels magnified, is given, as delineated by M. Mirbel. A remark also of Hill, if it be deemed to rest on correct observation, is entitled to great attention. "The vessels of the bark that form the fasciculi are not," says he, united to each other, but are connected with the cellular tissue at numerous places, and, when separated from it, there appear on the sides of the vessels small oval depressions, dotted as it were with pin-holes." (On the Construction of Timber, p. 28.) These appearances he regards as of a glandular nature, but their description corresponds better with that of Leuwenboeck respecting the lateral ramifications from the vessels of the wood; and they may probably be the points at which communication is effected betwixt the vessels and cells.

60. The cause of the reticulated appearance which the vessels of the bark exhibit in trees, is doubtless to be attributed, as we think Du Hamel somewhere remarks, to their peculiar mode of growth. A new layer of cortical vessels is every year added to the inner surface of the bark, as well as a new layer of ligneous vessels to the outer surface of the wood; so that, as Grew observes, the new matter of the tree is every year distributed two contrary ways; one part falling outward towards the bark, and the other part retaining its situation inward to constitute the wood. At first, the newly formed cortical vessels are straight, and stand parallel, like those of the wood; but, by the continual growth of the new parts, formed between the bark and the wood, the older vessels of the bark are gradually forced outward, and being thus every year disposed around a larger cylinder, are necessarily more and more separated from each other, and produce at length that net-like form which we observe them to possess. The newly formed vessels of the wood, on the other hand, retain their original position, and, therefore, preserve their parallelism, seldom or never exhibiting those flexures and reticulations so common to the vessels of the bark.

61. In the bark, as well as in the wood, the vessels are found to possess different sizes. In the Pine, vessels containing turpentine are represented by Grew, which are very much larger than the common sap-vessels, and are surrounded by smaller ones, exactly as the large spiral tubes of the wood are said to be ensheathed by the common sap-vessels. The milky juice of a species of Sumach is contained in very large vessels, disposed so as to form a ring, and each large vessel is surrounded by many smaller ones. (Anat. of Plants, Tab. 20.) The appearance of these large vessels in one species of Pine, is well represented by Hill, and the account he gives of their formation is probably correct. In this tree (Pinus orientalis), some of these vessels form oval openings, large enough to admit a straw; these openings occupy the centre of the bark, and are surrounded by a ring of smaller vessels; as their contents are soluble in alcohol, it is easy to obtain them empty. In fig. 19. Plate XV. the vessels of this tree, as they appear in the bark, are displayed; the woody portion of the tree has been scooped away, so that the longitudinal aspect, as well as the transverse sections of them, is exhibited. From a strict inquiry into

tree of its bark while standing, in autumn, at or a little before the period of fructification, when the bark must possess its richest qualities, and be in the best condition to separate; and to fell the tree late in winter, when the wood is destitute of sap, and its vegetative powers are most completely suspended. their nature, Dr Hill concluded that these larger vessels were originally the same as those of the smaller fasciculi in the bark of the same tree; "so that, if we conceive one of these smaller fasciculi opened in its centre, and the vessels driven every way outward, till they are stopped by the substance of the bark, we shall have an idea of the structure of this large vessel, which is nothing more than a great cylindrical hollow formed in the centre of such a fasciculus." (Hill on the Construction of Timber, p. 29.) It is in trees that have copious and viscid juices, that these enlarged vessels are formed; and where the juices do not concrete, it is probable, that, as the vessels annually recede from the centre, they suffer a reduction in size, from the continued effects of desiccation and compression to which they are exposed.

62. The foregoing varieties appear alone entitled to the appellation of the proper vessels of the bark. In many tribes of vegetables, however, as will afterwards be shown, no distinction of bark and wood exists; but one uniform distribution of vessels extends from the centre to the circumference of the plant. Such plants have also their proper vessels, but the place and disposition of these vessels are not so precisely ascertained. From the mode in which their growth is accomplished, as well as from observation of their structure, it may be inferred, that their proper vessels are distributed through the whole substance of the plant, accompanying, in every part, the sap-vessels. In some plants, possessing this arrangement of parts, such as different species of wheat, Malpighi describes and delineates a vas proprium as forming a part of each fasciculus of vessels; and a similar intermixture of the two kinds must, we conceive, exist in all similar structures.

63. Even in many plants, possessing a distinct bark, vessels containing proper juices are found in the wood. In every circle of wood, from the inmost that surrounds the pith, to the outmost in contact with the bark, vessels containing a gum, turpentine, or some other concrete or coloured juice, may frequently be found. Malpighi conceived them to exist in all plants, though, from the nature of their fluids, they could not always be distinguished; and he believed them to afford a highly perfect juice for the nutrition of the plant. According to Grew, "the turpentine vessels that are scattered up and down the wood of the Pine and Fir are the self same which did once appertain to the bark; but being pinched up by the wood, they are become much smaller pipes." (Anat. of Plants, p. 115.) Du Hamel also regarded them as similar to those of the bark, but rendered much smaller by compression. In the Pine and Fir, they are disposed circularly around the axis, much like the sap-vessels, and alternate with them. (Phys. des Arbres, Tom. I. p. 41.)

In Piscidia erythrina, the proper juices are of a scarlet colour, and the vessels that contain them are therefore readily discerned wherever they exist. This plant has been selected by Hill to demonstrate the position of these vessels. In the bark, they are collected into fasciculi, all the vessels of which contain coloured juices, and are disposed in a ring on the inner margin of the bark. Within this ring stands the albumen, through the substance of which many smaller red vessels are distributed, and similar red vessels are more sparingly seen in every layer of wood, particularly in that which envelopes the pith. (Constr. of Timber.)

64. Now, the red vessels thus observed in the wood of the above mentioned plant, must either have been formed in the situations they occupy, or transported from some other place. The latter supposition is inadmissible, insomuch as the wood of trees is formed by layers of new vessels superimposed on one another; and no removal of the old vessels, nor reproduction of new vessels within the old layers, ever takes place; consequently, no actual transposition of vessels could occur; nor could new vessels be developed in the wood after it had been completely formed. If, however, an alternate deposition and absorption of matter go on into, and from the cells, it is possible that the vessels might, in this way, become filled with a matter different from that which they originally possessed; but in the case before us, a readier explanation presents itself. The new matter of the wood is formed at the same time, and in the same place, as that of the bark; and through this new woody matter the red vessels were dispersed as well as in the bark. Consequently, every addition made to the ligneous layers would furnish some vessels that contained these proper juices; and this being annually repeated, would exhibit that intermixture of proper vessels with sap-vessels, which is observed in all the ligneous layers of this and many other trees. Hence these proper vessels of the wood must be held to retain the position in which they were originally produced; and cannot be said to have approached nearer to the centre, but only, by the addition of new layers exterior to them, to be placed farther from the circumference of the tree. As Grew, therefore, held the albumen to be a part of the bark, he might correctly say that these vessels "did once appertain to it."

Article VII.

Of Collections of the Proper Juices in the Cellular Tissue.

65. Beside this accumulation of the proper juices in certain vessels of the wood, it frequently happens that depositions of similar matter occur in all parts of the cellular tissue of plants. In the bark of the single Oak and Poplar, and of other trees, resinous concretions are often found in the cells; they are situated irregularly, and, according to Malpighi, are observed even in very young bark. Sometimes the cells containing milky and resinous juices are so postured in the bark, says Grew, as to form cylindrical channels, which are neither parallel nor anywhere inclosed, but run, with some little obliquities, distinct from one another. They appear to be formed out of the cells, and are not bounded by any walls or sides proper to themselves, but only by those of the cells. (Anat. of Plants, p. 112.) They are often short and tortuous, always isolated, and are sometimes placed irregularly; at others, disposed in a circular form. They occur sometimes in the pith, and possess very different sizes and figures. They have fre- Elementary quently been deemed a species of proper vessels, from the mere circumstance of their containing similar juices, and from possessing sometimes an elongated form; but they are organs which, neither in form nor in function, bear any resemblance to vessels. Mirbel proposes to name them secretory canals, and M. Link cellular reservoirs; the term certainly most generally applicable, and involving no hypothesis respecting either their formation or functions.

66. The manner in which these cellular reservoirs may be produced in the bark or pith, is readily explained, on the supposition that a communication everywhere subsists between vessels and the cells. One set of vessels has been shown to receive and carry out sap to the leaves, and another to bring it back from them to the bark; and these latter vessels are everywhere, in their course, surrounded by cellular tissue. Hence the cells, in every part, may receive a portion of the fluid which the vessels are employed to convey. Thus in herbs, the cells both of the bark and pith are filled with fluid, which led Grew to believe that the sap was actually transmitted through those organs; but at the same time he delivers facts which, even in his own opinion, prove that it is derived directly from the vessels. Not only in herbs, but "in every annual growth, whether of a sprout from a seed, of a sucker from a root, or of a seyon from a branch, the pith is always found the first year full of sap; but in the second year, the same individual pith always becomes dry, and so it continues ever after. One cause whereof is, that the lympheducts of the bark being, the first year, adjacent to the pith, they do all that time transtuse part of their sap into it, and so keep it always succulent. But the same lympheducts, the following year, are turned into wood, and the vessels which are then generated and carry the sap, stand beyond them in the bark; so that the sap, being now more remote from the pith, and intercepted by the new wood, cannot be transmuted with that sufficient force and plenty as before, into the pith; which, therefore, from the first year, always continues dry." (Anat. of Plants, p. 124.)

All that is here said respecting the transusion of the common sap from the vessels to the cells, as it ascends through the wood, is equally applicable to the proper juices as they descend through the bark. During the first year of growth, both the sap and proper vessels are adjacent to the pith, as well as to the bark, and each order may therefore transtuse its fluids into the cells of either. The common sap, from retaining its fluidity, is frequently removed by absorption, and the cells that contained it appear empty and dry; but where the proper juices are transtused, and become viscid or concrete, they are retained, and appear in different quantities and forms both in the bark and pith, according to the nature and properties of the juices from which they are derived, and the texture and situation of the tissue into which they are poured.

67. To these collections of the proper juices in cellular Canals the cells of the cellular tissue may be referred the opinions of those who describe them as existing sometimes in vacuities betwixt the cells. M. Treviranus professes to have discovered certain interstices between the cells, formed in a mode hereafter to be explained, to which he has given the name of intercellular canals. According to him, these canals contain the proper juices, and convey them to all the cellular parts of plants; and are the true proper vessels of the bark. We before saw that M. Kieser, after making the wood to consist almost entirely of spiral vessels, and then converting these vessels into tubes destined only to convey air, supposed the sap to be carried by these same intercellular canals. (Kieser's Mém. sur l'Organisation des Plantes, p. 36.) With M. Treviranus he also considers them as the real proper vessels of the bark, by which alone the juices are conveyed to all parts of the cellular tissue. (Ibid. p. 216.) If such canals really exist betwixt the cells, it is probable, that, like the cells themselves, they may sometimes become reservoirs of the proper juices; but simply on that account, to pronounce them vessels, is, in an anatomical sense, exceedingly incorrect; and to make them afterwards supersede the existence of the real vessels themselves, seems nothing less than downright extravagance and absurdity. Were there any truth in such statements, we might at once banish from the organization of plants all the varieties of vessels, whose situation, structure, and characters we have been labouring to describe and define. But the opinions of these writers have not at all shaken our faith in the facts observed by their predecessors; and as long as the vegetable functions shall continue to be exercised as they have hitherto been, so long, we believe, will a vascular system, such nearly as we have attempted to demonstrate, be employed as the chief instrument in their execution.

Section II.

Of the Absorbent and Exhalent Systems.

Article I.

Of the Absorbent System.

68. Connected with the vessels that distribute the fluids through organized bodies, is another system of vessels by which extraneous matter is taken up to support the growth of parts, and supply the waste occasioned by the exercise of the various functions. To these vessels Anatomists have given the name of Absorbents. The function which they perform is carried on either from the external surface, or from some internal part of the body; and its exercise, in animal bodies, may be distinguished into three kinds or stages. The first is that in which new or extraneous matter is taken up and added to the system, as in the absorption of substances from the skin, or of chyle from the intestines; the second is that in which substances previously separated from the fluids by secretion, but without becoming organized, are again taken up by the absorbents, and reconveyed into the blood-vessels, as in the absorption of milk, bile, and fat; the third kind is that in which the secreting organs themselves, and successively all the solid parts of the body, are removed by the action of the absorbent vessels. By plants, this function is exercised to less extent, and seems to comprise only the two first kinds or degrees of it, viz. the primary absorption of extraneous matter, and the reabsorption of certain any power of reabsorbing what has once formed an organized part of the system. Hence the formation of organized parts in plants is not accompanied, as in animals, by the unceasing removal of old particles; but the particles, which have once become organized, continue permanent, until removed by some cause or process foreign to the living powers of the plant. When once, therefore, the organs of plants have become mature, they are exposed to decay only from the operation of foreign causes, and cannot be mined from within by that gradual loss of balance between the secreting and absorbing functions, which the advances of age bring on the animal system. Neither in the vegetable system can the removal of organized parts under disease, any more than in health, have place; and consequently, the several modes or stages of ulcerative absorption, so finely illustrated by the researches of Mr Hunter, belong not to the economy of plants.

69. As the function of absorption is thus of more limited extent in plants than in animals, so may we expect to find the arrangement of organs destined to its exercise. In animals, the absorbent vessels are quite distinct from those which carry blood, are provided everywhere with glands, and, like the veins, are furnished with valves. From their beginnings, in all parts of the body, to their termination, they continually unite with one another into vessels successively increasing in size, until, after a long course, they form at length two trunks, which deliver their contents into the large veins near the heart. As no common reservoir exists in plants, there is no such single point to which their absorbed fluids require to be carried. Hence their absorbents seem everywhere to have a very short course, to form no union with one another, but to deliver their contents at once into the sap-vessels adjacent to them. They appear to be destitute alike of glands and valves, and indeed, in an anatomical view, they can scarcely be considered distinct from the sap-vessels, but may rather be deemed ramifications from them; so that although we grant, with Grew, that the ordinary sap-vessels do not ramify one out of another, yet they certainly send off those fine ramifications which, from their office, we denominate the absorbents of plants.

70. In the root, the absorbents are capable of being demonstrated: when a plant is immersed in coloured fluids, many of its capillary absorbents become tinged through their whole course to their termination in the sap-vessels, proving them to be simple ramifications from these vessels themselves. A farther proof of the identity of these two systems is derived from the fact, that any part of a sap-vessel is not only capable of emitting capillary absorbents from its sides, but of exercising itself an absorbent function, whenever its cut extremity is brought into contact with a fluid. These absorbents are formed very speedily, and in great multitudes on the roots of annual plants; and even in perennial plants, they appear, like the leaves, to suffer an annual decay, and be reproduced with the return of vegetation.

71. But plants absorb fluids by other parts of their surface as well as by the roots. This absorbing power extends, in some of the lower tribes, over the entire surface of the vegetable, which is destitute of any organ analogous to a root; in other instances, where the roots are small and the soil arid, the plant derives almost all its moisture by the absorption of dews through the leaves. The experiments of Bonnet show that all leaves, both those of herbs and of trees, when brought into contact with water, are capable of absorbing it, and that the moisture thus absorbed is communicated through the vascular system of the leaf. The leaves of herbs he found to absorb nearly alike from either surface; but those of trees absorbed best by the lower surface. The petiole and larger rilets appeared to absorb much less than the other parts of the leaf. So great and general is this absorbing power, that vegetables, says he, may be said to be planted in the air, nearly as they are in the earth, the leaves being to the branches what the capillary rootlets are to the roots. (Recherches sur l'Usage des Feuilles, p. 22, 47.)

72. What then are the organs by which this function is carried on in the leaf? M. Bonnet imagined the vessels of the leaves to receive their fluids by Pores, through the pores adjacent to them; and that the leaves, which had only few pores, possessed but little absorbent power. (Ibid. p. 20, 22.) He thought, also, that the hairs frequently distributed over the leaf, attracted moisture, and might even act as absorbents; though he admits that many leaves which have only slight inequalities on their surface, without hairs, exercise an absorbent function. (Ibid. p. 47.)

This subject has been since investigated by M. Decandolle, whose researches appear to confirm the account of Bonnet, as to the absorbing power of the pores. According to him, these pores are found on all parts of the leaf except the rilets, which have none, but are covered with hairs. At the mouth of the pore, a vascular net-work is always to be found, which he regards as a production from the larger vessels of the leaf. He asserts that pores are found only in those parts where vessels go to terminate, and not in others; and that in trees, this structure occurs chiefly on the lower surface of the leaf, while in herbs it is equally seen on both surfaces. The stem, in general, has few or no pores, except where it is soft and herbaceous; and even then, the pores occur only in the deeper green furrows, not on the prominent lines which bound them, and are usually covered with hairs. No pores are to be found on roots or bulbs or fleshy fruits, but most of the organs above ground are more or less furnished with them. Exposure to the air seems necessary to their formation; for plants, or parts of plants, that live beneath water or earth, are destitute of pores, but acquire them if brought into the free air. Exclusion of light prevents also the formation of pores; and hence etiolated plants are not furnished with them. (Mém. de l'Inst. Nat. Tom. I. p. 351.) In general, his anatomical researches, respecting the existence of pores in leaves, agreed with the results of Bonnet's experiments on the absorbing power of their surfaces; and when we consider that all plants, and parts of plants, secluded from the air, are at the same time destitute of pores, and of the power of absorbing by their surfaces, it may be inferred that the organs of absorption, on the external surfaces of Elementary plants, are the minute vascular productions, which in tender and succulent parts exposed to the air and light, everywhere perforate the cuticle, and form in it those innumerable orifices which we denominate pores.

73. But the function of absorption in plants, is not confined to the taking up of extraneous matters. Many facts prove that, in every part where active vegetation exists, internal absorption is continually going on. The organs by which it is immediately performed cannot, perhaps, from their extreme delicacy and minuteness, be rendered capable of anatomical demonstration; but certain facts which occur in plants, coupled with certain analogies derived from other organized textures, must, we think, carry complete conviction of their existence. In almost every part, and on every surface of animal bodies, the vessels which exercise absorption may be traced; but the mouths or orifices by which they actually absorb, are scarcely ever to be seen. In one instance only, viz. in the intestines, have they been followed to their beginnings, and discovered in the act of exercising their appropriate function. (Gordon's System of Human Anat. Vol. I. p. 70.) But though their orifices remain, in other parts, undiscovered, no anatomist hesitates to admit their existence when he sees the canals of the vessels themselves laden with blood, or milk, or bile; and seeing them thus to convey fluids, whose colour manifests their presence, he equally believes them capable of absorbing and conveying other substances, though they may not be visible to the eye. Believing farther, that no solid part of the body, nor even fluid part that has been deposited in closed cavities, can be removed in a natural manner from its place, but by the agency of these vessels, he comes to regard the simple fact of the disappearance of such part, as sufficient evidence of its absorption.

74. Now the facts and analogies on which internal absorption rests in the vegetable system, are precisely of the same nature, and the evidence of its existence is scarcely less complete. In every part of the cellular tissue of plants, various substances have been found, which must have been primarily derived from the vessels, the only organs which furnish new materials to the plant. These substances, however, often disappear from the cells, and are again to be detected in the vascular system. Thus, in the seed, as will afterwards be shown, the cells of the cotyledon contain a solid unorganized matter, which could have been originally deposited in them only by means of the vessels. During germination, this solid matter is rendered fluid, disappears from the cells, and is again to be traced in the vessels on its way to afford nutriment to the radicle and plumule. We say then that this unorganized matter must have been taken up from the cells of the cotyledon, and conveyed into the vascular system, by the agency of absorbent vessels, which, it is probable, are distributed everywhere on the inner surface of these cells; just as, in the animal system, absorbent vessels are considered to take up the fat from the surface of the cells in which it is deposited, and convey it into the vessels of the animal.

75. This alternate absorption and deposition of the nutrient matter of seeds, is sometimes strikingly displayed in the growth of potatoes. It frequently happens that potatoes, lying in a damp cellar, put forth shoots which grow to a considerable size without the access of any foreign agents, except heat, water, and air. On these shoots, young potatoes, as large as the eggs of pigeons, are sometimes to be found, and the substance of the old potatoe has in great part disappeared. In such cases, the matter from the cells of the old potatoe, must be considered as removed by absorption, and conveyed into the vessels of the shoot, where it was in part employed in forming the new organs of the young potatoe, and in part deposited, to experience, perhaps, in some future growth, similar successions of removal and deposition. In the living parts of perennial plants also, nutrient matter appears to be alternately deposited and absorbed from the cells during the active periods of vegetation; and in the cellular tissue of herbaceous plants, a similar deposition and absorption of fluids seems to be frequently taking place; so that in all the vegetating parts of plants, these alternate functions of secretion and absorption are more or less constantly exercised.

76. A good illustration of the manner in which these functions are alternately exercised, is afforded by an experiment of M. Decandolle. The parasitic plant called Mistletoe draws its nourishment, as is well known, from the tree on which it grows. M. Decandolle placed a branch of an Apple-tree, bearing a stalk of mistletoe, in an infusion of cochineal for five days. He then dissected it, and observed the coloured liquor to have risen through the wood and albumen of the apple-branch, and reached the place of junction between it and the mistletoe, which it strongly reddened; and from thence it penetrated into the woody part of the mistletoe. There did not, however, appear to be a true anastomosis between the vessels of these different plants; but, at the base of the mistletoe, where the parts were so deeply reddened, a minute cellular structure was observed. Into these cells the vascular system of the apple appeared to deposit its sap, and from them the capillary absorbents of the mistletoe, distributed upon the cells, seemed, like the ordinary absorbents of roots, to take it up. (Mém. de l'Instit. Nat. Tom. I. p. 370.) From these and many similar facts it may be inferred, that absorbents, communicating with the vessels of the plant, exist in every part, and that the removal of all secreted matters from the cells and other closed cavities of the vegetable, when effected by the living powers of the plant, is accomplished, as in animal bodies, by the exercise of an absorbent function.

ARTICLE II.

Of the Exhalent System.

77. But from their external surface, and from the organs of the same parts as we have seen to exercise an absorbent function, plants, in certain circumstances, give off a large quantity of fluid by transpiration; and the organs by which this function is performed, seem, from many considerations, to be the same as those by which, under other circumstances, absorption is accomplish- This function of transpiration is common to all terrestrial plants, and all are more or less furnished with pores; but it does not occur in aquatic plants, according to Decandolle, which are destitute of pores. Fleshy plants and the petals of flowers, which have but few pores, transpire little, and etiolated plants, which are destitute of pores, do not transpire at all. On the contrary, herbaceous stems and plants, which have numerous pores, throw off most fluid by transpiration. This general agreement between the existence of pores, and the exercise of the transpiratory function, leads to the presumption that they are the orifices through which the fluids are discharged; and if it be admitted that these pores are situated at the extremity of the fine ramifications that come off from the vessels, their fitness for such an office cannot be denied. Comparing these facts, regarding transpiration, with those previously stated concerning absorption, M. Decandolle is led to conclude that the pores on the surfaces of plants are the organs by which these functions are alternately carried on, according to the existing condition of dryness or humidity in the surrounding atmosphere.

78. Repulsive as this conclusion may at first seem to our ordinary conceptions of organized bodies, yet there are many circumstances in the structure and habits of plants that give it great probability; so much so, that we ourselves had long since reached the same point by a route different from that pursued by M. Decandolle. It is highly probable, that the exhalents of the leaves are simple ramifications from the larger vessels, like the capillary rootlets; and as they have no valves in their canal, there is no mechanical impediment to their exercising an inverted action. The sap-vessels themselves readily absorb, even coloured fluids, when inverted; and though their exhalent terminations are too fine to receive such fluids, yet why may they not, like the trunks from which they spring, be capable of taking up ordinary fluids in that manner? The fluids absorbed through the leaves must at once enter the sap-vessels, for there is no common reservoir to which they can first be carried; and it is extremely improbable, that, from the same parts of the same vessels, exhalants and absorbents, capable of exercising only opposite functions, should at the same time arise. In the animal system, the exhalants spring from arteries, and the absorbents terminate in veins; but in the less complex structure of plants, it seems demonstrable, that both orders of vessels must at once communicate with the same sap-vessels. It is, therefore, more probable to suppose, that, instead of two distinct orders of vessels, as in animals, one only should be provided, capable, under different circumstances, of exercising different functions. This vicarious office of the organs, under consideration, leads to no confusion in its exercise; for the condition of the atmosphere, which favours transpiration, is that which removes from the leaves the power of absorption; and, on the contrary, absorption occurs only in a humid atmosphere, when, as Hales has shown, little or no transpiration takes place.

79. The view thus presented of the external absorbent and exhalant vessels, may probably be extended to the minute vascular productions which seem everywhere to spring from the vessels internally. If secreting and absorbing vessels be held to exist in every part of the plant, they must every-sorbing where communicate with the vascular system; for it is from the vessels of this system that the matter of their secretions is primarily derived, and it is into the same vessels, that, in many cases, these secretions are subsequently returned. Nor does the exercise of the two functions of secretion and absorption in plants present any apparent obstacle to the supposition of their being performed, at different times, by the same organs. Thus, when nutrient matter is deposited in the cellular tissue of the seed, it is destined only for a future use, and the purpose of nature would be defeated, were an absorptive function to be, at the same time, employed for its removal. On the other hand, when this matter is again taken up, during the germination of the seed, no secreting function seems then to be exercised in that part; for the organ itself, in many seeds, gradually wastes, and no fresh matter is deposited in it. Even when the cotyledon, to a certain extent, augments in size, its nutrient matter is continually drawn off for the support of the radicle and plume, and no fresh matter of the same kind seems to be then deposited; so that the same vessels, which formerly exercised the function of secretion, may, without disturbing the economy of the plant, be now employed in the exercise of absorption. As thus the two functions do not require to be performed, in the same part, at the same time, they may, if nothing else forbid, be exercised at different times by the same organs. In the animal system, where the organs themselves are removed, secreting and absorbing vessels must necessarily co-exist; and to maintain the integrity of parts, their functions must proceed at the same time, and, to a certain extent, balance each other; but, as no similar operations appear to be carried on in the vegetable system, no such complex organization is required to sustain them.

Section III.

Of the Cellular Tissue.

Article I.

General Description and Character of the Cells.

80. The elementary organ, denominated cellular tissue, may be said to consist of a membranous substance, disposed into a great number of small circumscribed cavities, connected with each other, and arranged in rows or suites, generally in a direction that cuts at right angles, the perpendicular tubes which represent the vascular system. From Grew, it received the appellation of parenchyme, a term still often used in describing different parts of this tissue; by Malpighi, it was called the utricular substance; and it owes, we believe, its present name to M. Du Hamel.

81. The cavities which distinguish its construction were called indifferently bags or bladders, pores, and cells, by Grew; by Malpighi, utricles; by others, Elementary vesicles; and more commonly cells. The form of these cells varies so much, not only in different plants, but in different parts of the same plant, as to have authorized, in some degree, these different appellations. The tissue which they constitute, enters into the composition of every organ in the more perfect plants. Of many herbaceous plants it forms the chief portion, and some of the lower tribes of vegetables are said to be wholly composed of it; in other words, no vessels can be actually demonstrated in them. In most cases, it contributes greatly to modify the form of organs, and adds always to their bulk and strength. Nothing can exceed the diversity of appearance in figure, bulk, and texture, which it exhibits in the several parts, circumstances, and conditions in which it is placed. It represents sometimes a lax cellular substance, all the parts of which are succulent and transparent; in other instances, it is compressed into a solid opaque body, retaining but faint traces of its former cellularity; and in others again it is spread out into a most thin and delicate membrane, in which the cellular character is wholly lost. It everywhere envelopes and holds together the vascular system, and seems to be the general receptacle of almost all the vegetable secretions.

82. The figure of the component cells of this tissue is exceedingly various. Sometimes they have nearly a globular or spheroidal shape; in other instances, they are angular, and exhibit, in their section, a greater or lesser number of sides and angles, being in a few examples triangular; in others, square, but more commonly hexagonal; the figure which collections of soft cells, mutually impressing each other, seem naturally disposed to assume. This form is represented in the transverse section of cells, fig. 20. A, Plate XV.; they seem, in this figure, and in most of those given in different works, to possess double sides; but as M. Kieser has remarked (Mém. sur l'Organisation des Plantes, p. 91.), this appearance is produced by the borders of the subjacent cells being seen through the transparent sides of the superior layer. In Plate XVI., fig. 22, is a representation of a transverse slice of the cellular part of Sugar-cane, drawn from nature, and so thin as to exhibit only one layer of cells, in which the sides appear distinctly single; but, in a thicker slice of the same plant, fig. 23, comprehending more than one layer, the double appearance becomes very evident.

83. The size of the cells varies not less than their figure in different plants, and in different parts of the same plant. In one of the plates of Grew, they are represented as possessing twenty different sizes, from that of a minute pore, to the size of a common pea; Hooke examined them in Cork, and in the pith of many plants. In Cork, he reckoned several lines of these cells, or pores, as he calls them, and found there were about sixty placed endwise in one-eighteenth part of an inch, or somewhat more than a thousand in the length of an inch; and, therefore, in a square inch above a million, and in a cubic inch above 1200 millions. (Micrographia, p. 114.) In this substance, the cells are not visible by the naked eye, but become very distinct when highly magnified. In most plants, however, they are readily visible, and their appearance is familiar to every one.

84. When viewed in a longitudinal section, their hexagonal form is much less distinct, and is sometimes wholly lost. In fig. 24, Plate XVI. is a series of single columns of the cells of sugar-cane, in which each cell is, to appearance, bounded only by four sides. Similar representations are given by Hooke of the cells in Cork, and by Kieser, in most of the figures which exhibit longitudinal sections of the cellular tissue: but, in some instances, the hexagonal form is visible even in these sections. In fig. 25. of the same plate, we have given, in outline, the appearance of two series of columns of these transparent cells, in which one series is seen behind the other, and gives somewhat of the confused double appearance exhibited in the transverse section, fig. 23.

85. The nature of the matter contained in the cells of this tissue, varies according to the part in which it exists, and the peculiar powers of the plant. Both Hooke and Grew remarked, that, in the pith and bark of succulent plants, the cells were often filled with aqueous juices, and in the same plants, at other periods, they appeared empty, or filled only with air. In the seed, the cells of the cotyledons contain minute unorganized particles which, at a future period, serve as nutriment for the young plantule. Other particles of still smaller size, of a resinous nature, and a green colour, exist in other parts of this tissue, and bestow on the plant its verdure. In every part of the plant, these cells are also the occasional receptacles of the peculiar fluids which both the sup-vessels and the proper vessels convey; and hence various gummy and resinous substances, corresponding in quality to the fluids previously existing in the vascular system, are frequently detected in them. In the pulp of fruits, the various acid, saccharine, and austere juices that we meet with, are contained in different modifications of this tissue; and it is into its cells that the osseous secretions, which constitute their shells and stones, are made. These facts prove not only the great importance of this tissue in the construction of the vegetable organs, but the active share it bears in the economy of their functions, and demonstrate likewise an universal communication betwixt the vessels and the cells.

86. The sides of these cells, when emptied of their contents, and viewed through the microscope, appear to be formed by a very fine transparent membrane, which some maintain to be everywhere entire, and others to be perforated with pores. The same sources of error exist here as before noticed in similar microscopical observations on the vascular system; and, accordingly, the respective disputants maintain, with equal confidence, the same opinions with regard to the porosity or non-porosity of the cells, as they had previously held concerning the vessels. We must therefore call in the aid of other means besides those of the microscope, for determining the important fact, whether the cells have or have not any direct communication with each other.

87. Dr. Hooke examined the films or sides of the cells of Cork, of the pith of Elder, and of many other plants, with the very purpose of discovering Elementary whether any direct communication existed between organs; but "each cavern or cell," says he, "is distinctly separate from the rest, without any kind of hole in the encompassing films;" nor could he, with his microscope, nor by his breath, nor by any other way that he tried, "discover a passage out of one of those cavities into another." (Micrographia, p. 116.) Dr Grew describes the little cells or bladders that compose the bark of roots, as possessing a spheroidal shape in most plants. When viewed with the microscope, their sides are as transparent as water; and "none of them," he adds, "are visibly pervious from one into another, but each is bounded within itself." (Anat. of Plants, p. 64.) Both Hooke and Grew, however, believed a communication to exist between the cells, from the fact of their containing liquor; and Malpighi held the same opinion from similar considerations; but they nowhere describe the mode or structure by which they conceived it to be accomplished.

88. Later writers have not only adopted this opinion, but professed to demonstrate the structure by which the communication is maintained. M. Mirbel describes the sides of the cells as composed of an extremely thin, colourless, and transparent membrane, which is commonly perforated with pores, the diameter of whose aperture is not, perhaps, the 800th part of a millimetre. These pores are ranged generally in transverse series, and through them, it is said, the cellular tissue both receives fluids from the vessels, and transmits them very slowly through its cells. (Exposit. de la Théorie, &c. p. 105.) M. Sprengel, and some others, adopt this view of the porosity of the cells; but it is denied by Link, Treviranus, and Kieser. The latter author declares, that, "notwithstanding all that has been said concerning the pores in the sides of the cells, his observations, made with the greatest care and exactness, have not enabled him to discover the slightest trace of them." The sides of the cells, he adds, are always formed by a membrane extremely thin, but altogether smooth and uniform; and "the cells themselves have never an open communication with each other." (Kieser sur l'Organisation des Plantes, p. 94.) In a critique on M. Mirbel's doctrine, he farther observes, that, although possessing eyes extremely piercing for microscopical objects, and employing the highest magnifying powers, he has never been able to discern, in the membrane of the cells, the existence of pores, though he sought for them with the greatest care and precaution." (Ibid. p. 29.)

89. From the results, therefore, of direct experiments employed to discover the porosity of the cells, as well as from the combined reports of the most accurate microscopical observers, we must pronounce against the opinions of M. Mirbel; and although he has delineated the form and position of the pores, computed their number, and even measured their apertures, it may, we think, be asserted, that he has either been deceived himself, or has exhibited, as real copies of nature, forms and structures which never had existence but in his own imagination. This charge seems accordingly to have been preferred by some of his opponents; and, in the preliminary observation to the explication of the figures in his last work, he comes forward with this reply to it: "Pour éviter désormais toute espèce d'équivoque, je dois prévenir que les parties que je nomme organes élémentaires, ne se présentent jamais isolément dans la Nature. Je fais donc ici ce que j'ai fait dans mes descriptions; je divise par une opération de la pensée, ce que la Nature n'offre que réuni; et je montre, non pas rigoureusement ce qu'on peut voir, mais ce que la réflexion, guidée par l'observation et l'expérience, présente à l'esprit. N'est-ce pas là le résultat de l'analyse philosophique?" (Exposition, p. 114.) He exclaims! We answer, that, in cases of this sort, we want the fair transcript of the object itself, and not the analytical result of the author's speculations about it; and we hold it not only unphilosophical, but something worse, knowingly to have given, as faithful copies of Nature, representations of the elementary organs, which, as M. Kieser remarks, are designed not from Nature, but from imagination. (Mém. sur l'Organisation des Plantes, p. 77.)

90. If, then, no pores exist in the sides of the cells Mode of for the reception and transmission of the fluids they contain, some other means must be provided for the accomplishment of these objects. M. Link, accordingly, supposes the juices to pass from one cell to another by transudation through invisible pores in their sides,—a supposition which will scarcely be admitted by physiologists as applicable to living organized textures. And M. Rudolphi suggests the still more extravagant opinion, that a decomposition of the fluid is effected by the cells themselves, during which it is transmitted through their sides. (Mirbel's Exposition, &c. p. 183.) To us there occur no other means of accomplishing these operations, consistently with the integrity of the cellular structure, than the exercise of those alternate functions of secretion and absorption, which, from so many other considerations, we have supposed to be carried on in every living part of the vegetable system.

91. Another question of less improtance in relation to the sides of the cells is, whether they are Cells single or double; that is, whether each cell has a side of its own, or whether one side is in every position common to two cells. Mirbel asserts the former, and Kieser maintains the latter opinion. In fig. 20. B. Plate XV. is an outline representation of these double sides as given by Kieser. From the extreme thinness of the membrane, it is very difficult, he says, to distinguish this double structure; but where the cells are large, and a glass that magnifies highly is employed, each partition that separates two cells is distinctly seen to be composed of two membranes, which are sometimes separated about the middle of the partition, and united towards the angular points. (Mém. sur l'Organisation des Plantes, p. 91.) The existence of this double structure receives some countenance from the fact lately observed in the construction of the honeycomb by Dr Barclay, who says that each side of every cell in the comb is composed of two plates, or is double. (Wernerian Transactions, Vol. II.) It may still, however, be more properly said, that each side of every cell is truly single, and is rendered double only by coming into contact with the corresponding side of an adjacent cell. 92. When the cells have a regular hexagonal figure, and are equally distended with their appropriate juices, there is no reason to suppose that any vacuities are left between their sides or angles. Mathematicians have long since demonstrated a regular hexagon to be one of those figures that completely fills up a given space; and that no vacuities can exist either about its sides or its angles. Where, however, the cells deviate from this regular figure, and more or less approach to a spherical form, vacuities or interstices may readily be conceived to occur. These vacuities are said to have been first noticed by Leuwenhoeck, and afterwards by M. Treviranus, who describes them as interstices left between the cells in their mutual approximations towards each other: He gave them the name of *intercellular canals*, and considers them as the only passages by which the fluids can be conveyed through the cellular tissue. (*Kieser's Mém. sur l'Organisation des Plantes*, p. 20.)

93. On the other hand, MM. Mirbel and Rudolph, altogether deny their existence; but M. Kieser contends strenuously for it. He describes them as small interstices situated at the angles of the hexagonal cells, and formed not by any sides of their own, but by the mutual approach of three contiguous cells, and possessing, therefore, a prismatic form. These interstices, he conceives to exist at every angle, and thus every cell to be surrounded by them. In fig. 20, B, Plate XV., the black angular points denote their place. By their conjunction with each other, they form a canal, which, when the hexagonal figure is perfect, and the cells are ranged horizontally, extends both in a longitudinal and transverse direction; and when the cells are placed obliquely, then the canals have a similar direction. Their size varies according to that of the cells, by the sides of which they are constructed; they contain and convey the proper juices in the bark, but in the pith are often dry; and their course is said to terminate only with that of the cells themselves, at the surface of the plant. (*Mém. sur l'Organisation des Plantes*, p. 104.) Such are the organs which, as we have seen, M. Kieser considers to convey both the sap and the proper juices in plants; and which he describes as produced universally by that form of cell, which, of all others, is most calculated to exclude their existence. That, in some circumstances they may exist, and become reservoirs of the sap, or other juices, seems highly probable; but of the absurdity of ascribing to such casual productions, the performance of the primary functions of the vegetable system, we have already spoken.

94. The cellular tissue, as described above, is that form of it which must be regarded as the most perfect. From various causes, however, it is subject to great alterations. In herbs, and in the pith and succulent parts of trees, the cells preserve their original form and appearance for a considerable time; but, by the growth of the other parts, and consequent extension and compression they experience, they acquire in the bark and wood an elongated figure, and this both in a transverse and longitudinal direction. In the latter case, they surround and connect the layers of vessels with each other, constituting what has been named the *parenchyme* of the bark and wood. In this form, their size is often greatly reduced, their cavities sometimes obliterated, and their cellular character altogether effaced. In other instances, traces of a cellular structure are occasionally visible, appearing in detached portions among the perpendicular vessels. In plants of very rapid growth, the cells are said by Kieser to become elongated in a longitudinal direction, and yet preserve their capacity nearly unchanged; so that the tissue which they form appears as if composed of a number of small cylinders. It was probably this construction that led Malpighi to regard sometimes as vessels, what, in reality, appear to be only a collection of these elongated cells. His error appears, however, but slight, compared with that of M. Kieser, who considers the bark as altogether constructed of these elongated cells, somehow metamorphosed into cortical fibres, and interlaced by other similar cells extending in a transverse direction. The wood, too, he supposes to differ in construction from the bark only in possessing spiral vessels; its ligneous fibres he farther holds to be formed by the sides of the aforesaid elongated cells, where the intercellular canals have disappeared; and, as the spiral vessels, according to him, convey only air, no other organs remain for performing the office of sap-vessels but the intercellular canals. (*Mém. sur l'Organisation des Plantes*, p. 99, 101.) But there is a wide difference between the observations and the opinions of M. Kieser;—the former we regard generally as laborious, minute, and faithful;—the latter often appear to us crude, inconsistent, and absurd.

95. From suffering compression in a transverse direction, the cells have frequently their longer diameter thrown into that position, and thus extend from the centre to the circumference of the plant. This disposition, as will afterwards be shown, was fully noticed by Grew and Malpighi. Leuwenhoeck also observed it, but mistook the cells, as Malpighi had done, in the opposite direction, for vessels, and considered their partitions as valves—errors which M. Kieser, as well as others, duly points out, and yet, as we have just shown, similar to that into which he himself has fallen. In this transverse direction, the tissue forms partitions more or less large between the vessels, as will afterwards be shown, and by the obliteration of its cells, it is frequently reduced to the condition of a solid membrane.

96. Beside these more constant and necessary changes in the figure and character of the cellular tissue, it often suffers others of a more casual and accidental nature. In the pith, as the plant grows up, divers ruptures, says Grew, occur, oftentimes very regularly, and observed constantly in the same species of plant; these ruptures are sometimes prolonged, so as to form a tube of considerable length. (*Grew's Anatomy of Plants*, p. 120.) Others have observed similar canals in the pith, formed not by sides of their own, but by those of the adjacent cells, and very various in size and form: they have been called *lacunae* or reservoirs, contain a variety of substances, and sometimes, especially in aquatic plants, only air. As we have seen the cavities of the larger spiral vessels to be filled with vesicles, so the larger cells of the pith, according to Grew, frequently con- Elementary tain smaller ones, or are divided by cross membranes.

A similar observation is made by Kieser, who likewise remarks, that, in the empty cells of Calla Æthiopicæ, he has sometimes seen small round-headed bodies, supported on little peduncles, which spring from the sides, and point towards the centre of the cells. Small crystallized bodies are also occasionally found in the cavities of the cells, and within the intercellular canals. (Mém. sur l'Organisat. des Plantes, p. 94.) Of those changes in the character of the cellular tissue, by which its cells are converted into receptacles and reservoirs of the proper juices of the plant, we before discoursed when treating of the proper vessels. To such an extent does this change sometimes proceed, that, in aged Oaks, and, according to Kieser, in Guiacum, and probably in many other plants, the whole cellular tissue becomes filled with these secreted matters, and the distinctive characters of the cells, and almost of the vessels themselves, are obliterated and lost.

ARTICLE II.

Of the Structure and Formation of the Cellular Tissue.

But anatomists have not confined themselves solely to descriptions of the more obvious forms and characters of this tissue: they have attempted to penetrate into the secret of its ultimate structure, and, deserting thus the beaten path of observation and of sense, have wandered at large through the regions of imagination. It would be a waste of time to pursue, to any considerable extent, these vagaries of the fancy; but a brief notice of a few of them may afford some amusement, and perhaps instruction, to the reader.

It seems pretty generally admitted, that the tissue, of which the cells are constructed, partakes of a membranous nature; and the first question therefore is, of what materials is this membrane composed? Grew considered the cells, as well as the vessels, to be formed of exceedingly minute fibres, which were themselves tubulous, or rather smaller vessels. (Anatomy of Plants, p. 76, 77.) Malpighi deemed the thin membrane that forms the cell to be produced from an effused juice, that gradually acquired solidity, and was everywhere furnished with a reticulation of vessels. (Anat. Plantar. p. 29.) According to Du Hamel, the constituent part of this membranous structure is rather to be regarded as filamentous than vascular; though he admits, that, in fleshy fruits the vessels of the cellular tissue are so numerous that they seem to form the cells themselves. (Phys. des Arbres, Tom. I. p. 15, 24.) In the leaf, the elder De Saussure maintained, that what is called the cellular part is formed entirely of minute transparent vessels, which, between their junctions, swell out so as to give the appearance of cells or vesicles, though in reality they are a net-work of vessels. (Encyclop. Method. Tom. I. Art. Parenchyme.)

The manner in which these primitive vessels or filaments have been employed to form the membrane, has likewise been differently conceived by different writers. Grew imagined them to be disposed in opposite directions, like the warp and woof of the weaver's cloth, and everywhere knit together by the Elementary weftage of other fibres. Du Hamel could see no such regular structure, and therefore believed them to be united promiscuously, like the filaments in a piece of felt; and Malpighi and Saussure seem to have regarded them as joined together in the form of net-work.

Not less different have been the modes in which this membranous substance, during or after its formation, has been supposed to acquire its cellular figure. Grew seems to have thought that the figure of the cells was determined by the course which the vessels pursued in their formation; hence he remarks, that while the vessels proceed circularly, and keep within the compass of the cells, the cells are round; but where they wind out of one cell into another, then an angular form is produced. (Anatomy of Plants, p. 77.) Later observation, however, has rendered it probable that the angular form is the result rather of the mutual pressure which the cells subsequently exert on one another, than communicated during their formation. The general appearance which a mass of cells exhibited after their formation, he resembled to that of the froth of beer (Ibid. p. 67.); but never, as some seem to have supposed, imagined them to be produced by a similar operation. By all those who maintain the vascular nature of the cellular tissue, the cells must be considered as originating from the vessels—an opinion frequently advanced by Malpighi, who particularly describes the excrecence on the leaf of the Oak, called gall-nut, as composed of a cellular structure, which is derived immediately from the vessels of the leaf, and which opinion, as he justly remarks, the structure of the leaf itself, of the flower, and the fruit, hereafter to be described, will illustrate and confirm.

A different view of the origin and formation of cells has been taken by others. Ludwig conceived the vessels, as well as the cells, to derive their origin from a common membrane, but does not describe the manner in which the cells and vessels could be produced out of it. (Institut. Phys. Regni Végétab.) This opinion has since been adopted by Mirbel, who considers it as perfectly original; and of Mirbel has gone more into detail regarding the mode in which cells and vessels are produced. According to him, the entire mass of the vegetable is a membranous tissue, the ultimate structure of which he does not pretend to explain; and out of this tissue the small cavities called cells, and the vessels are alike formed. He of course denies the independent existence of cells and vessels, and of the vascular productions or fibres by which these two organs have, by others, been supposed to be united: and maintains that the entire vegetable is constructed of one continuous membrane, between all the parts of which a communication is kept up by means of innumerable pores. (Exposit. de la Théorie de l'Organisat. Végét. p. 60, 62, 279.) How this membrane acquires the varied and regular forms which it exhibits in the cells and vessels of the plant, we are not distinctly told. All that we can discover on this point, is, that the cells are not distinct sacs or utricles, but produced out of a membrane which unfolds itself (se dédouble) in some inconceivable manner, so as to leave empty Elementary spaces contiguous to one another, which constitute Organs of the cells. (Traité d'Anat. et Physiol. Vég. Tom. I. p. 56.) The mass of cells thus formed, is considered very similar to the vesicles of the froth of beer, with which Grew had previously compared it; for the thin transparent plates of these vesicles are said to be everywhere continuous, and each side to be common to two vesicles, while all interstices or intercellular spaces, and all connecting vessels and fibres, are completely excluded. We are also told that the smaller vessels are only elongated cells, and the larger ones cavities formed in the cellular tissue; so that this tissue must be regarded as the essential organ of vegetables, and the other organs are but modifications of it; and in this way M. Mirbel passes off the assertion of an opinion for an explanation of the mode in which the vessels are constructed.

102. Instead of the continuous mass of cells which Mirbel professes to describe, M. Sprengel conceives the cells of this tissue to originate from elementary globules, such as are found in the cotyledon of the bean, which at first seem a chaotic mass of extremely minute vesicles, but are gradually developed, and acquire an angular form. This seems likewise to be the opinion of M. Treviranus, who regards the cells as originating from the aforesaid cotyledonous vesicles, which have at first a round form, but are changed afterward by the effect of pressure; these vesicles are supposed gradually to extend, to close towards each other, and in this way to construct the tissue. The elementary vesicles, however, out of which these writers construct their cells, are justly regarded by M. Link (Kieser's Mém. sur l'Organisation des Plantes, p. 17, 19, 23,) as globules of starch deposited for the future nutriment of the embryo.

103. M. Kieser also derives the origin of the cells from primitive globules, but looks for them in a different part of the vegetable system. In the proper juices of plants, certain minute particles or globules have been observed, which, according to this author, are the rudiments of future cells, or rather, says he, true cells themselves, though extremely minute. An infinite number of these globules exist in the proper juices, which juices are present in every primitive utricle. Gradually these globules dilate, approach, and are soldered to each other, receiving by their reciprocal pressure an hexagonal figure, and thus constructing the cellular tissue, which is nothing but a parenchyme of many small cells, enclosed in a great cell, or primitive utricle. Each cell, therefore, of the cellular tissue is, in its origin, only a transparent globule, which becomes filled with fluids, and soldered to the adjoining cells, so as to form an entire piece, the parenchyme of the plant. As this dilatation of these primitive globules is, in all cases, the first function of the plant, the cellular tissue is the first and primitive organization of the plant, from which proceed afterwards all the other elementary organs. (Ibid. p. 219.) Such is M. Kieser's account of the origin of the cellular tissue, which, as we think, surpasses in absurdity that of M. Mirbel, whose doctrine he so justly condemns;—but so much easier is it to "see the mote in our brother's eye," than to be conscious of the "beam in our own."

CHAP. II.

THE ANATOMY IN GENERAL OF THE COMMON TEXTURES OF VEGETABLES.

Preliminary Observations.

104. The elementary organs, whose description Nature has so long occupied our attention, form, either singly or by their combination, all the other parts of plants. Some of the lower tribes of vegetables consist entirely of cellular tissue, in which no vessels are at any period to be seen; and, even in the higher orders, many parts exhibit no appearance of a vascular structure. There can be little doubt, however, of the existence of such a structure, since, physiologically speaking, we can form no just conception of the growth of an organized body, without associating with it the existence of a vascular system. In all plants, the pith consists of cellular tissue alone. In herbaceous plants, this tissue forms their greater portion; but in trees, the number of vessels is so great, as to constitute the chief bulk of the plant. To certain forms of these elementary organs, whether existing singly or in combination, we have given the name of common textures, because they are very generally to be found in all plants, and in almost all parts of them, howsoever varied in quantity, proportion, and arrangement. These textures are familiarly known under the names of Cuticle or Skin, of Bark, of Wood, and of Pith; to which may be assigned the general appellations of the Cuticular, the Cortical, the Ligneous, and Medullary textures.

105. All the several textures just enumerated, are readily distinguished, by their different places and characters, in the section of most arborescent plants, in which they commonly appear well defined, and perfectly distinct from each other. In many plants, however, both herbs and trees, this distinction of parts is not preserved; but, with the exception of the cuticle, all the other textures are blended together through the entire substance of the plant, as was long since noticed both by Malpighi and Grew. "In the stalk of maize or Indian wheat," says Grew, "the work of nature appears less diversified; in which, although there are the same parenchy mous and ligneous parts, as in all other plants, yet is there neither bark nor pith, the vessels being dispersed and mixed with the parenchyma, from the circumference to the centre of the stalk." "The like structure," he adds, "may also be seen in the Sugar-cane, and some other plants." (Anat. of Plants, p. 104.) Similar observations were made by Malpighi, not only on different species of wheat and sugar-cane, but on ferns and palms. "In Ferns," says he, "the vascular fasciculi are numerous, but placed without order, and are everywhere sustained by the intervening cellular tissue, the cells of which are sometimes much smaller than the orifices of the vessels themselves." (Anat. Plantar. p. 24, 25.) This structure is represented in the transverse section of the sugar-cane, Plate XVI. fig. 26.; and in a similar section of the palm, fig. 28. of the same Plate. 106. This variety of structure, thus clearly described, and distinctly delineated in the works of Malpighi and Grew, has lately been noticed by M. Desfontaines, who deems it common and peculiar to all plants, whose seeds have but one lobe or cotyledon; while all plants produced from seeds that have two cotyledons, are held to possess a very different arrangement of parts. Vegetables, according to him, may be distinguished into two divisions: 1st, Those which have no distinct concentric layers, whose solidity decreases from the circumference towards the centre, and whose pith is interposed among the vessels, and does not extend in divergent rays. 2d, Vegetables which have distinct concentric layers, whose solidity decreases from the centre towards the circumference, and whose pith is contained in a longitudinal canal, and extends in divergent rays. The former structure he considers as peculiar to plants, whose seeds are monocotyledonous, and the latter as belonging to those which have dicotyledonous seeds. (Mém. de l'Institut. Nat. Tom. I. p. 478.)

107. There does not, however, appear any just ground for this supposed coincidence of structure betwixt the seed and the stem. That many plants which spring from monocotyledonous seeds, are destitute of concentric layers, and have no distinct bark or pith, is most certain; but it is not less certain that many herbaceous plants, which are produced from dicotyledonous seeds, are pretty much in the same condition, being equally destitute of concentric layers, and of divergent rays; and in which the bark and the pith must be regarded as one continuous structure. On the other hand, some monocotyledonous plants, as M. Desfontaines admits, may deviate a little from the prescribed conditions. In a paper on the organization of such plants, M. Mirbel, who regards this doctrine as the most important step made of late years in Vegetable Anatomy, says, nevertheless, it would be erroneous to assert that they have never a bark. In several species of plants, he produces examples to the contrary; and adds, that, in some instances, their diametral growth goes on at the circumference, which would seem to approximate them to dicotyledons. As, however, there is no appearance of divergent rays, or of concentric layers, these examples are considered by him rather to confirm than overturn the theory of M. Desfontaines. (Annales du Mus. d'Hist. Nat. Tom. XIII. p. 67.) But if, in this theory, its second division embrace only those plants in which the concentric layers are perfect, and divergent rays exist, then it excludes a great number of herbaceous plants, whose seeds have two cotyledons; and if the absence of these regular layers, and of divergent rays, serve as a passport to the first division, then many of these same plants must be admitted among those whose seeds have but one cotyledon. The theory of M. Desfontaines, therefore, rests on too partial an observation of the structure of plants. All that is true in it was previously known, and all that is new will not serve the purpose of its author. For the former part, he has omitted to do justice where it was due; for the latter, he has received extravagant praise where it has not been deserved. It has been our wish to render equal justice to all.

108. Instead, therefore, of seeking to found the structure of the stem on the form of the seed, it will be more correct to describe the several varieties of its appearance, as they actually present themselves on dissection; beginning, as Grew and Malpighi have done, with the more simple arrangement of the elementary organs, as they occur in certain plants, and following them, through their several gradations, to more precise and better defined forms. Although some of these plants do not, properly speaking, possess either distinct bark or pith, yet no misapprehension can arise from treating of these parts under the denomination of common textures; for though not universally, they are very generally present; and even where they are not, the descriptions will, with little variation, apply to such structures. As of these common textures, the pith is the most simple, we shall commence our account of them with a brief description of it.

Section I.

Of the Pith or Medullary Texture.

109. The pith (medulla) of plants when present, occupies the centre of the stem, where it is commonly surrounded by a circle of vessels which construct for it an appropriate canal. In the succulent shoots of trees, its proportion to the other parts is generally large; but it diminishes as the tree advances in age, and is frequently entirely obliterated. Where the vessels of the wood are few in number, as in herbs, only a few fasciculi are seen to surround the pith, and the intervening spaces are occupied by a boundary of thickened cellular tissue. In some plants again, no pith whatever exists, but the stem is hollow or tubular. In other instances, and especially in roots, the centre of the stem is occupied by vessels; and in others, both cells and vessels, promiscuously blended together, constitute the centre of the stem.

110. In those plants where the pith is present, and possesses its most perfect form, it is seen to be composed entirely of cellular tissue, possessing often very different shades of colour, but, in its anatomical characters, resembling exactly the description already given of that tissue. Its bulk, in different plants, is exceedingly different, as are also the form and size of its cells. It is frequently entirely insulated by the surrounding vessels, but is often continuous with the cellular tissue of the bark. Its cells contain, especially in the early age of the plant, aqueous fluids which afterwards disappear, and then the cells become filled only with air. The proper juices of the plant may also be sometimes detected in the cells of the pith. Of the ruptures produced in it by desiccation and other causes, we have already spoken in discoursing of the cellular tissue; they occur particularly in succulent plants, where the cells are large, and their sides thin; so that, as the plant advances to maturity, the pith breaks and shrinks up, making the trunk a pipe. (Grew's Anatomy of Plants, p. 129.) We have also noticed the fact, that, within the cavities of the larger cells of the pith, new vesicular productions are sometimes found. 111. Grew speaks of the existence of vessels in the pith of certain plants, as in that of the Fig and the Pine; but he adds, that they are usually so postured as to form a ring about its margin. (Anatomy of Plants, p. 119.) They are doubtless to be considered as enlarged proper vessels, which made a part of the first ligneous circle, and have retained therefore nearly the situation in which they were originally formed. Hence, as he observes, they are of divers kinds, answerable to those of the bark, containing, in the Fig, a milky juice, and in the Pine, a resinous substance. Similar vessels, containing a proper juice, were observed also in the pith of Elder by Malpighi, who seems to regard such appearances as common, where the contained juice concretes, or possesses a dark colour. (Anat. Plantar. p. 4.) It is probable, however, that the organs here considered to be vessels, may, in some cases, be cells, into which these juices have been poured; but where real vessels of this kind are found, they are not to be considered as a part of the original structure of the pith; but occurring only in consequence of the changes, which the vegetable body undergoes in the progress of its growth.

112. The general nature of the pith is thus clearly announced by Grew. "Although," says he, "it have a different name from the parenchyma in the bark and the insertions in the wood, yet, as to its substance, it is the very same with them both; whereof there is a double evidence, viz. their continuity, and the sameness of their texture;" so that all these parts are "one entire piece of work, being only filled up, in divers manners, with the vessels." (Anat. of Plants, p. 119.) This continuity of the pith with the cellular tissue of the bark, by means of the insertions or transverse ranges of utriculi, as he calls them, is also adduced by Malpighi as evidence of the similarity of their nature, and of the pith being, as it were, an intercepted portion of the bark (Anat. Plantar. p. 4—30); an opinion which seems abundantly confirmed by the intermixture of the medullary and cortical textures in many plants, in which, as already remarked, the distinctive characters of bark and pith are alike lost, and the entire stem exhibits only one uniform appearance of structure.

113. The term medulla, employed by the ancients to denote this texture, derived its origin, no doubt, from the resemblance which the pith, in the centre of trees, bore to the marrow in the bones of animals; and as the same term, in Animal anatomy, was incorrectly employed to express alike the marrow in the bones, and the nervous substance in the vertebral column, so the same latitude of signification has been extended to the vegetable system. Hence, as Malpighi remarks, the medulla in vegetables was regarded as analogous, in its nature, to the brain of animals, a doctrine which even later writers have continued to espouse. It is not our present intention to describe the uses of the pith, but only to remove erroneous opinions concerning its nature, and restore to it that just anatomical character, long since assigned it by Malpighi and Grew; and which some writers have of late put forth as a considerable novelty.

Section II.

Of the Wood or Ligneous Texture.

114. Immediately surrounding and enveloping the pith, is the part called the wood (lignum vel lignea portio of Malpighi.) It is essentially composed of vessels and of cellular tissue, but combined in such an infinite variety of proportions, and exhibiting such a boundless diversity of forms, that it is difficult to seize even its more general features, without the risk of extending our descriptions beyond the limits which our plan necessarily prescribes.

115. Except in those vegetables in which no vessels have been hitherto demonstrated, but in which they must nevertheless be presumed to exist, this texture may be considered to form a part not only of every plant, but of all its organs; for into whatever part fluids are conveyed, vessels must be supposed to extend; and wherever vessels are present, cellular tissue is to be found; hence, in its distribution, it may be considered the most universal of all the textures. In trees, the vessels, as we have frequently remarked, are very numerous, and, when viewed in a transverse section, are seen to be disposed in layers or concentric circles around the axis, and to stand also in lines or radii, diverging from the centre of the tree. See fig. 4. Plate XVII. Between each line or ray of vessels, a thin partition of cellular tissue is interposed, which extends in the direction of the ray, through the entire substance of the wood. At certain distances, varying in different trees, thicker transverse portions of the same substance are placed, and are readily distinguishable in almost every species of wood. Between each layer that is annually added to the wood, and each of the smaller layers that go to the formation of the larger one, cellular tissue seems also in some trees to be longitudinally interposed; so that it is probable, that, in both directions, each fasciculus of vessels is intercepted by cellular tissue, and that in such trees no two fasciculi are on any side in immediate contact with each other. It is even probable, that the individual vessels which contribute to form the fasciculi, are themselves connected by intervening cellular tissue, which acts like the neurilema that holds together the filaments of the fasciculi in the nerves, or the cellular substance that connects the primary filaments in the muscular fibres of animals. In this manner, the whole vascular system of the plant is everywhere connected and held together by cellular tissue. Of this tissue, and the different figures its cells acquire, from the different modes and degrees of compression to which they are exposed, we have already spoken.

116. In many trees, however, as Palms, the vascular fasciculi, though numerous, are much less abundant than in the examples just referred to. They are consequently placed at a greater distance from each other, and, not being disposed in regular lines, do not constitute that radiant appearance so common in ordinary trees, but are promiscuously dispersed through the cellular tissue. See fig. 28. Plate XVI. As this tissue itself is not, from the same causes, compressed either in the direction or to the extent before described, the smaller membranous partitions that divide the vascular radii from each

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other are not produced; neither, for similar reasons, is there any distinct appearance of the larger partitions, that, at certain distances, intersect the diameter of other trees. The cellular tissue, therefore, in such plants, retains more of its primitive character, and appears everywhere to surround the vascular fasciculi, but nowhere to be so compressed as to form solid partitions between them. In some plants which possess this structure, as the Sugar-cane (fig. 26, Plate XVI.), the cells indeed retain their perfect forms, and even the fasciculi of vessels, though standing at considerable distances from each other, have towards the centre of the plant a symmetrical arrangement. This latter circumstance is observable in many other plants, which have even fewer vessels than the Sugar-cane; so that it is probable, that, in the first instance, it takes place in all; and that the irregular position of the vessels in the Palm and similar trees, particularly towards their circumference, proceeds from the peculiar modes of their growth, and are not a primary condition of their structure. This intermixture of the vessels and cells in the plants now under consideration, extends from the circumference to the centre, so as to constitute their entire bulk, to the exclusion of bark and pith; unless we choose rather to say, that, in such plants, the medullary, ligneous, and cortical textures, are all blended together.

117. In other examples, the vessels form a still smaller portion of the ligneous texture, consisting only of a few fasciculi, which stand at considerable distances from each other, the intervening spaces being occupied by cellular tissue, which forms the chief bulk of the plant. See fig. 32, Plate XVI. Though few in number, the vessels, however, are symmetrically disposed, and, in the same species, preserve always the same position, the fasciculi being placed at the same relative distance from each other, and from the common centre of the pith. Sometimes, instead of a few solitary fasciculi, they consist of several ranges, forming an imperfect sort of concentric layers, and in such examples, the ligneous texture is commonly separated by distinct but irregular marks from the two other textures. In these plants, the cellular tissue preserves its characters, and exhibits no appearance of divergent rays.

118. The three modes of arrangement above described, appear to constitute the chief varieties of structure in the ligneous texture; but in each variety, and through every stage by which they graduate into one another, the greatest diversity of forms prevails. Each species of plant has its peculiar internal structure, as well as its external form; and this seems to be in a great measure determined by the number of vessels that enter into its composition, and their peculiar mode of arrangement. If the vessels are few, the cellular tissue is large in proportion, and its characters are distinct and well preserved—if they are numerous, and disposed in rays, the tissue is compressed in various directions, loses more or less completely its cellular character, and forms alike those divergent rays, or transverse partitions already so often noticed, and those thin membranous expansions, or fasciae, which, both in the bark and wood, are seen sometimes to cover the vessels in a longitudinal direction.

119. The manner, too, or rather the place, in which the vessels are developed, in perennial plants, will greatly contribute to vary the appearance of the ligneous texture. In those trees, whose diameter is annually increased by the formation of new vessels around the cylinder of older wood, the new parts must necessarily present in their longitudinal section the appearance of annular layers superimposed on one another, and, in their transverse section, that of concentric circles; but in Palms and similar trees, where the development of new parts seems to be accomplished in a different manner, their appearance, under similar sections, may be expected to be different.

120. In a longitudinal section of the Palm, says M. Desfontaines, we discover an assemblage of large ligneous fibres (that is, vascular fasciculi), solid, smooth, and flexible; and these are composed of others still smaller, which are firmly united together; they mostly run parallel to the axis of the trunk, from the base to the summit, without interruption; but some proceed obliquely, and cross the others at angles more or less sharp. See fig. 29, Plate XVI. In a transverse section of the same stem, continues the author, we remark neither concentric circles, nor transverse partitions; but the fasciculi of vessels placed without order by the side of each other, are enveloped by the cellular tissue, which fills up all the intervals: they sensibly approach each other, harden and diminish in size in proceeding from the centre to the circumference. See fig. 28, Plate XVI. So that the stem has much more strength and solidity near the surface, than in the interior, an organization quite distinct from that of ordinary trees.

121. The cause of this diversity of structure seems to be amply accounted for by the different modes in which the growth of these trees is accomplished. When the seed of a Palm is sown, the leaves, says M. Desfontaines, successively develop and augment in number for four or five years; the neck of the root augments in the same proportion; the bulbous part, formed by the reunion of the petioles of the leaves, increases insensibly; its solidity augments, and at length the stem rises above the earth with all the size it ever acquires. Its figure is cylindrical from the base to the summit, and if the diameter be measured at different epochs, it will be seen, as Kampfer had already remarked, not to increase. The Palm, therefore, is a regular column, whose summit is crowned with leaves, disposed above each other circularly; those which grow in spring shoot always from the top; the older ones, placed below, dry, and when they fall, leave circular impressions, which furrow the surface of the stem, and mark its years until it has ceased to grow.

122. If next we examine the interior, we discover, as M. Desfontaines thinks, the true reason why the stem rises in a column, and does not, like other trees, yearly augment in size. This was done by M. Dau-benton, who states, that every leaf of the Date-palm, in proceeding from the bud, is formed by a prolongation of the vascular fasciculi and cellular tissue which exist in the trunk of the tree, as is apparent in the petiole of the recent leaves, and of the dried ones that adhere to the trunk. The elongation of the trunk is produced, therefore, by the leaves which annually proceed from it; and as the parts which form these leaves, spring from the centre, they always, as they shoot, force the older leaves outwards. Hence, therefore, as the augmentation of these trees originates at the centre, all the parts capable of displacement must be pushed outwards, just as the new layers of bark and wood, formed annually in ordinary trees, force outward the older layers of bark exterior to them.

123. In these latter trees, continues M. Dauben- ton, the recession of the bark has no limits, so long as new parts continue to be formed beneath it; because the new cortical layers are flexible, and the older ones readily break and give way: but in the Palm, the substance of the trunk has more compactness as we approach the circumference, and, at a certain point of density, it no longer yields to the central force of the interior parts; so that, when this point is reached, no farther enlargement takes place; and hence, the Date-palm scarcely exceeds ten inches in diameter. It is for similar reasons that the trunk of the Date-palm is of the same size through its entire length; for, in proportion as the tree rises, the exterior parts of the trunk lose successively their flexibility, and when they have reached a certain degree of density, they no longer yield to the force from within; and as this is equally the case in all parts, the trunk is necessarily of the same size throughout. (Mém. de l'Inst. Nat. Tom. I. p. 482, &c.)

124. It is farther evident, that, in this mode of growth, no appearance of concentric circles, similar to those of ordinary trees, can have place; for, by the growth at the centre, the exterior vessels are continually displaced from their original positions, are more and more compressed as they are forced towards the circumference, and present, in their transverse section, that irregular distribution which they have been described to possess. Hence, the cylindrical figure and the absence of concentric layers are as necessary consequences of the mode of growth in these trees, as the presence of those layers and the conical figure are of the mode of growth in ordinary trees. The greater solidity of the parts at the circumference is clearly to be ascribed to the same cause; and even the want of regular transverse partitions must in part also have a similar origin, and be ascribed, perhaps, in part to the smaller number of vessels which these plants possess, as well as to their irregular distribution.

Section III.

Of the Bark or Cortical Texture.

The Bark.

125. This texture, in its component parts, resembles that of the wood, being made up, like it, of vessels and cellular tissue intimately connected with each other. Its structure, as a distinct texture, is best characterized in the bark of ordinary trees, as it is there separated, in a great measure, from the ligneous texture. As, in these plants, a new layer of vessels is annually made to the wood, so a similar, but much thinner layer, is yearly added to the bark, to which the name of liber has commonly been applied. These vessels are at first strait, and run parallel to the axis of the trunk; but, by the successive formation of new layers beneath them, they are gradually forced outward, become separated more and more from each other, and, touching in a few points only, exhibit at length a reticulated figure (See fig. 18. Plate XV.); the meshes of which yearly augment in size, from the greater space over which they are continually spread.

126. Between the vessels thus annually formed, a considerable portion of cellular tissue is interposed, which, in the young and succulent state of parts, contributes chiefly to the thickness of the bark. This tissue is variously compressed by the vessels, so as to form transverse partitions betwixt them, which, in the Vine, the Oak, and many other trees, as both Grew and Malpighi remarked, are seen to be continuous with those of the wood; and in this way the two textures are united together. In the expressive language of Grew, the bark, therefore, does not merely surround the wood as a scabbard does a sword, or a glove the hand, but is truly continuous with it, as the skin of the body is with the flesh." In the Willow and other trees, when full of sap, the bark is so easily separated that it seems to have no connection with the wood; but this is supposed by Grew to arise merely from the extreme fineness and tenderness of the vessels that are annually formed in that part, and which, on that account, oppose no obstacle to the separation. (Anat. of Plants, p. 129.) It is probable, however, that the cellular tissue forms the only direct connection betwixt the cortical and ligneous textures, and that, if a vascular communication exist, it is only, as in all other cases, through the medium of that tissue.

127. Beside the transverse compression which the cellular tissue experiences from the vessels, it is compressed, in the opposite direction, by the formation of the new layers of bark and wood beneath the older bark. These, in the progress of their growth, exert an expansive force outwards, so that the cells of the tissue are made to assume an oblong or flattened form in the direction of the vessels of the trunk, or sometimes to form a thin fascia upon the vessels, in which the cellular character is nearly or entirely obliterated. It is by the continued exertion of this force, acting on the exterior and desiccated layers, that these latter ultimately crack; producing figures of different sizes, which have frequently the shape of rhombs, the fissures of which represent, according to Grew, the position and track of the vessels in their reticulations. (Anat. of Plants, p. 129.) The spaces or meshes formed by these reticulations, are always filled up by cellular tissue, which, in the opinion of Malpighi, originates from the vessels themselves.

128. Both in the vessels and cells of this texture, Collections of the proper juices frequently occur; especially in plants in which these juices are of a viscid nature, and disposed to concrete; as was before remarked, when treating of the proper vessels. Similar collections of matter, originally existing in the bark, are likewise met with in every layer of wood, and even in the pith of certain trees. It is only in plants in which the proper juices are coloured, or disposed to concrete, that this intermixture of the cortical and ligneous textures has been traced through the whole substance of the tree; but it is probable, from the conjunction of the vessels of the bark and wood at the period of their formation, that it is common to other plants, the nature and properties of whose juices afford no clue to its detection.

129. In most herbaceous plants, the cortical texture is not so clearly distinguished from that of the wood, since in them the greatest variety obtains both in regard to the number and relative position of the sap and proper vessels; and very frequently the cellular tissue is quite continuous, and of uniform appearance through the entire substance of the plant. In general, however, the sap-vessels occupy the inner place, and are surrounded by the proper vessels, disposed either in rings, or distinct fasciculi, more or fewer in number. Sometimes the sap-vessels seem to be placed exterior to the others, and hence it is difficult to discover the true place of the proper vessels in such plants, unless the nature of their juices conduct to it. From the position of the vessels, therefore, it is often difficult to define the boundaries of the cortical and ligneous textures, and for the reason already assigned, the cellular tissue rarely affords much assistance. According, however, to the number and disposition of the vessels, this tissue, even in these plants, suffers a certain degree of compression, so as to form thickened boundaries around the fasciculi, or sometimes large transverse partitions which communicate with those of the wood, in which, though the figure of the cells is more or less altered, the cellular character is usually preserved.

130. In other plants, the intermixture of proper vessels with those that carry sap, seems to be general through the whole plant; and consequently no distinction can be made between the ligneous and cortical textures. In such plants, the proper juices must be considered to exist in every part; and accordingly Malpighi, as we before remarked, points out a vas proprium, or proper vessel, as accompanying every fasciculus of vessels in different species of wheat. (Anat. Plantar. p. 24.) From the similarity of structure in Palms, and especially from their mode of growth, there can be little doubt that a similar intermixture of the two kinds of vessels prevails everywhere in them; and with respect to these plants, what has already been said of the construction of the ligneous texture, is equally applicable to that of the bark.

131. We have thus given a very brief and general view of the principal textures that enter into the construction of plants, and pointed out the more prominent diversities of character and appearance which they exhibit, as well in their simple as in their more complex forms; and as they exist either separately or variously intermingled together. Our descriptions have been confined entirely to the trunk or stem, but, with slight variation, they are applicable equally to the root and branch, in which a similar combination of the elementary organs obtains. In the root, however, they commonly exist in a more compressed and compacted form, so that the ligneous texture is seen chiefly to predominate, frequently to the entire exclusion of the pith; and often, in great part also, to that of the cellular portion of the bark. This is not however universal, especially in annual plants, some of which, as the carrot and others, particularly in a cultivated state, are distinguished by the very large portion of cellular tissue which enters into the construction of the cortical texture. Of the modifications of these several textures, as they exist in leaves and other organs, we shall have occasion to speak when we come to treat of them individually. We may now observe, that, how varied soever they may appear, when viewed only in their extreme results, yet all these variations seem to spring from a few original differences in character; which differences, modified by circumstances of subsequent duration and growth, produce, by gradations almost insensible, the manifold diversities of form and structure, which hereafter we shall attempt to describe.

132. In our discussion of those several textures, we have noticed only in a general way, the direct means by which the vessels and cells that construct them are connected with each other; but, when treating of the sap-vessels of the absorbent vessels, and of the cellular tissue, we endeavoured to show, that an universal communication obtains between these elementary organs, and consequently inferred, that some mode of connection, by which it can be accomplished, must have place. Grew considered Opinion of the vascular and cellular parts to be connected with each other, not only by the transverse partitions of cellular substance that intercept the vessels—but "per minimas partes organicas;" that is to say, the parenchymous fibres are wrapped round about the vessels, or at least interwoven with them, and with every fibre of every vessel, as in very white ash or fir wood may be observed." (Anat. of Plants, p. 121.) These fibres, Grew elsewhere considers as vessels, and consequently must be regarded as maintaining, with Malpighi, a vascular connection between these organs. In a description of the young branches of of Mal- Chesnut and Oak, Malpighi delineates minute filaments, springing on every side from the vessels of the wood, and continued into the adjacent cellular tissue (Anat. Plantar. p. 27.), but he does not state whether they are to be regarded as vessels or simple fibres. We have before shown, however, that he considered the cells to be everywhere furnished with minute ramifications derived from the perpendicular vessels; and, indeed, he held it probable, that the nutrient fluids, moving through the vessels, were, in all parts, poured into the cells, and there undergoing a certain preparation, were afterwards mixed with more recent juices, and with them taken up and applied to the support of the young buds and leaves. (Anat. Plantar. p. 30.) This doctrine has since been held by Darwin and Knight, and it necessarily supposes a vascular connection between the vessels and the cells, by which the functions both of secretion and absorption can be performed. The microscopical observations of Leuwenhoeck, already noticed, supply farther evidence in support of this opinion.

133. In the hypothesis of Mirbel, both cells and vessels are considered as one and the same membrane. He rejects, therefore, the aid of all intermediate organs, as necessary to connect them together; and supposes a communication to be everywhere maintained between the vessels and cells, by the medium of pores in their sides. As, however, these pores are nowhere proved to have existence but in the imagination of the author, we may altogether reject their agency in maintaining a communication betwixt the vessels and cells of plants. In the opinion of M. Kieser, the conjunction of the cells with the vessels is extremely simple, the sides of the cells, says he, being contiguous to the sides of the vessels.

(Mém. sur l'Organisation des Plantes, p. 94.) But mere contiguity of parts does not amount to connection, much less does it afford any information concerning the actual communication that exists between these organs. In addition, therefore, to connection by cellular substance, it seems absolutely necessary to suppose also the existence of a vascular structure, which shall at once serve as a medium both of connection and communication.

134. Before concluding this branch of the subject, we may observe that the structure of the cellular tissue, and its relation to the vascular system in plants, appears, in many points, to resemble that of the adipose cells, and their relation to the vascular system of animals. These cells are described as minute close cavities, possessing no apparent communication with each other; and within them adipose matter is alternately deposited and removed. Now, the deposition of this matter could only be accomplished by secreting vessels, which terminated in the cells, and its removal be effected by absorbents, which originated from them; and accordingly, both blood-vessels and absorbents are found to be present in this texture; but neither the secreting nor absorbing orifices have ever been actually observed. Within the cells of the cellular tissue of plants, the alternate deposition and removal of various matters are not less certain; and in the germinating seed, the matter that actually existed in the cells is found afterwards in the vessels. We are led, therefore, or rather we are driven, not only by the direct exclusion of all other alleged means of communication, but by a close analogy in the exercise of these animal and vegetable functions, to conclude, that secreting and absorbing vessels must be employed to deposit and remove the secreted matter from the cells of plants, in the same way as they are considered to effect similar depositions and removals of adipose matter from the cells of animals; and as this alternate function seems to go on in every part of the plant, capable of active vegetation, it may farther be inferred, that a vascular connection and communication exists between the vessels and cells in all parts of the vegetable system.

135. By means of this general communication between the vessels and the cells, we are enabled to assign satisfactory reasons for some puzzling phenomena, which have occurred in relation to the movements of the sap. It is by this alternate action of secretion and absorption, that, in young plants, we must suppose the cells of the pith, during the first year, to be filled with fluid; and to be rendered dry for the most part ever after. In like manner, the surface of the bark, in contact with the wood, appears, in some trees, as the Birch, to be rendered moist during the rise of the sap in spring; which led Dr Wal-

ker and others to suppose, that the sap rose in part betwixt the bark and the wood; an opinion not at all probable in itself, and certainly not supported by what is observed in most other trees. The fact, however, is easily explicable, on the supposition that the sap was transposed from the albuminous vessels of the wood, in the same manner as, at a later period, it is secreted in the same part, but in a different form, by the vessels of the bark, to form the new matter that is annually added to the tree.

136. That the sap of plants was capable of moving in a lateral direction, was inferred by Malpighi from the fact that parts lived and grew, when the perpendicular vessels that supplied them with nutriment had been destroyed. (Anat. Plantar, p. 13.) The experiments of Hales afford more decisive evidence regarding this lateral movement of the sap. He cut two large gaps in the opposite sides of an Oak branch, at four inches distance from each other, carrying the incisions down to the pith; the branch nevertheless absorbed and perspired water, but only in half the quantity that another similar, but uncut, branch did. In branch of Cherry-tree, he made four similar cuts down to the pith, at four inches distance from each other, and opposed to the four points of the compass; the branch notwithstanding absorbed, in forty-eight hours, twenty-four ounces of water. (Veg. Statics, p. 128, 3d Edit.) And when similar incisions were made on branches, while still attached to the tree, their leaves continued green, nearly as long as those of other branches in a natural state; whence he justly inferred, that, at these gaps made in the branch, a lateral movement of the sap must have taken place. Experiments of a similar nature have been made, and like results obtained, by Mr Knight (Phil. Trans. 1808); so that it seems clear, that, in certain circumstances, a lateral movement of the sap must have place.

137. In what manner, then, must we suppose this movement to be accomplished? Grew supposed the cellular tissue, that stretches from the circumference to the centre of the plant, to be the instrument by which such a communication could be maintained; but the impermeability of this tissue to fluids opposes such an opinion. Malpighi thought the lateral communication to be made by an anastomosis of vessels; but in the vessels of plants no such mode of communication appears to exist. From the ascent of the sap in branches in which the vessels had been thus previously cut through, Mr Knight infers, that this fluid does not rise in the vessels at all, but is conveyed through the cellular tissue. This opinion necessarily implies the permeability of this tissue by fluids, which, as we have shown, is contradicted by direct experiment, as well as by microscopical observation. Since, therefore, this lateral movement of the sap cannot be accomplished, either by simple percolation through the cells or vessels, or by direct anastomosis of the vessels with one another, no other known means of effecting it remain, but those of alternate deposition and absorption by the vessels into and from the cells. And if, as we have seen, the sap-vessels of plants deposit coloured fluids in the cells which the capillary absorbents of parasitic plants are able to take up, there seems no reason for deny- ing to the vascular productions, which have been supposed everywhere to spring from the perpendicular vessels, a like capacity of absorbing fluids from the adjacent cells. These fluids must, however, in all cases, have been deposited before they could be absorbed; and by the alternate exercise of these functions, there is no difficulty in conceiving how a lateral movement of the sap might be accomplished, in parts, where, by the incision of the vessels, a stop was necessarily put to its perpendicular ascent.

Section IV. Of the Skin or Cuticular Texture, and its Appendages.

Article I. Description and Structure of the Skin.

138. The skin, rind, cuticle, or epidermis, as it has been variously named, is the last of the common textures that remains to be described. It is the general envelope which invests all parts of the plant and all its productions, being equally common to the trunk and branches, the root, the leaves, the flowers, and the fruit; but in these different parts, and even in similar parts of different plants, it exhibits the greatest diversity of appearance, form, and texture.

139. In herbaceous plants, and in the young shoots of those which are arborescent, it resembles a thin membrane, but is generally thicker on the stem than on the roots or leaves, and is of still more delicate texture where it is extended on the flowers. In some leaves, however, it is thick and dense, as is the case also in several fruits, and is thereby fitted to resist the effects of too rapid desiccation. On the upper surface of some leaves, on many fruits, and on roots, it is an entire membrane, destitute of any apertures or pores; but on many stems, on the under surfaces of leaves, and sometimes on the upper, it is frequently furnished with numerous pores, often visible to the naked eye, and with other luminous points of smaller dimensions, which Du Hamel also regards as apertures. It is readily separable from the bark in recent and succulent parts, or after maceration in water; and, in certain leaves, it is very completely separated by a species of caterpillar, named by Reaumur, the miner. It appears then to be a thin transparent membrane, often destitute of colour, and deriving, therefore, its appearance from the colour of the parts beneath; but both in leaves and flowers it is often itself coloured. It is frequently seen to extend in all its dimensions, in common with the parts it covers. Very often too, as will be noticed hereafter, its surface is covered with hairs, and sometimes small follicles or utricles are met with, which exercise a glandular function.

140. The characters above enumerated belong chiefly to the cuticle in its young and succulent state; in perennial plants, it commonly possesses others that are quite dissimilar. It is of a different colour not only on different trees, but on different parts of the same tree. It is white and shining on the trunk of the Birch, and browner on the branches; greyish on the Plum-tree; red and silvery on the Cherry; green on the young branches of the Peach, and ash-coloured on the larger branches.

In these and many other instances, it does not, says Du Hamel, merely participate in the colour of the body it covers, but contributes itself to give colour to the exterior bark; for when it is stripped off, the substance below has frequently a different colour. (Phys. des Arbres, Tom. I. p. 10.) By the gradual enlargement of the trunk it is stretched and dried, and at length loses its vitality, and, as well as the bark beneath, is variously cracked and broken. Before this happens, however, it often undergoes considerable extension in all its dimensions, enlarging in breadth, and stretching longitudinally over the young shoots. This expanded state is particularly remarkable in certain fruits, in which, when they enlarge slowly, the cuticle is extended without rupture, to a very large size; but if the expansion be very rapid, as after considerable rains, the cuticle then gives way. In certain trees, the cuticle is more susceptible of expansion than in others; and in very vigorous trees, it breaks more slowly than in those whose growth is languishing; although these latter push forward more slowly than the former. (Ibid. p. 11.) In some vigorous trees of this description, it altogether resists rupture, and in this state the tree is often said to be hide-bound, or bark-bound.

141. In most instances, the cuticle, when taken Composed from young branches, appears to consist of a single layer; but on the branches of many species, says Du Hamel, after one plate or layer has been removed, another may be seen beneath, which resembles the former in its texture, but is much thinner and more green and succulent. From the Birch-tree, he has removed more than six layers; very thin and very distinct from each other, and is of opinion that more might still be separated. Sometimes the original cuticle seems to be entirely thrown off, and the exterior covering is formed by a portion of the cellular tissue of the bark. Grew thinks that this substitution takes place annually, the older skin being cast off like the skin of an adder, by the generation of a new one beneath. (Anat. of Plants, p. 114.) Du Hamel describes also the existence of small leaflets or scales, which are continually detached from the cuticle of some trees; and these he considers to be as constantly replaced, by the formation of new ones beneath them.

142. Concerning the regeneration of the cuticle, Du Hamel observes, that when the wound is covered with waxed-cloth, a new cuticle is promptly formed without any separation of a portion of the bark beneath. When the exterior portion of the bark is removed with the skin, the inner part of it is equally capable of regenerating a cuticle; but if the wound be not protected from the air, a certain degree of exfoliation first occurs, and, under the decayed parts, a new skin forms. Even where the bark of a Cherry-tree was entirely removed from the trunk, he found that the wood was capable of regenerating a new bark and cuticle, if the parts were properly protected from the air. This cuticle did not originate from that which remained on the roots and branches; but was reproduced in isolated portions on different parts of the trunk; it continued, however, after the

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Common lapse of fifteen years, always different from that of the natural growth. In other instances, he adds, the cuticle does not seem to be regenerated at all. He remarks certain analogies to exist between the cuticle in some plants and animals. Both, he adds, seem, in certain circumstances, capable of great extension; both are easily regenerated, and that in isolated portions, and not by continuity of organs, as is common in other instances; and both, lastly, are perpetually obliterated, and continually and imperceptibly renewed. (Phys. des Arbres, Tom. I. p. 11.)

Its Nature.

143. With respect to the nature of the cuticle, very different opinions have been advanced, and still continue to prevail. Are we to regard it as a peculiar organ, formed immediately by the proper exercise of the vegetative functions, or is it produced in a sort of secondary manner, by some changes induced on some previously constructed organ? Grew asserted it to be sometimes original, and in some instances produced out of the exterior layer of the cortical texture beneath it; and this view of its origin seems to be generally supported by the descriptive character which has been assigned to it. Its coexistence with the first traces of vegetable organization, its continued growth and expansion, and its subsequent regeneration, after removal, all seem to favour its primary and independent origin; and this view is also supported by investigations into its minute structure. Mirbel, however, and some other writers after Hill, have regarded it, in all cases, not as an original membrane, but formed by the exterior sides of the common tissue of the plant; and where there is no separation of these sides in the form of a membrane, such plants are held to be destitute of a cuticle. (Exposit. de l'Organisat. Veg. p. 103.) This may assimilate very well with the mechanical views that pervade all this author's speculations concerning vegetable organization; but will, we suspect, make few converts among those accustomed to contemplate the powers and properties of living textures.

144. Another question relating to this organ is, Whether it must be considered a simple membrane of uniform structure, or a compound of two distinct parts, like the true skin and the cuticle in animals? Grew seems to have regarded it as a simple body, but constructed both of vessels and cells, the cells being continuous with those of the bark. (Anat. of Plants, p. 62.) Such too seems to have been nearly the opinion of Malpighi, who describes it as constructed of horizontal ranges of cells, but often delineates reticulations of vessels as constituting a part of its structure. (Anat. Plantar. p. 2—19.) In the Birch, the Plum, the Cherry-tree, and others, Du Hamel declares the component fibres of the cuticle to possess a direction transverse to that of the trunk; but this is not general. In the Birch-tree, the fibres seemed to be placed parallel to each other, and to be connected together by lateral fibres; but he could see nothing of the vesicular structure of Malpighi and Grew, and regards, therefore, the structure of this texture to be altogether fibrous. (Phys. des Arbres, Tom. I. p. 8 and 9.) M. Desfontaines, on the other hand, describes it as a membrane, resembling in appearance a thin plate of parchment, and perforated by imperceptible pores, which give issue to the insensible transpiration. Its structure he regards as unknown, but considers it capable of regeneration. (Mém. de l'Inst. Nat. Tom. I. p. 481.)

145. M. Kieser, who professes to have studied this texture with great attention, adopts nearly the opinion of Grew; pronouncing the cuticle to be constructed of a very fine cellular tissue, and of extremely minute vessels, which run through its whole extent. These vessels form an exceedingly delicate and subtle net-work, the meshes of which possess very different forms, and their vessels terminate at the orifice of a pore. His observations were made on the cuticle of leaves. On the inferior surface of the leaf of Amaryllis formosissima, (fig. 14. A. Plate XVIII.) magnified 260 times, these vascular meshes of the cuticle have an elongated hexagonal form; and four of their vessels proceed always to terminate at the orifice of the little oblong aperture or pore situated at their junction. In Canna Indica, the vessels of the meshes on the lower part of the leaf, which thus terminate in the pores, are said to originate from a fasciculus of the spiral vessels that ramify through the leaf; as is represented at a' in fig. 14. B. Plate XVIII.; and within the areas of the larger meshes, a still finer net-work of vessels is seen. On the inferior surface of the leaf of a species of Fern, the vessels of the cuticle, instead of forming meshes of different figures, exhibit the appearance of sinuous lines, which run in every direction through the cuticle. See fig. 15. Plate XVIII., which represents the central part of the little adjoining leaf, magnified 180 times. These sinuous vessels often join, and, after making a half circle, terminate by one extremity in the minute pores everywhere spread over the leaf, and by the other in the larger vascular fasciculi that ramify through it. At the letter b', in this figure, the hexagonal cells that construct the parenchyme of the leaf, are distinctly visible through the vascular sinuosities of the cuticle. It was by the examination of this leaf that M. Kieser was first enabled to discover the origin and termination of the vessels that construct the cuticle; having in all his previous investigations examined the cuticle in its separated state, after it was detached from its connection with the other organs; but the researches made on this leaf rendered everything clear. (Mém. sur l'Organisat. des Plantes, p. 141-2.)

146. The vascular net-work of the cuticle, thus described by M. Kieser and others, had been regarded as a deception by M. Krocker, who considered these reticulated figures as no part of the real structure of the cuticle, but merely as the sides of the subjacent cells; in which opinion, Sprengel, Link, Jurine, and Mirbel, concurred; but M. Kieser, in opposition to this opinion, maintains that, in the Fern and other leaves, the real cellular structure of the parenchyme is seen entire through the vascular reticulations of the cuticle, with the meshes of which the sides of the subjacent cells do not anywhere coincide. He observes that these cells are commonly much smaller than the vascular meshes which cover them; and that the vessels of these meshes may be traced, as before remarked, to the larger fasciculi that construct the leaf. In the Fern, the vascular structure of the cuti-

VEGETABLE.

147. A very different view of the structure of the cuticle was taken by the late celebrated M. De Saussure. He regarded it not as a simple, but a compound texture, consisting of a very delicate external pellicle or membrane, beneath which was placed a net-work of very fine vessels. The external membrane he describes as perforated by pores of unequal figure, between which he observed some opaque and tortuous filaments, disposed in a reticulated manner, each mesh being formed by six filaments, four of which terminated at each pore. To this arrangement of filaments, he gave the name of cortical network, and regarded it as quite distinct from the cuticle that covered it. The meshes of this net-work differ much in size and figure in different leaves; and, when minutely examined, they are often seen to form junctions, but never to cross each other; whence he was led to regard them as vessels derived from those of the expanded petiole, and thus constituting a very fine vascular net-work. A similar structure was observed in the petals of the flower. (Encyclop. Méthod. Tom. I. p. 67.)

148. M. Decandolle, to whose researches we before alluded when treating of the absorbent system, adopts a similar view of the compound nature of this texture. He describes it as consisting of a proper cuticle, and of a cortical net-work, the vessels of which terminate at oval pores, more or less elongated. Around these pores, the vessels (or fibres, as he calls them) form an oval ring, which is connected to the rest of the net-work, by two, three, or four radiating vessels, derived from the vessels of the petiole. These vessels of the petiole he considers to form, first, the larger vascular fasciculi; then, by their subdivision, the parenchymic of the leaf, and afterwards to construct the net-work that terminates at the pores. The form of the meshes of the vascular rings, and of the pores, is the same always in the same species, and on the same faces of the stem, the leaves, and the flowers. (Mém. de l'Institut Nat. Tom. I. p. 351.)

149. Such are the very different opinions held by enlightened observers concerning this texture. Each professes to have given descriptions from accurate microscopical observation, and it would therefore be presumptuous, on mere reasoning alone, to decide on their respective merits. Granting to each party similar credit, as far as regards accuracy of observation, we confess that the latter opinion seems to us, on other grounds, best entitled to preference. In both views, the direct connection of the vascular system with the external pores of the leaf is admitted, which is perhaps the most important point in the inquiry; and the only difference is, whether these vessels shall be regarded as a constituent part of the cuticle itself, or as forming a fine vascular net-work, connected with, but still distinct from it.

ARTICLE II.

Of the Pores of the Skin.

150. The pores of the cuticle, called sometimes cortical or miliary glands, so often mentioned already, deserve a more detailed description. They were first noticed by Grew, who describes many orifices as existing on the leaves of different plants, which vary in size, number, shape, and position. In the white lily, they are of an oval shape, of a white colour, and each is surrounded by a slender border. When viewed through a good glass, they appear as if standing about \( \frac{1}{4} \) th or \( \frac{1}{2} \) th of an inch apart all over the leaf, but not arranged in any regular order. In the Pine also, they have an oval shape, but have no rising border; and are arranged in lines from one end of the leaf to the other. (Anat. of Plants, p. 153.) Hedwig considered the borders mentioned by Grew, as produced by a ring of one or more vessels which terminated in the pore. The number of pores he represents as exceedingly great. In the square of a line of the cuticle of a bulbous lily, he reckoned 577 pores.

151. The characters and position of these pores by Decandolle have been farther examined by M. Decandolle, on more than 600 plants. They occur most frequently on the leaves, occupying both surfaces in herbs, and in trees chiefly the inferior surface. Stems, in general, have no pores, except, as in the Gramineae, where they are succulent, and have the character of leaves, or where the plant is altogether destitute of leaves, as the Cactus. On the prominent lines of the leaves and stems, no pores are to be seen, but only in the grooves or depressed surfaces. They are never observed on the root, not even on bulbous roots, where the scales of the bulb are true leaves. The small leaflets called stipule and bractæ, sometimes have, and sometimes have not, pores. The calices of the flower, in general, have pores, but the petals have not. Pericarps exhibit great variety in regard to pores; fleshy fruits are generally destitute of them. The envelopes of the seed are destitute of pores, but they are found on all seminal leaves that rise above the ground. The lower tribes of vegetables, as the fuci, musci, hepaticæ, fungæ, &c., are destitute of pores.

152. The occurrence of pores in those plants where they are found, seems to be much influenced by external circumstances. They are never met with but on vegetables, and those parts of vegetables that are exposed to the air; and, therefore, the internal surfaces of many leaves that embrace the stem are without pores, though, on the external surfaces of the same leaves, they are abundant. No plant that is completely aquatic, nor any part of it that is habitually under water, is provided with these organs, but the parts which rise above the water, are furnished with them. In Ranunculus aquatilis, the leaves that are constantly under water, are destitute of pores, while those that float on the surface are provided with them, but only on their superior face. Even leaves, which do not naturally possess pores when under water, acquire them if they are made to grow in air; and land plants, on the contrary, when made to grow under water, may, by such treatment, be deprived of their pores. Thus, the leaf of green mint, when growing in air, possesses not fewer than 1800 pores on its lower surface; but if kept for a month under water, its leaves fall, and the new ones that succeed are destitute of pores. 153. Light seems to be necessary also to the production of pores, for etiolated plants do not possess them. When grown by the light of lamps, the leaves possess a few pores; and in all cases, the parts secluded from light and air are destitute of these organs, but acquire them if they are duly exposed. These pores, M. Decandolle, as we had before occasion to remark, considers to perform alternately the functions both of transpiration and absorption. (Mém. de l'Instit. Nat. Tom. I. p. 351.)

154. This general account of the pores of plants is confirmed by the researches of M. Rudolph. In most herbaceous plants, he found the pores to occupy both sides of the leaf, but in trees, only the inferior surface. They were not often met with on the parts of the flowers, or on fruits; they were never seen on roots, nor on the trunks of trees; nor ever on aquatic plants, except on such parts as were raised above the water. The lower tribes of vegetables seemed to be universally destitute of them; the leaves also of those plants that were covered thickly with hairs on both sides had no pores. The form of the pores was commonly oval or elliptical, but in a few instances square or rhomboidal. In size they very much varied in different plants, but in the same plant the size was uniform. The largest pores were seen on the leaf of the white lily; the smallest on that of the French bean. (Kieser's Mém. sur l'Organisation des Plantes, p. 144.)

155. From these accounts of the occurrence of pores, and of the conditions necessary to their production, they cannot be considered as an essential, or indeed a primary character of the cuticle; but as owing their existence to the more perfect exercise of the vegetable powers. Hence the probability that they are caused by innumerable vascular productions from the larger fasciculi of vessels, which gradually penetrate the cuticle, and thus open a way for the discharge of their fluids, as the researches of De Saussure and Kieser seem to prove. That the exclusion of air and light should prevent the formation of pores in the cuticle, is nothing more than we see daily on a larger scale, with regard to branches themselves; for trees that grow very much crowded together, seldom produce branches from their sides; and if herbaceous plants be made to grow entirely secluded from light, they run altogether into stalk, and produce no buds or leaves from their sides.

Article III.

Of Hairs.

156. From the surface of the cuticle, in many parts of herbaceous plants, and in the succulent parts of arborescent ones, hairs (pili) are seen to spring. They possess very different forms, and vary likewise greatly in texture. In a strict sense, they may be defined small filaments possessing considerable stiffness, which project from the surface, and stand out pretty erect. When they are very numerous, a little soft, and less erect, they take the name of villi; when still softer and less numerous, they are termed down (pubes). Sometimes this down is composed of long hairs nearly resembling wool; at other times it approaches more to the character of cotton. When the hairs are stiff and ranged along the edge of a surface, like the lashes of the eye, they are named cilia; and if, with these characters, they are produced to a greater length, as in the beard or awn of wheat, they acquire the name of barba or arista. Sometimes they resemble the bristles of the hog, and are then called setae. Many other varieties are enumerated by botanists, who farther distinguish them by various names, according as they terminate in a single point, or are hooked, or forked, or branched, or feathered, &c. In some instances, instead of appearing like one continuous substance, they are composed of many joints, or are said to be articulated. In figures 16 and 17, Plate XVIII., we have copied from Du Hamel a few of the varieties, both of single and jointed hairs; but the forms they exhibit are so numerous and diversified, that we must refer to the writers on botany for minuter information. In some examples, the point of the hair is terminated by a small rounded globule, and sometimes by a fine filament that seems to proceed out of the hair.

157. According to M. Decandolle, these several varieties of hairs appear generally on those parts of the stem and leaves that are destitute of pores; that is, on the prominent lines formed by the fasciculi of vessels, and which have been absurdly called the nerves of the leaves. They appear also on the edges of leaves, whose pores are never seen, so that, in position, the hairs and pores always differ. (Mém. de l'Institut. Nat. Tom. I.) On the petals of flowers, as well as on leaves, various capillary productions also occur, which frequently contribute much to their richness and beauty.

158. With regard to the structure of these minute bodies, little that is satisfactory can be said. They seem to originate either directly from the cuticle, or from the cortical texture beneath it; but not often from the ligneous texture, except in those instances where they are very long and rigid, as in the awns of wheat. Du Hamel observes, that almost all of them are implanted on small bodies, similar to the bulbs which give origin to the hairs of animals, (Phys. des Arbres, Tom. I. p. 183.) They commonly resemble simple filaments, but often appear like elongated cells threaded on one another, and, instead of terminating in a sharp point, end in a small papilla or utricle, which yields, in many instances, a viscid or oily matter, or sometimes a coloured liquor, which has led many to regard them as exercising a glandular function. One species of these supposed glandular organs has been more particularly studied, and their fluid analysed by M. Deyeux, who gives the following account of it.

159. Soon after the seeds of the chick-pea (Cicer arietinum) are sown, its first leaves are seen to be covered with hairs, at the extremity of each of which is a transparent globule, about the size of a small pin head, consisting of a fluid matter. It abounds most in mid-day, when the air is warm and dry, and is scarcely perceptible at night, or when the air is cold and moist; after rain, indeed, it does not again appear for two or three days. When these fluid globules were removed, in a dry day, by blotting paper, they soon again reappeared; they were acid to the taste, reddened litmus paper, and caused an effervescence in carbonate of potass, when brought in contact with it. He regarded them as composed of oxalic acid, the properties of which they precisely resembled. (Mém. de l'Instit. Nat. Tom. I. p. 157.)

160. These acid globules, and perhaps the other viscid, and oleaginous, or resinous substances furnished by hairs, are not, properly speaking, glandular secretions; but cellular fluids, which, after their separation from the fluids of the leaf, experience certain changes from the agency of heat and light, during their passage through these delicate organs. There does not, therefore, seem any good reason for considering such bodies as glands. Many have considered these hairs, as the organs by which transpiration is carried on, and others, as those by which dews and fluids are absorbed—offices for which their structure seems but little fitted; and the transpiring and absorbing powers of leaves, are in proportion to the number of their pores, and not of their hairs. In many instances, they are obviously designed for protection against cold and moisture; but this is not the place to consider their uses, farther than is necessary to assist in establishing their anatomical character.

Article IV.

Of Prickles.

161. It is not easy to discriminate between some of the harder species of hairs, described in the former article, and those to which the appellation of prickles (aculei) has been assigned. They are defined by Du Hamel to be excrescences, often hard, and always terminated by a sharp point, which are developed with the other productions of plants, but are not enclosed in particular buds; so that they may, for the most part, be regarded as hard and solid hairs.

162. They spring equally from the stem, the branches, the petioles of the leaves, and also from the leaves themselves in various plants; and in the Chestnut and some others, they are seen to cover the fruit. They are frequently straight, but in the Rose and many others are curved at the point, as in fig. 18. Plate XVIII.; and, according to Malpighi, possess sometimes in this plant a little head, which yields a viscid fluid.

163. Regarding their structure, Grew remarked, that they were connected only with the skin or the bark, and he therefore named them cortical, to distinguish them from thorns, properly so called, such as those of the Hawthorn, which spring from the wood, and which he denominates ligneous. These latter, he adds, always ascend, while the cortical thorns commonly point downwards. (Anat. of Plants, p. 33.) In proof of their origin from the bark, Du Hamel remarks, that, if, after maceration in boiling water, the bark of such plants be stripped off, all the prickles come away with it, and leave not the smallest impression on the wood, nor even on the more interior layers of the bark itself. When a section also is made of the branch and prickle, as in fig. 18. Plate XVIII. the wood y and the pith z are both seen to have no connection with the prickle, but the inner layer of the bark x is interposed between the base of the prickle and the wood. The prickle does not, however, spring from the skin, for it is formed of many layers like the bark. As the parts become more solid, it is less freely supplied with juice, and therefore hardens and turns brown. (Phys. des Arbres, Tom. I. p. 188.)

164. In the Nettle (Urtica dioica), Malpighi prickle of states, that, beside the common prickles on the leaves, the Nettle, there are among them others of a different description. They possess more of a ligneous character, are hollow internally, and contain a juice, which, when it gains admission beneath the skin, excites itching and tumour. (Anat. Plantar. p. 137.) Dr Hooke had previously given a much more minute account of the sting of this plant. Almost every part of it, says he, is covered with prickles, like sharp needles. Each prickle consists of two parts, very different in shape and quality from one another; one is shaped much like a round bodkin, is very hard and stiff, exceedingly transparent and clear, and hollow from top to bottom. When this bodkin is thrust into the skin, it does not at all bend; but a certain liquor is then seen to move up and down in it, rising towards the top, when the point is pressed down on the base. This base is formed by a little bag, is more pliable than the bodkin part, and within it is a cellular structure which contains a thin transparent liquor; see fig. 19. Plate XVIII.; it is this liquor that rises in the tube, and, being deposited beneath the skin after it is punctured, excites the irritation that succeeds. (Micrographia, p. 142.)

From the analogy in structure between thorns, properly so called, and branches, we shall defer their consideration until we come to treat of the structure of the branch.

Section V.

Of the Glands of Vegetables.

165. Perhaps, in the whole science of Anatomy, there is no word that has been employed with such latitude of signification, and is, therefore, exposed to so much ambiguity, as the term gland. In animal anatomy it was doubtless used at first to denominate certain organs from the external resemblance which they bore to certain fruits or seeds; and in that sense it is still employed on several occasions. Afterwards, it was understood to signify not so much the external form as the internal organization, and was considered to express a certain structure, by which alone the function of secretion could be exercised; but it is well observed by Dr Thomson, in his valuable work on Inflammation, that "the definition of a secreting glandular part must be taken from its function, and not from its structure; for nothing can be more various than the internal structure of those organs that are denominated glandular secreting organs; they consist sometimes of convoluted vessels, sometimes of follicles or small hollow bags, and sometimes of transparent membranes, in which neither convoluted vessels, nor mucous follicles, can be perceived." (Lectures on Inflammation, p. 318.) Besides these more simple structures, it is well known that most of the internal viscera are likewise denominated glands, though differing, in all their characters, from those just mentioned. 166. The ambiguity which thus prevails in animal anatomy, in relation to the use of the term gland, has been increased tenfold in the applications that have been made of it to the organs of vegetables. It is justly observed by M. Decandolle, in reference to this subject, that the numerous approximations in structure between vegetables and animals have often promoted our researches into the former, but have sometimes led physiologists astray, and introduced into the language of botany many inexact expressions. In animal anatomy, the term gland is understood to express some organ that exercises a secretory function; but, in vegetable anatomy, this term has often been applied to bodies that are not known to be real secretory organs. Thus, the cells of the cellular tissue, which frequently contain resinous or oily matter, have been sometimes named cellular glands; the little globules or utricles at the extremities of the hairs on the edges of leaves, utricular glands; the small organs formed by the pores on the leaf, cortical or milky glands; certain fleshy tubercles on the leaves, urceolar glands; and the little scales that cover the fructification in ferns, scalyform glands. The nectarium of the flower commonly contains a sweet juice, and is, therefore, deemed a gland; but Linnaeus, with his usual disregard both of the structure and function of organs, considers as a nectary, not only the body which may secrete, but any other that may serve as a receptacle of the secretion; and, indeed, is said to comprehend under this term all those bodies which have no resemblance to the other parts of the flower, in whatever variety of form they may appear, or whatever purpose they may serve. (Willdenow's Prin. of Botany, p. 87.) In some other instances, the term gland has been used not to express the secreting organ itself, nor even the receptacle of the secretion, but the solid excreted matter on the surface of certain leaves; and others consider hairs, and every other protuberance that projects from the surface, and contains a fluid different from the common sap, as entitled to the distinctive appellation of gland.

167. Amid such diversity of opinion concerning the structure, position, and function of these minute organs, and such vagueness in the methods employed to characterize them, it is extremely difficult to define their true nature, or declare the principle on which this definition should proceed. The mere existence of a fluid, distinct from the common sap in any organ, cannot be considered as bestowing on it the title of gland, otherwise the greater portion of some plants would come to be regarded as glandular; those varieties of structure, which exercise no secretory function, may also be excluded from the list of glands; and so likewise the hairs of plants, though containing peculiar fluids, may be excluded, since these peculiarities appear to arise frequently from circumstances foreign to the action of the organ itself; and even if they do not, some specific variation of the general name they bear is preferable to the employment of so ambiguous a word as gland. But where any organ is distinct from the common textures of the vegetable, and, by the peculiarity of its structure, is fitted to produce those changes on the vegetable fluids which we name secretion, it may be deemed a secreting organ. This secretory function, however, may sometimes be exercised, as in animal bodies, by membranous surfaces, and sometimes by small isolated bodies, to which, perhaps, may properly belong the denomination of glands.

168. But, even though this method of defining glands were adopted, it still is a matter of no small difficulty to distinguish their species by appropriate appellations. In animal anatomy, no settled rule obtains; but the name of the gland is assigned from some accidental circumstance of situation, figure, use, &c. In vegetable anatomy, the botanist, regarding glands only as aiding the discrimination of species, refers commonly to their situation, and speaks of foliaceous, stipular, or petiolar glands, according as they happen to be seated on the leaves, the stipule, or the petioles. The anatomist imposes names according to their forms, as they chance most to resemble a globule, an utricle, or some other figure; and the physiologist is chiefly directed by ideas which indicate their functions, distinguishing them into mucous, oily, resinous, or nectariferous glands, according to the nature of the fluid they furnish. Of these different modes, that which proceeds on the apparent form, where it can be discovered, seems the most precise; but as this cannot always be accomplished, the situation of the organ, or the nature of the secreted fluid, must occasionally be had recourse to.

169. Of these bodies, it is to be remarked that they differ in one respect from most of the corresponding organs in animals, almost all of them being seated on the external parts of the plant, like several of the more simple glandular bodies in animals. This arises from the greater simplicity of vegetable organization, particularly as it regards the absorbent system, the mode of growth, and the permanence of the organs produced; whence it happens that the living parts of aged perennial plants are situated only at, or near the surface; and it is only in such parts that active secretory functions can have place. Hence it is on succulent stems, on leaves, flowers, and fruits, during the active state of vegetation, that the glandular functions of vegetables must be exercised, and which parts, therefore, are the appropriate seat of glands.

170. In some leaves a secretory function extends over a great part of the surface, as in some species of Cistus, of Sugar-maple, of Larch, and others, enumerated by Du Hamel, on which various collections of saccharine, gummy, and resinous matter are found. (Phys. des Arbres, Tom. I. p. 183.) On the leaves of Sage, Hooke mentions the occurrence of an infinite number of round balls resembling pearls, and which, says he, are nothing but a gummy exudation. (Micrographia, p. 142.) M. Guettard has described by Gastonier fewer than seven species of glandular bodies on the leaves of different plants, to which he assigned names, chiefly from the appearance of their form; these are the milky, the vesicular, the squamous, the globular, the lenticular, the utricular, and the urceolar glands. Of these reputed species, those called milky are no longer held to be glands, but cuticular pores; and the squamous species is found to be identical with the thin scale that covers the fructification of ferns. Others add to this list the organ called nectary; but the very vague notions entertained of its nature and use altogether preclude the possibility of assigning to it any precise anatomical character.

171. Other writers have proposed to reduce all the bodies called glands to two classes, the cellular and the vascular, according as they conceive them to be formed of cellular tissue simply, or of this tissue and vessels combined. But such an arrangement would lead us, in some instances, to confound the mere receptacles of secreted fluids with the organs that secrete them; would bestow a secretory function on organs, considered by these writers to be non-vascular; and convert the entire cellular tissue of the plant into a simple glandular body. The glands of plants may indeed possess the form and size of cells; but they are not, like cells, close cavities; they resemble more the follicles and mucous glands of the animal system, and, from the nature of their function, must always be regarded as vascular.

Of organs so minute, and so very imperfectly known and characterized, nothing can be attempted in the way of anatomical demonstration. This, however, is the less to be regretted, as the glandular system in plants appears, in general, to be of much less consequence in the vegetable, than it is in the animal economy.

PART II.

THE ANATOMY OF THE INDIVIDUAL MEMBERS AND ORGANS OF VEGETABLES.

172. In the preceding Part, we have described, in general, the nature of the elementary organs and common textures that compose the entire plant; and we come now to the second division of our subject; viz. the description of individual members and organs. Following the method of Grew, we shall first exhibit the anatomy of the seed, and the changes of form and structure displayed in its evolution. We shall next treat of the mature plant, and exhibit views of the more remarkable varieties of structure observed in its several members, as the trunk, the branch, and the root. The organs that originate from these members, as buds, leaves, flowers, and fruits, will then be duly noticed; and we shall terminate our descriptions by a brief exhibition of the formation and structure of the vegetable ovum in its progress towards the state of the perfect seed.

The limits within which, in a work like the present, we are necessarily circumscribed, will render our view of these individual structures, when compared with the immense variety that obtains in nature, exceedingly imperfect; but our purpose will be accomplished, if we succeed in exhibiting a correct and tolerably comprehensive outline of the great features of vegetable organization, as they are displayed in the individual parts and organs of the more perfect plants.

CHAP. I.

THE ANATOMY OF SEEDS.

SECTION I.

Of the Structure of Seeds in general.

ARTICLE I.

Of the External Characters and Component Parts of Seeds.

173. The seed or egg of vegetables (semen vel ovum) is formed at the base of the pistil of the flower, in an organ called the ovary (ovarium), its attachment hereafter to be described. To this organ it is attached by a small stalk, called the umbilical cord (funiculus umbilicalis); but sometimes, it is said, this cord, probably from its extreme tenuity, or implication with other organs, cannot be discovered. When the seed has attained to maturity, the umbilical cord dries up and breaks; and the ovary, in different plants, opens in various ways, to permit the escape of the seed.

174. The seeds of different plants exhibit the Numbers of greatest diversity in number, size, and figure. Sometimes they are few; in other instances very numerous. In one plant of white Poppy, Grew reckoned 32,000 seeds; and on the spike of a species of typha, he numbered 40,176 seeds; so that, upon the three spikes which one stalk of this plant bears, there are every year produced more than 120,000 seeds. (Anat. of Plants, p. 198.)

175. In figure, the varieties in seeds are so numerous as to baffle description; and, with respect to size, many are so minute as not to be visible to the naked eye, and others so large as to reach several pounds in weight. The minute corpuscles, which are held to represent the seeds of certain cryptogamous plants, have received particular names from different writers; but mere difference in size seems not, in an anatomical view, to afford any just reason for such distinctions.

176. The part at which the seed has separated from the ovary, is indicated by a small mark or scar, called by Malpighi fenestra; by Linnaeus hilum; and by Gaertner umbilicus. In some seeds, this scar is of considerable extent, and is the only mark that is visible; in other instances, there seems to be present a foramen in addition to the scar. All seeds, says Grew, have their outer coats open, either by a particular aperture, as in the bean C, fig. 21. (a) Plate XV., or by the breaking off of the cord, or by the entrance of the cord into the substance of the seed, as in those which have a shelly or stony covering. In the Bean, this apert-

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Of the Seed-ture is placed on the side; in the Chestnut, on the top; in the Gourd, at the bottom; and in each case, the point of the radicle is opposed to the aperture, and first pushes forth through it. (Anat. of Plants, Book I.) In many seeds, however, the radicle is not thus opposed to the umbilicus; but, according to Gaertner, is variously placed with regard to it; and in the seeds of the Apple and Pear, Malpighi considers no proper umbilical aperture to exist, but only an hiatus to be formed by the relaxation of the tunics, through which the radicle makes its way. (Anat. Plantar. p. 9.)

Varieties in its Form.

177. There can be no doubt, that, in every case, a connection subsisted between the seed and the ovary, during the formation of the seed; but this, in different examples, may have much varied. In all cases, an umbilical cord must have existed, and appears, in many examples, from inspection of mature seeds, to have been the only visible medium of connection. In the Bean, however, beside the umbilical cord, there are marks of a connection also between the coats of the seed and those of the ovary that contained it; so that the scar or cicatrix, in that and similar cases, is distinct from the umbilical aperture. The scar is the mark left by the separation of the tunics continued from the ovary; the foramen is the aperture produced by the separation of the umbilical cord. It will be afterwards stated, that the outer coat of the seed appears always to have originated from the inner coat of the ovary; so that it forms a sheath about the umbilical cord. If, therefore, as in the Bean, these coats are thick, and the umbilical cord short, then traces of the separation, both of the coats and of the cord, will remain on the seed; if, on the other hand, the coats are thin, and the cord more elongated, this latter will be closely invested by the former, and the umbilical scar will present the appearance only of a simple aperture, as is common to many seeds.

Opinion of M. Turpin.

178. A late writer, M. Turpin, regards the umbilical scar as consisting of three parts, viz. the proper cicatrix itself, in the centre of which he describes an aperture through which the nutrient vessels passed to the embryo, and near to it another smaller aperture, through which he believes the spermatic vessels to have passed. The former he calls the omphalode, the latter the micropyle; and declares, that he observed it in more than 1200 seeds. (An. du Mus. d'Hist. Nat. Tom. VII. p. 199.) Aware, however, of the fallacy of microscopical observation employed on such minute objects, we shall suspend our belief in the existence of this structure, until it receive confirmation from some other observer. As yet, we believe, no one has been able to share with M. Turpin the benefit of this discovery.

Regions of the Seed.

179. From the situation of the umbilicus, the several parts or regions of the seed have been defined. They are six in number. The part where the umbilicus itself is placed, is termed the basis, and the point at the opposite extremity, the vertex of the seed; the upper or back part is named the dorsum or back; and the part opposite to it the venter or belly; while the two lateral portions are called the sides (lateral). The point where the umbilical cord is inserted into the inner coat has been named the internal umbilicus. This point usually coincides with that of the external, but, from a change in the relative position of the parts during their formation, this coincidence is not always to be observed. Umbilicus, (Gaertner de Fructib. et Seminib. Plantar. Vol. I.)

180. When examined in its mature state, the seed coat is found to be composed of certain coats or tunics, which enclose a kernel or nucleus, that also consists of several distinct parts. At an early period of growth, while the parts are still green and succulent, two coats are easily distinguished; as in the transverse section of the bean, D. fig. 21. Plate XV.; in which the inner coat appears much thicker than the outer, and the radicle (b) is seen rising through it.

When these coats are stripped off, the other parts, its Nucleus, which form the nucleus, are brought into view. They consist, in the Bean and most other seeds, of two distinct parts, the lobes or cotyledons, as they have been called, and the radicle and plumule. These several parts can be seen only by separating the two lobes from each other, as is done in fig. 22., where the letters (cc) denote the cotyledons, (d) the radicle, in Dicotyledons, and (e) the plumule. Such seeds as have thus two cotyledons, are named dicotyledonous.

181. In many seeds, however, the part called cotyledon is single, and bears but a small proportion to the entire bulk of the seed. An example of this kind is presented in fig. 23., which represents a section of the seed of Canna Indica. The nucleus enclosed in its two tunics, forms, as before, the chief bulk of the seed, and in its centre appears an oblong body (f), in Mono-cotyledons, the cotyledon, at the base of which the mono-cotyledonate radicle and plumule (g) may be discovered. The little oblong body below, represents the cotyledon alone. Seeds, which have thus but one cotyledon, are named Monocotyledons; and to this division the seeds of wheat, barley, and all the grasses belong.

182. Some botanists have alleged, that several orders of the lower tribes of plants are entirely destitute of a cotyledon, and have given to such the title of Acotyledons. This title was formerly considered to apply to all cryptogamic plants; but the researches of the elder Jussieu and of Hedwig, are said to have proved it to be inapplicable to Ferns and Mosses; and the seeds of the Algae and Fungi have not yet been discovered. Others assert, that some seeds have more than two cotyledons, and such seeds they have denominated Polycotyledons; but others again choose to consider these appearances not as distinct cotyledons, but only as deep fissures, or divisions in two primary lobes—and hence conclude, that all seeds may be classed under the two divisions of mono and di-cotyledons. We are not competent to decide on the merits of these opposite opinions; but shall only observe, that they seem to be governed as much, at least, by preconceived views of system, as by unprejudiced observations of nature.

ARTICLE II.

Description and Structure of the Coats of Seeds.

183. Having given this general view of the several parts that compose the seed, we proceed now to a more particular description of their structure; and,

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Of the Seed, as the tunics come first into view, we shall begin with them. These tunics, in some seeds, are two; in others, three, in number. By Grew, they were named coats or covers; by Malpighi, secondine; and by Gaertner, testa and membrana interna. We shall speak of them in the familiar terms of the outer, the inner, and the middle coats, or tunics.

Outer Coat. 184. The outer coat or testa of Gaertner, is described as a constant and essential part of the seed. It existed before the period of fecundation, and is sometimes the only apparent covering possessed by the mature seed. Some seeds have indeed been considered to possess no tunic whatever; and have therefore, says Gaertner, been named accor; but in such seeds there existed a coat before they arrived at maturity, and its apparent absence has been inferred from its extreme thinness, or its condensation with the sides of the surrounding ovary. (De Fructib. Plantar. Vol. I. p. 132.) A distinguished botanist, however, Mr Brown, is said to have lately discovered two examples of seeds absolutely destitute of a covering, from their first appearance to their state of maturity. (Thomson's Annals of Philosophy, Vol. I. p. 319.)

In Structure. 185. In different seeds, this tunic possesses a very different structure, being in some thin and membranous; in others of a spongy or fleshy nature; and in others, again, it approaches to the consistence of leather or bone. But how various soever in this respect, it is always an entire tunic, and has no aperture but that of the umbilical foramen. Its colour is usually deeper than that of the other parts of the seed, and in this particular it presents every possible variety. It has rarely any connection with the nucleus, except in some monocotyledons. (Gaertner. Vol. I. cap. 9.) With regard to its origin, Malpighi describes it, in its earliest state in the Almond, as derived from the ovary itself, being composed of reticulated vessels, which spring from the surrounding organ. In other instances, it is thicker, and is distinctly seen to be cellular, as well as vascular; and in the Bean and Pea, little tubes are said by Malpighi to originate from the cells, and terminate by open mouths on the surface. (Anat. Plantar. p. 9.)

Pellicula. 186. Both Malpighi and Grew discovered, in some instances, a very thin membrane to cover this outer coat, which, according to Gaertner, may be found in most seeds, if the parts be scrupulously examined. Its structure is sometimes membranous, often downy, and sometimes mucilaginous; it possesses occasionally considerable thickness, and at other times is a mere pellicle; and thence has been named pellicula. It covers the whole seed, and does not ever separate spontaneously from it. (Gaertner de Fructib. &c. Vol. I. cap. 9.)

Arillus. 187. Besides this pellicle, another fine tunic named arillus, is sometimes observed on the surface of the seed, as in the seed of Euphorbia. It originates from the umbilical cord at the base, and extends more or less completely over the body of the seed. Its structure is very various, being sometimes soft and pulpy; at others, thin and membranous; and in others, forming a husky covering. It forms, in some instances, only a loose and partial covering; and in others, it invests the seed so closely and completely, that it can scarcely be distinguished from the outer coat itself. Both of the Seed in figure and colour it often varies greatly; but, like the pellicle before described, it is regarded rather as an accessory, than a necessary integument.

188. To the exterior coat of the seed, various appendages are sometimes attached, as down, wings, spines, hooks, all designed either as a defence to seeds, or to facilitate their dispersion. They are distinguished and described by the botanist; but are, in general, of too fine a texture to be made the subject of anatomical demonstration.

189. The inner tunic (membrana interna of Gaertner) is a common, but not constant part of the mature seed. It appears sometimes to be wanting, when in reality it is present. During the formation of the seed, it is frequently so attenuated, or coalesces so completely with the outer coat, that it cannot be properly distinguished. In its earlier state, it is represented by Grew as a very spongy and succulent body, and as thick and bulky as one of the lobes itself; but it dries and shrinks up as the seed approaches maturity, so that it is sometimes scarcely discernible. (Anat. of Plants, p. 47.) In the seeds of most plants, it closely invests the nucleus, but is easily separable from the outer tunic. In those of the Gramineae, where the bulk of the seed consists almost entirely of inorganic matter, no separation of this tunic from the contained parts occurs; but its inner surface is formed into a cellular tissue, in the cells of which the nutrient matter is lodged. In other instances, the inner surface is prolonged into processes, which penetrate into the nucleus, and intersect it in various directions.

190. This inner tunic does not, like the former, exist before fecundation, but is formed subsequently to it. It is composed of vessels and cellular tissue. The cells are commonly larger than those of the outer coat. It has no aperture, says Gaertner, not even an umbilical one; but resembles a shut sac, over whose external surface the umbilical vessels creep, and open, in an insensible manner, within its cavity. (De Fructib. &c. cap. 9.) The distribution of the vessels throughout the whole of this coat Grew compares to that in the leaf.

191. Beneath this inner tunic, Grew describes another fine membrane, which immediately invests the third coat, the lobes or cotyledons of the seed. In the Bean, it is exquisitely thin, and so firmly continuous with the lobes, that some dexterity is required to accomplish its separation. It is spread not only over the convex surface of the lobes, but also over the inner or flat surfaces, where they are contiguous, extending likewise over the radicle and plume, and so over the whole nucleus of the seed. It does not, like the other tunics, cease to grow in germination, but is augmented and grows with the organic parts. (Anat. of Plants, B. I. ch. 1.) This tunic may be regarded either as a covering to the nucleus, or as an actual portion of it, as Gaertner, who speaks only of two coats, seems to have considered it. It appears, however, more proper to regard it as the innermost coat, and thus to conclude with Grew that the covers in most seeds are three. (Ibid. B. IV. ch. 3.) The coat last described must, in that case, be considered as the middle tunic, being situated between the outer Of the Seed—One, and that which is continuous with the nucleus.

In many seeds, however, only two coats are distinctly visible.

Uses of the Coats.

192. The foregoing tunics not only contain the nutrient matter, and afford a mechanical protection to the organic parts, but seem fitted also, by their chemical constitution, to resist the operation of agents that might otherwise effect their decomposition, and that of the nucleus they enclose. From the experiments of Fourcroy and Vauquelin, on the tunics of certain seeds that grow in marshy situations, it appears, that, beside the usual ingredients of vegetable substances, there exists in them a compound, formed by a combination of tannin with a peculiar matter of an animal nature, in union with a vegetable acid. This combination of tannin with the matter just mentioned, renders these tunics insoluble in water, and enables them to resist putrefaction, although buried for long periods in the moist earth. The tunics of those seeds, which do not possess this chemical constitution, may, it is added, by their ligneous or horny texture, or by the oily matter with which they are penetrated, present similar obstacles to the action of decomposing agents. (An. du Mus. d'Hist. Nat. Tom. XV. p. 77.)

Article III.

Description and Structure of the Nucleus of the Seed.

193. We proceed next to describe the parts contained within the above-mentioned coats or tunics, and which constitute the nucleus of the seed. These parts, as already observed, consist of the radicle, the plume, and cotyledons, together, in most instances, with the nutrient matter destined to support their future growth. The three former bodies are completely organized, but the nutrient matter is wholly inorganic, varies greatly in quantity and proportion in different seeds, and is very variously situated with respect to the organized parts.

194. These parts, which, in the progress of their evolution, give birth to the new vegetable, derive their visible origin from a medullary point, that succeeds to the act of fecundation. By some, these organized parts have been called the corculum; by others, embryo; by others, fetus; and by others, plantula seminalis. The primary point or particle, from which they originate, may, with propriety, says Gaertner, be termed corculum, since it is the source and seat of vegetable life, and from it the whole vascular system of the embryo proceeds. In some instances, this corculum increases so little as to be scarcely visible even in the mature seed; or exhibits only a palish spot, which has been termed cicatricula. In others, it forms a roundish radicle, whose apex is free, and rises above the nucleus, but whose base is firmly connected with it. In others, again, the corculum is still more disengaged, enlarging at each extremity, and producing at one end the radicle; and separating at the other into the two lobes called cotyledons, between which the first bud or plume of the future plant is situated. From this varying growth of the corculum, an embryo, more or less perfect, is produced. When the embryo presents only a mere germinating point, it is stiled imperfect; when it exhibits a simple radicle, it is deemed incomplete; when it possesses both radicle and cotyledon, it is considered perfect; and when it consists of radicle, cotyledon, and plume, it is pronounced complete. (Gaertner de Fructib. &c. Vol. I. cap. 13.)

195. In the mature seeds of the less perfect plants, the embryo is altogether invisible until after germination, and even, in many other instances, its characters cannot be accurately traced. Its general figure is determined by that of the radicle and cotyledons, and is exceedingly various in different seeds. In size, it ranges from a minute point to that of a body of considerable magnitude. In consistence, it is almost always soft and herbaceous, but its radicle possesses sometimes a ligneous hardness. No seed contains more than one embryo, except in cases of superfection, of which Gaertner saw one instance in Pinus Cembra, a seed of which contained two embryos within one and the same cavity. (De Fructib. Vol. I. p. 168.) Malpighi also records a similar occurrence in a seed of Prunus Armeniaca; and the seeds of the Gramineae, as will afterwards be shown, are capable of evolving an indefinite number of embryos. Every complete embryo is said to consist of three distinct parts, beside cotyledons. These are the radicle, the stem, and the plume.

196. The radicle (radicula), called rostellum by Linnaeus, is the most constant part of the embryo, being found in some seeds, in which no other trace of that body can be discovered. In the seeds, however, of the less perfect plants, and even in those of some monocotyledons, no radicle is visible antecedent to germination. In some rare instances among dicotyledons, as in Nelumbo nucifera, no radicle exists; but, in germination, the stem first rises upward, and afterwards emits rootlets from its sides. (An. du Mus. d'Hist. Nat. Tom. XIII.)

197. The size of the radicle is very various, and so also is its figure, being either conical, cylindrical, filiform, or tubercular, &c. It always, says Gaertner, occurs solitary, except in Secale, Triticum, and Hordeum, to which alone, of all known seeds, three, four, or six radicles, properly formed, and distinct from each other, are furnished to each embryo. (De Fructib. &c. p. 169.) This plurality of radicles in the cerealia had before been remarked by Malpighi. M. Du Hamel describes the seed of Mistletoe (Viscum Album), as emitting numerous radicles like those of wheat. (Mém. de l'Acad. des Sciences, 1740.)

198. The stem (scapus) of the embryo is a continuation of the radicle, and connects it with the plume. It is frequently wanting altogether, nor, when it is present, can we fix precisely on the point where the radicle ends and the stem begins. What is called stem, descends frequently into the earth, and becomes a true root; so that every part of the embryo, situated beneath the cotyledons, might, without impropriety, be denominated radicle. The place of junction between the radicle and stem was called by Grew the coarcture, from its presenting often an evident degree of contraction; but M. Bonnet, and others, have given it the more appropriate name of the neck (collum) of the seed.

199. The plume (plumula) is the first bud of the Of the Seed, new plant. In seeds that possess but one cotyledon, it is very generally wanting; and, even in those which have two cotyledons, it is not unfrequently absent, or is at least concealed within the stem. In most of the latter sort of seeds, however, the plume is met with. It is placed on the top of the stem or radicle, and lies between the cotyledons, by which it is variously compressed and folded on itself. In the greater number of seeds it is not entire, but, at its free end, is divided into several pieces, all closely coiled together, like feathers in a bunch, and thence called the plume by Grew. In different seeds, its several little leaves vary much, both in figure, size, and number. The structure, both of the radicle and plume, will be most advantageously displayed in connection with that of the cotyledons.

200. Of the organized parts of the seed, the organs called by Grew lobes, or dissimilar leaves; by Malpighi, seminal leaves, or cotyledons, remain to be described. The cotyledons derive their origin from the embryo itself, of which they constitute a part. The seeds, however, of some tribes of vegetables, as before remarked, are held not to possess these organs; and in many others, the mass of nutrient matter has been confounded with them. When present, they are either simple or divided. The simple cotyledon is formed by the mere extension of the corculum, and is in truth scarcely distinguishable from the stem itself. The double, or conjugate cotyledons, are produced by fissures which usually divide that part of the embryo that is opposed to the radicle, into two or more equal portions or lobes. These lobes have, at first, the appearance of mere tubercles, and in many seeds they retain this form unchanged; but, in others, they gradually expand into lamellae, or plates, which augment in size, and finally exhibit the proper form of cotyledons. This form is very various, as likewise is the size of these organs. Sometimes they are so small as to be scarcely visible, and sometimes so large as to form the chief portion of the seed. Their substance is either thin, or thick, or turgid. Their colour is commonly white, but sometimes yellowish, purple, or green; the colour into which they all pass during germination.

201. Concerning the structure of the cotyledons, it may be said that, in the more perfectly developed seeds, they are formed of cellular tissue, through which vessels are everywhere distributed; and, as we have already remarked, they are everywhere covered by a fine pellicle, or coat, which prevents alike their adherence to the plume and to each other. This cellular structure of the cotyledon is well displayed by Grew (fig. 24. Pl. XV.) in a slice of the cotyledon of the recent bean; and it is easily seen in a thin slice of almost any mature seed, if it be held against the light after it has been soaked in water. This cellular structure extends into the radicle and plume, but in much smaller proportion, constituting, according to Grew, about 3/8ths of the plume, 3/8ths of the radicle, and 3/8ths of the cotyledon.

202. Through all the organs that compose the nucleus, vessels are distributed, by the medium of which a general communication is established among them. This vascular system is likewise exhibited by Grew in the dissection of a Bean (fig. 26. Plate XV.), in which the vessels are seen to branch off on each side from the radicle, and spread themselves, by innumerable ramifications, through the cotyledons. From the radicle, vessels also pass upwards to the plume. These vessels of the radicle are visible when a transverse section is made through it, as in fig. 27. E., in which they are seen to occupy the middle of that body. When the section is made higher up at the neck of the embryo, as in the same fig. F, then the central trunk, surrounded by several smaller fasciculi of vessels, passing to the different parts of the plume, is still more clearly exposed. In many seeds, however, the organized parts are so small that their general structure cannot be traced, except during the progress of their germination. We shall therefore defer the description of them, till we come to treat of their evolution; and shall then also go more fully into the structure of the parts just mentioned.

203. Within the cells of the cotyledon, in many dicotyledonous seeds, the nutrient matter, destined to support the future growth of the embryo, is entirely contained. In other instances, this matter is only in part received into those organs; and in the Gramineae, and other monocotyledons, it is often placed almost entirely exterior to the cotyledon. This matter is produced from a clear liquor that is secreted in the tunic during the formation of the seed. To this liquor Grew gave the name of albumen, from its likeness not only in appearance, but, as he conceived, in use also, to the white of egg in animals. By Malpighi, this matter, considered in connection with the tissue that contains it, is often called the flesh (caro) of the seed; and from its being sometimes situated around the embryo, it has been denominated perisperm by M. Jussieu. We follow Grew and Gaertner in the use of the term albumen; meaning to express thereby, not the primary animal compound to which chemists have of late assigned that term, and which is found but in few vegetables; but that compound substance which, whatever be its situation, quantity, or colour, constitutes the nutrient matter of the seed.

204. This albumen is a very constant part of the mature seed, but its proportion, in some seeds, is so extremely small, that the seeds in which this occurs have been termed exalbuminous; and, in a few instances, it seems to be entirely wanting. Its quantity, situation, and figure, in different seeds, are subject to very great variation. In the seeds of the Gramineae, where the embryo acquires only a very small size, the albumen constitutes almost the entire bulk of the seed, and is placed wholly exterior to the embryo. In the Leguminose, on the other hand, the embryo is more completely developed, and the whole of the albuminous matter is contained within the cotyledons. In beet (Beta), and many others, the albumen is partly received into the cotyledons, and lies in part exterior to them; and where this occurs, the embryo sometimes encircles the albumen, and is sometimes encircled by it. In Rheum, the embryo is placed in the centre of the albumen; in Rumex, and some others, it is applied on the side of it; in Atriplex, the long cylindrical embryo surrounds the albumen; in Boerhaavia, the embryo and its cotyle- Of the Seed. The albumen cover entirely the granulated substance of the albumen. (M. Jussieu, *An. du Mus. d'Hist. Nat.* Tom. V. p. 224.) In the Onion (*Allium cepa*), the embryo makes several curves within the substance of the albumen; and in dodder (*Cuscuta*), it is twisted around it in a spiral form; so that the relative positions of the embryo and albumen, as well as their quantity, proportion, and figure, are subject to endless variation.

Albumen of Wheat. 205. But however much, in these respects, the albumen may vary, it is always contained within an organized structure. Sometimes this structure is that of the cotyledon, as already exhibited in the Bean, fig. 24, the cells of which contain this albuminous matter. Where the albumen is placed exterior to the embryo, as in the seeds of Wheat, it is nevertheless contained in a cellular tissue. This is exhibited in fig. 25, Plate XV., copied from Leeuwenhoek, in which cells of an hexagonal form are seen to be filled with the albuminous particles that constitute the white matter or flour of that seed. This meal part of Wheat he describes as consisting of minute globules, enclosed in a kind of membrane so exquisitely thin as scarcely to be observed, within which the globules are contained, as it were, in cells. The globules appeared to be of different sizes, not perfect spheres, but having an indentation on one part, which led him to suppose that they were not formed by simple accretion, but by some mode of growth, and that "the membranes which enclose them in cells, must be provided with so many veins or vessels, that every particle of meal may have its separate vessel." He even conceived the globules themselves to be enclosed individually in a thin skin or shell; but this opinion he never brought to ocular demonstration. (*Select Works by Hoole*, Vol. I. p. 169.) It may, therefore, be presumed that, in this instance, his imagination went beyond the powers of his microscope. Similar observations on the albuminous part of Wheat have since been given by Mirbel; and Kieser and others have delineated the globular particles contained in the cotyledonous cells of the Bean and other seeds; so that whether the albumen be situated in the cotyledons, or be placed exterior to them, it is, in every case, contained in a similar and distinctly organized structure.

Varieties of Albumen. 206. In consistence, the albumen varies; it is said to be either farinaceous, fleshy, or cartilaginous; and it may exist in various intermediate states. The farinaceous kind is readily reduced to powder, and is dissolved by water into a viscous mass. The embryo is generally placed exterior to this species of albumen, as in the Gramineae. The fleshy albumen is more frequent. It is softer than the former, and dissolves by water into a gelatinous mass. It is often entirely contained within the embryo and its cotyledons, and yields the thick oil that is expressed from many seeds. Lastly, the cartilaginous species has a horny consistence, is difficulty soluble in water, and not easily reduced to powder. The embryo is never placed exterior to it, and when it contains oil, this is usually very thin. (*Gartner de Fructib.* Vol. I. cap. x.)

Uses of Albumen. 207. In many seeds, the albumen serves as a support and defence to the embryo as well as for nutriment. If it be removed previous to germination, as was done by Mirbel (*An. du Mus. d'Hist. Nat.* Tom. XIII. p. 157.), in the seed of the onion, and by Dr Yule (*Wern. Trans.* Vol. I. p. 591.), in different species of Gramineae, the embryo, though planted in a rich soil, and carefully tended, grows but feebly, and for the most part dies.

208. Besides the albumen above described, Gaert-Vitellus has revived the use of the term *vittellus*, but employed it to designate a very different part from that to which it was originally applied by Grew. The latter made use of this term to designate the inorganic matter of the mature seed, which, in the early stage of its production, he called albumen (*Anat. of Plants*, Book iv. ch. iii.); but it is employed by Gaertner to indicate a small membranous body, which, in many seeds, is placed between the embryo and albumen, and is closely connected with the former, but separates easily from the latter. The figure of this small body is described as being very various in different seeds. It is said not to rise out of the earth during germination; but, like the albumen, seems destined to afford nutriment to the embryo. It forms the chief bulk of the seeds of the Cryptogamia; and in those of the Gramineae, it represents a thin scale interposed between the albumen and embryo, to which, from its shield-like form, he gives the name of *scutellum*. (*De Fructib. Plantar.* Vol. I. cap. xii.) There can be no doubt that this scutellum of Gaertner is the little "conglobate leaf" first observed in Wheat by Malpighi, and which later writers have denominated the cotyledon of that seed. In the next section, its form and situation will be clearly displayed.

SECTION II.

Of the Structure of Monocotyledonous Seeds, as displayed in their Evolution.

209. All seeds have, by some botanists, been distinguished into such as possessed one or more cotyledons, and such as were entirely destitute of them; others maintain that every known seed possesses at least one cotyledon, and that no seed has more than two; and others again think there are some seeds which possess many cotyledons. It is not within our province to discuss the merits of these several opinions. We only beg to observe, that, in treating of seeds under the two divisions of Mono and Dicotyledons, we would not be understood to deny the existence of seeds that have no cotyledon, nor of others that possess more than two. We employ these words only as convenient general terms, under which the greater number of known seeds may be arranged.

210. Some seeds are so extremely minute, that, until lately, their existence was not clearly ascertained; and it is only during their germination that their general form and character can be detected. In many others, the organized parts are so small as to be scarcely capable of demonstration, except by following the progressive changes of form they exhibit in their evolution. We propose, therefore, to select, from each of the two divisions of Mono and Dicotyledonous seeds, an example or two of the successive appearances displayed in their evolution, which will, Of the Seed besides, form perhaps the best introduction to a knowledge of the structure of the mature plant. To the division of monocotyledons, the seeds of Mosses and Ferns have been referred, and with them, therefore, we shall commence our description.

211. At the end of March, or beginning of April, by Hedwig: Hedwig procured the mature capsules or ovaries of a species of Moss (Mnium hygrometricum), and opening them over pots of earth, prepared to receive them, the fine dust of their seeds fell out. For several days they exhibited a dullish appearance, scarcely visible; but on the 7th day the surface became green. On the point of a needle, several of the young plantules were now taken up, and, being immersed in a drop of water, they were examined with a microscope that magnified 62 times. Innumerable seeds were visible, which had already put forth a very tender white radicle on one side, and on the opposite side a very simple obtuse corpuscle, extremely pellucid, and at its margin of a light green colour. Of these parts, a representation is given in fig. 28, G. Plate XV., in which the little globular body in the centre denotes the seed; and the radicle and lobe or cotyledon are seen, in opposite directions, to spring from it. The little node or seed was of a dusky colour, evidently swollen by the imbibition of moisture, and on its sides were marks of rupture made by the shooting forth of the radicle and cotyledon: these organs were themselves covered by an appropriate tunic. Sometimes, instead of one lobe, two or three sprang from the seed, as represented by the letter H. of the same figure.

212. In three days more, a second radicle issued from the seed, and the cotyledon also became divided into branches, as represented in fig. 29. For the next eight days, nothing remarkable occurred, except that the green colour increased in intensity. The proper leaves of the Moss now began to spring, and many succulent threads issued from the root. By the month of October, the young plantule was so much grown, that the parts of fructification could be distinguished. Its appearance, at this period, is exhibited, on a reduced scale, in fig. 30. Towards the end of November, the parts of fructification were completely developed, and from them seeds were obtained, which vegetated when committed to the earth in the following spring. From some other species of Mosses he obtained similar results, so as to leave no doubt that these plants are propagated by seeds, which at first put forth a radicle and cotyledon. (Fundamentum Hist. Nat. Muscorum, Pars 2da, p. 54.) His discoveries have been confirmed by several other botanists.

213. In another order of the Cryptogamia, the Ferns (filices), the parts of fructification are placed on the back of the leaf, or frons, as it is termed by botanists. They there form clusters of small globules or capsules, which are secured in their place by a little scale. When the seeds are mature, the capsule bursts, and the seeds are scattered. Some observations were made on the germination of the seeds of several species of Ferns by Mr Lindsay. In the climate of Jamaica, no alteration was visible in the seeds of Polypodium lycopodioides until about the 12th day after they had been sown, when they put on a greenish colour, and began to push out their little germ in the form of a small protuberance: this germ gradually enlarged, and exhibited, according to his delineations, several whimsical shapes, which subsequent observers have not been able to recognize. At length the green surface of the plantules assumed the form of small scales (fig. 31, Plate XV.), which appeared of a roundish figure, and somewhat bilobate, as seen in the enlarged view below. From this membranous leaf, a small leaf of a different figure afterwards sprang, which was followed by others, and in three months the development was complete. (Linnaean Transactions, Vol. II. p. 93.)

214. With this last representation of the appearance of the germinating seed of the Fern, the observations of M. Mirbel coincide. He describes the seeds of the Asplenium creticum as producing, a few days after they are sown, a small heart-shaped cotyledon leaf, represented of its natural size in fig. 32. It is formed entirely of cellular tissue, but exhibits no appearance of vessels. After some time, numerous small threads shoot from its point, corresponding in office to the radicle of ordinary seeds; and at length a plume, in the form of a crook, is said to shoot from the same part. Gradually, the cordiform figure of the cotyledon disappears, and it seems as if made up of two lobes, from the middle of which the crook-shaped plume continues to grow. (Ann. du Mus. d'Hist. Nat., Tom. XIII. p. 71.) See fig. 33, Plate XV., and its enlarged representation below.

215. The germination of these minute seeds has also lately been observed by Dr Yule; and his account differs, in some particulars, from that of his predecessors. He describes the first appearance of the young plantule, as resembling a dark green point, which, when closely examined, exhibits the form of two seminal leaves, rising out of the seed, and gradually expanding to the diameter of more than a quarter of an inch. From a circular opening in these seminal leaves, the frond or permanent leaf arises, and is afterwards followed by a second. He regards the first leaves as cotyledons, within which the embryo is included, and from which it springs, as in dicotyledonous seeds. He notices also, the absence of vessels in these cotyledonous leaves, and the circumstance of their emitting minute rootlets, by which they derive nourishment, previous to the shooting of the true root. His observations have been given to the public, in the article "Filices," in a contemporary work, the Edinburgh Encyclopaedia.

216. In most of the seeds of this division, the cotyledon does not, however, appear above the soil during germination, but is retained within the coats of the seed, and consequently undergoes but little alteration in size. As an example of the evolution of a monocotyledonous seed, we shall select that of Wheat (Triticum hybernum), because its development has been studied with great care, and, in common with some others of the same natural family, it exhibits some striking peculiarities, which add greatly to its productive powers. The successive appearances exhibited in its evolution, have been given with great accuracy by Malpighi, who has carried its anatomy farther, in some points, than most of his successors. Of the Seed. In the earlier stages of growth, some very accurate representations of it have also been given by M. Poiteau, and Dr Yule has likewise obliged us with some valuable observations. From these different authorities, confirmed generally by our own observations, we shall endeavour to present a concise view of the structure and evolution of this very important seed.

Description of Wheat.

217. If we take a grain of Wheat, and examine its convex side, we observe, at its base, a small oblong body, fig. 34. Plate XV., lying in a semicircular depression, which is well defined through the tunics that cover it. These tunics are two in number, an outer one, to which the chaffy filaments at the vertex of the seed are attached, and which readily separates when moistened; and an inner one, which everywhere adheres closely to the cellular tissue that contains the albumen. If these two tunics be raised and thrown back, as is done in fig. 35, the little oblong body (k), with its semilunar appendage (i) placed behind it, are brought into view; and together, they constitute the embryo.

218. Let next a vertical section of another seed be made in the direction of the furrow that runs along its flatter side, and let this section pass through the embryo, as is represented in fig. 36.—we then observe the seed to be composed almost entirely of albumen (k), with which the embryo (l), consisting of minute convoluted leaves, is in close contact. The part of the embryo that is applied against the albumen is the cotyledon, which, on that surface, is convex, and on the opposite one concave.

219. In fig. 37, the entire embryo has been removed from its connection with the albumen, and a front view of it, considerably magnified, is there given, in which the letter o denotes the cotyledon, in the concavity of which the plume (n) is lodged, and (m) indicates the protuberances from which the radicles afterwards spring. If now, this same embryo be reversed, as is done in fig. 38, then the convex back of the cotyledon only is seen, with the extremity of the principal radicle at the base. It is this side of the cotyledon that was applied against the albumen; and its polished surface, says M. Poiteau, proves that it nowhere adhered by any organic structure. Gaertner also remarks, that the connection between these parts is not organic, but merely superficial—an observation that is true, as far as relates to the embryo itself and the albuminous matter, but not as applied to the tunics which envelope them; for, at the base of the seed, the inner membrane, which contains the albumen, appears to be continuous, as Leuwenhoeck remarked, with that which covers the cotyledon, being reflected from the albumen over the cotyledon, much in the same way as the pleura and peritoneum, that line the sides of the great cavities in animal bodies, are reflected over the viscera they contain. Such are the appearances presented by this seed antecedent to germination; let us next follow it through the several stages of that process.

220. After a seed of this species has been in contact for 24 or 30 hours, with the humidity necessary to its germination, its embryo becomes swollen, and when removed from the other parts, and moderately magnified, presents the appearance exhibited in fig. 39. In this figure, the radicle is rendered more pro-

Of the Seed. tuberant, and the fine tunic that invests it has undergone an alteration, being changed from a smooth, opaque, and solid texture, to one that is villose, transparent, and cellular. A vertical section of the same by Poiteau embryo, as exhibited in the next figure (40.), shows the elongation of the principal radicle (p) which caused the protuberance below, and the sprouting of the two lateral radicles (pp), which push forth more slowly on the sides. These three radicles soon force their way through the sac that envelopes them, which then forms sheaths around their origins: In the same figure, the letter q denotes the plume, consisting of several convoluted leaves, and resting on the cotyledon. In fig. 41, the appearance of the seed, in a stage a little more advanced, is exhibited. The plume (r) is now seen to have risen above the cotyledon (s), and the three radicles, surrounded at their origins by their proper sheaths, have greatly increased in length, and innumerable capillary rootlets are emitted from their sides. (An. du Mus. d'Hist. Nat. Tom. XIII. p. 383.)

221. The daily appearances exhibited in the evolution of this seed, as previously given by Malpighi (Anat. Plantar. p. 103.), accord well with the above representations of M. Poiteau; and he has noticed some additional particulars of considerable importance. On the first day of germination, he represents on the 1st the plume of the embryo as beginning to open, and day: the protuberances, which indicate the eruption of the three radicles, as beginning to form. The radicles, at this period, are completely enveloped in a membranous sac or involucrum; and the body of the embryo is closely connected with a "conglobate farnaceous leaf by which nutriment is administered." This conglobate leaf is the cotyledon before-mentioned, and its connection with the radicle and plume is well shown by Malpighi. In fig. 41. (L.) he exhibits a front view of the radicle and plume, as they appear when separated from the cotyledon; and at the letter K. of the same figure, a back view of the same body is displayed, in which the letter l' points to the mark or scar that denotes the place of separation. Malpighi believed these parts to be united with each other by a little node, hereafter to be described; but it is by the medium of vessels that this connection between the cotyledon and the other parts of the embryo is maintained; and by this route alone can the nutrient matter or albumen be conveyed through the cotyledon to the radicle and plume. To these vessels M. Bonnet gave the distinctive appellation of mammary: the union they form between the different parts of the embryo is so close, that, at this part, says Gaertner, the cotyledon, the radicle, and plume, form one undivided body. (Gaertner de Fructibus Plantar. Vol. I. p. 149.)

222. On the second day of germination, the exterior tunic of the seed, according to Malpighi, gives way; the plume rises upward: the radicles do not as yet pierce their investing sac, but this sac is turgid with juice, and is covered exteriorly by a fine white down; the cotyledon, also, at this period, is rendered moist.

During the third day, the cotyledon is quite tur-

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Of the Seed, gins to look green; the three radicles have pierced the enveloping sac, and are everywhere thickly covered with hairs; and above the two first lateral radicles, two small protuberances, v. z. fig. 43, the origins of two more radicles, are now seen to emerge, while the sac that envelopes them is observed sensibly to waste.

4th day:

223. When the third day has elapsed, the plume, enclosed in a fine transparent membrane, is still more elevated, and acquires a greenish colour; the protuberances of the two new radicles are more prominent, and the three former radicles have greatly augmented: the cotyledon is much softer, and as if milky, yielding, when compressed, a white and sweetish liquor.

5th day:

224. After the completion of the fourth day, the plume v., fig. 44, continuing to ascend, pierces the membranous covering x, and pushes into day a permanent leaf, green and convoluted, around which the membrane forms a sheath. Inferiorly, the three first radicles have greatly extended, and the two others yy, are much increased: the outer coat of the seed now begins to lessen, but still contains a sweetish liquor. M. Poiteau gives a section of the entire plantule about this period of its growth, which agrees very exactly with the figure of Malpighi. In this section, fig. 45, the plume a' is seen to have pierced the membrane b' that formerly enclosed it; the albumen c' is diminished; the cotyledon d' retains its situation and form; and the five radicles e'e' are nearly of a length, and covered with hairs.

6th day:

225. About the sixth day, the plantule, still invested by its sheath, begins to open and expand; the seminal tunics shrink, and the surface of the outer coat is corrugated. If these tunics are cut open, the cotyledon within is observed, in some parts, to be firmer than before, and has the appearance of a concave leaf; but in other parts, it is more vascular, and filled with juice, especially in that part near to the mammary vessels.

11th day:

226. After the eleventh day, these tunics still adhere to the plantule, but appear much wasted, and the juice they contain is mixed with bubbles of air; while the stem, forming many knots, and the radicles emitting innumerable rootlets, continually augment in size. Where the vegetation has been very active, the whole original contents of the seminal tunics are by this time exhausted, and, when compressed, they yield only a watery fluid.

227. After the lapse of a month, when the parts, already developed, are still farther advanced, new buds break out from the primary seat of growth and rise upward; and new radicles push forth and descend. So readily are these radicles produced, that sometimes, if the primary ones be removed, others in crowds spring forth; at the same time, new buds or shoots, protected in their proper sheaths, arise from the same part, and, surrounding the primary plantule, are borne upward with it. Of these appearances accurate delineations are given, and they may be observed in every field of growing wheat.

228. The foregoing descriptions of Malpighi are, in general, very correct, and his figures, though somewhat rude, exhibit, as usual, faithful delineations of the objects they are destined to represent. In one or two points, however, he has fallen into error, which, in the above statement of his opinions, to avoid confusion, we corrected as we went along. Thus, though he distinctly points out the "conglobate farinaceous leaf," as the organ by which nutrient is administered to the radicle and plume; he assigns to the sac that, in an early state, envelopes the radicles, the function of placenta; and even gives to the exterior tunic of the seed the title of seminal leaf. The true cotyledon, however (which never in this seed is produced into a seminal leaf), is the little conglobate body above mentioned; and the common tunics of the seed have no title to the appellation of seminal leaves. To this cotyledon, Gaertner, of Gartner, from its shield-like form, gave, as before observed, the name of scutellum. He held it to be characteristic of the graminaceae, and analogous to the organ to which, in some other seeds, he gave the name of vitellus. (De Fructibus Plantarum. Vol. I. p. 139.) But most later writers, as Jussieu, Smith, Brown, and Poiteau, have all restored to it its proper office of cotyledon.

229. M. Poiteau has gone even farther, and asserted the existence of a second cotyledon in this seed, and in the oat, which he describes as situated directly opposite to the former. (An. du Mus. d'Histoire Nat. Tom. XIII. p. 388.) In this instance, however, he has mistaken the rudiment of the second bud for a second cotyledon, as Dr Yule ascertained by tracing the growth of this supposed cotyledon from its first becoming visible, to its final development as a plant." (Werner. Transac. Vol. I. p. 594.) M. Mirbel considers the sac that invests the plantule of Mirbel to be the cotyledon of this seed; and this cotyledon to form the first ensheathing leaf. (An. du Mus. d'Histoire Nat. Tom. XIII. p. 148.) But, as already remarked, the cotyledon never, in this seed, rises out of the tunics; and, as Dr Yule observes, differs totally in situation, structure, and consistence, from the ensheathing leaf of the plantule.

230. A very remarkable peculiarity in this family of plants is their great productive power, as displayed in the indefinite number of new plants which we have seen to be evolved from one primary seed. Malpighi not only observed this peculiarity, but has described the structure from which it originates. He considered the radicle and plume of the embryo to be connected with the cotyledon, not by the mammary vessels, as we have stated, but by a little body which he called the umbilical node. In a section of the lower part of the stem of the plantule, made after the third day of germination, he delineates this node as situated at the junction of the radicle and plume, as represented by the letter f', fig. 46. Plate XV.; and describes it as solid externally, and softer and more medullary within. If a section of the same part be made on the fourth day, as in fig. 47, the stem (g') Malpighi of the plantule will be seen, says he, to spring from this node, from which also the radicles equally take their origin.

231. This peculiar property in the Gramineae, was of Leuwenhoek also observed by Leuwenhoek, though he seems not clearly to have apprehended the nature of the organs from which it proceeded. In the embryo of wheat he describes three points, from which not only Of the Seed three distinct radicles spring; but they are also, he adds, "the beginnings of three several spires or stalks of wheat; so that from every grain of wheat (which is well worthy of observation), there will arise not merely a single stalk, but three distinct ones, which are formed in the seed itself." Select Works by Hoole, Vol. I. p. 169; and in Vol. II. p. 289, are to be found similar observations on the seeds of Oats, Barley, and Rye.

232. By M. Mirbel, the umbilical node of Malpighi is considered as a fleshy knot (un nœud charnu), by the medium of which the plumule and radicle are united. The lateral radicles, which issue from it, he regards as distinct in their nature from the primary one, and as resembling those which spring from knots in the stem; he therefore names them articulare roots, les racines articulaires. (An. du Mus. d'Hist. Nat. Tom. XIII. p. 149.) According to Dr Yule, however, this fleshy knot is to be considered as a tuber, analogous to the tuberous substance, interposed between the bulbs and roots of the Liliaceae and other monocotyledonous tribes; and which is destined to produce an indefinite number of young plants, a greater or less number of which are subsequently evolved by the joint agency of the roots and leaves. The "articulate roots" of M. Mirbel he regards as in reality young plants, the roots of the Gramineae being invariably fibrous. It is by means of these lateral shoots and their tubera, that bushes, consisting of from sixty to several hundred stems, are sometimes seen to originate from one seed.

233. The above important peculiarities in the germination of the seeds of the Gramineae, are very conspicuously displayed by Dr Yule in the three figures which we have copied from his Memoir. In fig. 48. Plate XV. Dr Yule represents the embryo of wheat as it appears when detached from the albumen, a short time after germination has commenced; the ascent of the plume covered with its membrane, and descent of the three primary radicles, which have pierced their containing sac, are clearly exhibited, and the letter h' points to the little cotyledon, placed at the junction of the two parts just mentioned. In fig. 49. the germination of the same seed is shown in a more advanced stage; the plume (r') has now risen to a considerable height, and pierced the investing membrane; and at k' a second bud or plume (which M. Poiteau mistook for a second cotyledon), is seen to shoot from the tuber like the first: the letter t denotes the seminal tunics. At a still more advanced period, four young plants, m' m' m' m', fig. 50. of the second month, with their sheaths in part withered, are seen to have sprung from the same part; but the two seminal tunics of the seed, exhausted of their contents, still remain attached, as indicated by the letter n'. (Wernerian Trans. Vol. I. p. 589.)

234. The description given above of the evolution of wheat is applicable, with little variation, to the seeds of all the cerealia. The seed of the Oat emits from four to six radicles, all of which break through their enveloping sac at the same place, and thus appear to be contained in one sheath; such too is the case with Barley, the plume of which extends beneath the seminal tunics, and pushes out at the vertex of the seed.

235. This peculiar constitution of the seeds of the Gramineae, is attended with important advantages in their culture, and explains the source of their great productive power. A single grain of Barley was observed by Du Hamel to have produced 200 ears, each of which yielded 24 grains; so that one single seed planted in a good soil, has produced 4800 grains. Curtis and others, by transplantation of the several plantules of Wheat, obtained still higher returns from single seeds. For the same reason, these plants are better enabled than others to resist the injurious effects of accident or disease. If a seed, says Dr Yule, be buried under a stone or lump of indurated clay, the seminal plantules cannot shoot upward; but stems are then sent off in a horizontal direction, until they can effect their escape upward. Sometimes it happens, that a small insect (Musca pumilionis) deposits its egg in Wheat, and the grub is lodged in the very centre of the stem, just above the root, by which the stem is invariably destroyed, and the root so materially injured, as to prevent its throwing out fresh shoots on each side, or stocking itself, as the farmers term it. Nevertheless, the plants thus attacked are not permanently injured; for, in the instance where these depredations occurred, the crop of Wheat was good, and the ears large and fine through the whole field; so that these injured plants, by the production of lateral shoots, yielded an abundant crop. (Lin. Trans. Vol. II. p. 76.)

236. In the germination of other monocotyledonous seeds, a similar succession of phenomena present themselves, with the exception of those which relate to the multiplication of so many individuals from a single seed, and which seem to be peculiar to the Gramineae. In all, the radicle first shoots forth, and the plume soon follows; the cotyledon is commonly of small size, and is retained within the tunics. As the embryo grows, the albumen is taken up and conveyed through the cotyledon to the young plantule; and, before the albumen is exhausted, the embryo is enabled to draw its nutriment from the soil in which it grows.

237. In many instances, it appears, that the primary radicle of these seeds, after a short time, becomes dry, and falls off, and is replaced by a great number of secondary rootlets. M. Poiteau regards this last circumstance as common and peculiar to monocotyledonous seeds. He has remarked it in many hundred palms, not one of which had a descending or tap-root. No plant in the numerous family of the Liliaceae is said to possess such a root. The radicle of the Cyperaceae does not, perhaps, perish so soon, but it does not continue long. This premature and constant destruction of the radicle he considers as the cause of the bulbs and truncations which occur, particularly in the Liliaceae; for the lateral roots not being capable of receiving all the descending sap, it collects at the lower part of the stem, and occasions these different enlargements. (An. du Mus. d'Hist. Nat. Tom. XIII. p. 392.)

238. The effects which thus succeed to the spon-

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Of the Seed. Taneous destruction of the radicle, occur partly in other plants, in which the first radicle is naturally permanent, if it be artificially removed. Du Hamel found, that, if the extremity of permanent radicles were cut off; lateral rootlets were produced; that even mechanical obstruction to the descent of the radicle frequently gave rise to divisions in it, and the production of these lateral rootlets. He ascertained, also, by experiment, that roots extend invariably, not by an elongation of parts already formed, but by new matter added to their extremities; and hence it is, that roots, whether ligneous or herbaceous, do not elongate, if even the smallest portion of their extremity be cut off. (Phys. des Arbres, Tom. I. p. 83.) The results of observations on the growth of Carrots, in different soils, by Mr Knight, correspond with those of M. Du Hamel.

SECTION III.

Of the Structure of Dicotyledonous Seeds, as displayed in their Evolution.

239. From the greater number of seeds which have two cotyledons, the phenomena of their evolution may be expected to exhibit at least as great variety as those of the division last described. In different species they differ in this respect as much from one another, as they do from monocotyledonous seeds. Some seeds of this class raise their cotyledons above ground during germination; in others, these organs are wholly retained within the tunics. Of each of these modes of evolution we propose to give an example, selecting, as before, those seeds which have been most accurately observed, or which, by the forms they exhibit, seem best calculated to illustrate the general laws, by which their evolution is accomplished.

240. In the seeds of this division the embryo is commonly much more completely developed than in those of the class last described; so that the several organs of the plantule become distinctly visible. The radicle and plumule are readily distinguished, and the cotyledons are frequently so large as to form nearly the entire mass of the seed. Within the cotyledons, the albuminous matter provided for the nutrition of the embryo during its evolution, is often entirely contained; and these organs, as before remarked, rise sometimes out of the earth, increase greatly in size, and, after a certain period, decay. In other instances, no increase in size, nor elevation above the surface, occurs; but, like the greater number of monocotyledons, they remain beneath the soil, and yield gradually their nutrient matter for the support of the embryo. Even in plants of the same natural order, the Papilionaceae, for example, some, as lupins, says Dr Smith, raise their cotyledons into the air and light; while others, as lathyrus, retain them under ground, concealed within the tunics of the seed. As an example of the latter, we shall give from Malpighi an abridged account of the successive appearances exhibited by the common pea (pisum), which, in its evolution, approaches, in some respects, to that of the seeds last described.

241. The figure and size of this seed are familiar to every one. After being placed for a day in circumstances favourable to its germination, it is much increased in size; its outer coat is rendered softer, and becomes more white and thin; the umbilical aperture continues closed, but near to it an irregular opening or laceration is visible. If the outer coat be now stripped off, the nucleus comes into view. It is seen to consist of two distinct parts or lobes, which are the proper cotyledons of the seed. These cotyledons are closely invested by the inner tunic; externally they have a convex surface, but internally, where they are in contact, their surfaces are nearly plain. Between them, in a small depression formed in their substance, lies the plumule; it is composed of a number of yellowish leaves, folded on each other, and bent inward, and is united by a little curved stem, to a small white conical body, the radicle. These appearances are exhibited in fig. 1. Plate XVI., in which one of the cotyledons has been removed, so that the inner surface of the other, together with the plumule and radicle, are fully brought into view: the letter a denotes the cotyledon, b the plumule, and c the radicle. This radicle at its neck, or point of junction with the stem, sends off on each side a little stalk or pedicel to each cotyledon. In the above figure, one of these pedicels has been cut through, and the other, that remains attached to the cotyledon, is concealed behind the plumule. It is by these pedicels alone that the two cotyledons are connected with each other.

242. When the second day of germination is completed, the cotyledons are rendered more tumid, the tunics give way, and the radicle begins to protrude. Soon after, the cotyledons separate a little, and become somewhat concave internally. After the third day, the radicle has pushed out through the tunics; it is white, except at its point, which is more deeply coloured, and it emits on all sides fine capillary rootlets; the cotyledons are now farther separated, and by degrees the stem of the embryo, with its curved plumule, are disclosed.

243. About the fifth day, the stem (d. fig. 2.) mounts upwards; it is white, and bears on its summit the plumule (e) still curved, and now becoming green: the stem now also begins to exhibit the marks of knots at particular parts: the radicle (f) is farther advanced, and small protuberances, the origins of future rootlets, appear on it: the cotyledons (g) retain their place, are turgid and solid, and still surrounded by the lacerated tunics.

244. At the close of the seventh day, the plantule is much more advanced; the knots on the stem (h. h. fig. 3.) are quite distinct, and its apex is furnished with broad green leaves, but which are not as yet unfolded. The substance of the cotyledons is still solid, and when compressed, yields a bitterish juice: the radicle is much elongated, and has emitted numerous rootlets.

245. After the ninth day, the plantule is completely formed: its stem (i. fig. 4.) is now erect, and the leaves of the plumule (k) are expanded: the cotyledons (l) are reduced in size: and the radicle (m) or root, as it may now be termed, with its numerous rootlets, is greatly augmented. Every part of the plantule, except the cotyledons, continues daily to increase; at 246. The progress of evolution in those seeds that raise their cotyledons above the earth, is exhibited by Malpighi in that of the Gourd (Cucurbita). This seed is of an oblong figure, and has a flattened form. It possesses three distinct coats or tunics: the outer one is thick, tough, and coriaceous; the middle one thin, membranous, and of a greenish colour; and the inmost is that transparent colourless pellicle that closely invests, and is inseparably connected with, the cotyledons of the seed.

247. After this seed has been made to imbibe moisture, the outer and middle tunics readily separate, and expose the nucleus, which is seen to consist of two leaf-like cotyledons, which have no connection with each other, except by the medium of the little conical body, or radicle, at their base. The size and figure of these cotyledons, and the situation of the radicle that connects them, are represented in fig. 5, Plate XVI. Their external surface exhibits to the naked eye prominent lines which indicate a vascular structure, the vessels of which proceed from the radicle at their base. They are commonly five in number, and from their main fascicular trunks, ramifications are produced, which, in their distribution, form a finely reticulated appearance over the whole organ. On their inner side, the cotyledons are quite plain, and closely applied against each other, but, as already remarked, are nowhere connected, except at the base. This surface is displayed in figure 6, in which the great vascularity of the organ is rendered more apparent. It is between the two cotyledons that the plume, consisting of minute convoluted leaves, is lodged and cherished. In figure 7, a part of the nucleus of this seed is represented a little enlarged, and the two cotyledons have been removed at different places by transverse sections, to show more clearly the situation of the radicle and plume. The letter n denotes the place from which one of the cotyledons has been removed, so as to bring the plume (o) into view, and p points to the conical radicle below.

248. When this seed has been twenty-four hours in circumstances favourable to its germination, it is rendered tumid, and the umbilical aperture at its base is enlarged by the swelling of the parts within; the cotyledons become turgid, and the plume is augmented in size. After the second day the outer coat is much softened, the middle one appears as if torn and decaying, and all the parts within still farther augmented in size. During the third day, the colour of the outer tunic becomes darker; the cotyledons are more swollen; their vessels more conspicuous, and the radicle pushes out through the umbilical aperture.

249. When the fourth day has elapsed, the plantule is still retained within the tunics, and if these be now removed and examined, the middle one is found to be dry and thin; the cotyledons (q, fig. 8.) are whitish, soft, and flexible, but the vessels on their surface are much more distinct; the radicle (r) is elongated and covered with down, as likewise is the stem (s). At the top of the radicle, a protuberance is seen, which is white and soft; and farther down appear several smaller tumours, indicating the places of rootlets about to break out.

250. About the sixth day, the cotyledons g, fig. 9, emerge from beneath the tunics, representing the "dissimilar leaves" of Grew, and the "seminal leaves" of Malpighi, but which we shall, in future, denominate cotyledonous leaves. They are thick, soft, and a little separated from each other; their position is pendent; their colour yellowish; they are very vascular, and between them the plume is still concealed. The radicle (r), at this period, is much elongated, and rootlets everywhere spring from its sides; the stem (s) is also lengthened and curved, and, in common with the radicle, is everywhere covered with a white curling down.

251. Towards the ninth day the cotyledonous leaves (q, fig. 10.) assume an erect position. At their points, they are still yellowish, but elsewhere green, and their cellular tissue is filled with a greenish yellow juice; they begin to separate a little, but still entirely conceal the plume. The stem (s) at this period is greatly elongated, and its lower extremity has become green; the protuberance that existed at this part is greatly lessened; and below it, the radicle (r) is continued, from which numerous rootlets, covered with fine capillary productions, break out.

252. During the following days, the cotyledonous leaves continue to enlarge, the stem to elongate, and the plume to augment in size; but it is not yet unfolded. About the twenty-first day, the development of the plantule appears to be completed. A representation of its foliage at this period, is given in fig. 11.; the cotyledonous leaves (q) have now reached a great size, are of a deep green colour, and very vascular; they rise, by a short pedicle, from the summit of the stem. On each leaf, seven fasciculi of vessels are visible, which, beyond the middle, terminate in a net-work, from which is produced the cellular structure that contributes to form the breadth of the leaf. In the axil, formed by the cotyledonous leaves, the plume (t) lay concealed; it is now disclosed by the removal of one of those leaves. At first, the leaves of the plume are curled and convoluted, but afterwards they expand, and their figure is then seen to differ entirely from that of the cotyledonous leaves; they have notched margins, and their surface is covered with down. In this manner the young plant continues to increase, and acquires at length its full magnitude, in the progress towards which the cotyledonous leaves waste gradually, and finally fall.

253. The seeds of the Radish (Raphanus), of the Evolution Lettuce (Lactuca), and of the Kidney-bean (Phaseolus), are represented by Malpighi as exhibiting, in their evolution, a similar succession of appearances. In all these seeds, and in many others of this division, the radicle first pierces the seminal tunics; next the cotyledons come into view, and assume generally the form of leaves, between which the tender plume is for a time concealed, and at a later period is disclosed. In different seeds, however, the forms of these organs, and the periods of their successive evo-

VEGETABLE.

Of the Seed, I. tution, are subject to the greatest variation, not only as relates to the species of seed, but to the soil, the climate, and season in which it is destined to grow.

Internal Structure of the Pea: Having thus surveyed the changes in external form, which the germinating seed exhibits, we shall conclude our description by a display of the peculiarities of its internal structure. This we shall find to consist entirely of vessels and cellular tissue, variously proportioned and combined. In a longitudinal section of the radicle of the Pea, in an early stage, Malpighi represents it, as in fig. 12, to be composed entirely of cellular tissue exteriorly, in the centre of which the vascular system, separating at the top into three divisions, to supply the plume and cotyledons, is placed. A similar section of the radicle (fig. 13), on the seventh day, exhibits corresponding sections of the rootlets it puts forth, which are seen also to consist of cellular tissue, and of vessels that come off from the central fasciculus of the radicle.

255. The stem, when about a month old, is composed of a thick bark formed of cellular tissue, within which are two rings of vessels, as seen in the transverse section, fig. 14. The inner ring (v) is said to consist of sap and spiral vessels; and exterior to this, a zone of vessels (w), yielding a peculiar juice, is said to be placed. In some very thin slices of the stem of the pea, viewed through a microscope of considerable power, the arrangement and distribution of the vessels and cellular tissue appeared to us as represented in fig. 20. The centre of the stem was occupied by cellular tissue, round which was a zone of vessels (v), forming four principal fasciculi. Exterior to this zone was a small ring of thickened cellular tissue, and beyond this, the proper cellular substance of the bark. Near the circumference of the stem were four larger fasciculi, which may probably be considered as the "proper vessels," while those near the centre may be deemed the sap-vessels.

256. In the plantule of the Gourd, a similar structure is observable. Fig. 15, exhibits a longitudinal section of the plume and radicle of that seed, considerably magnified, as they appear before germination, and shows the position of the vessels x, as they pass up towards the plume y. In the next figure (16.), a similar section of a radicle, on the second day of germination, is shown, in which the vessels that form the rootlets are seen to originate from the fasciculi that exist in the radicle. In figure 17, is represented a longitudinal section of the stem and radicle of the same plantule on the ninth day. In the stem, the vessels are disposed in a circle that surrounds the pith; but as they descend towards the root, they approach each other, and give off ramifications to form the rootlets. In a transverse section of the stem, on the 21st day, Malpighi describes it as hollow in the centre, fig. 18, around which six fasciculi of vessels are disposed, and the intermediate portion is occupied by cellular tissue. Hedwig, however, and Kieser, enumerate not fewer than ten fasciculi of vessels in the stem of this plant, some of which are placed next the pith, and others near to the bark.

257. To these representations of the structure of the Pea and Gourd by Malpighi, we shall add that of the Bean, in its early stages, as delineated by Grew, who has traced the distribution of the vessels in the radicle and cotyledons with great minuteness. In fig. 19, is exhibited a vertical section of a young Bean, which is made to pass through the cotyledons, the plume, and radicle. From the extremity of the radicle, the vessels ascend in fasciculi to the neck of the plantule, where they are seen to diverge towards each cotyledon, and ramify through it, while a central vascular portion is continued to the plume. In fig. 21, the vascular and cellular structure of the germinating Bean, at an early period, are shown in conjunction, in a highly magnified representation, presented here in a reduced size from Grew. In this figure, a' denotes the cotyledon; b' the enveloping tunics; c' the cellular tissue; d' the vascular system continued from the fasciculus e' in the radicle, and ramified through the substance of the cotyledon; the letter f' points to the plume, which also receives vessels from those of the radicle; and g' indicates a depression in the cotyledon, in which, antecedent to germination, the plume was partly lodged; a similar depression existed in the other corresponding cotyledon.

CHAP. II.

THE ANATOMY OF THE MEMBERS OF VEGETABLES.

Section I.

Of the Structure of the Stem or Trunk.

Article I.

Of the Stem in Herbs.

258. In the foregoing chapter we have traced the successive changes of form which the seed exhibits in its progress to constitute the perfect plant; we have next to display the structure of the plant itself, in its more remarkable varieties and forms. The leading features of this structure have already been laid before the reader, when discoursing on the common textures of plants; it remains now to exhibit individual examples of it, as they occur in the several members of the trunk, the branch, and the root.

259. We have already noticed the very striking difference in the proportion and arrangement of the elementary organs, which obtains in different plants. While in some, the component textures are perfectly distinct from each other, in others, they are completely blended together; so that the characteristic distinctions of pith, and bark, and wood, are entirely lost. M. Desfontaines, as we remarked, has sought to connect this diversity of structure in the stem with certain peculiarities in the form of the seed; but it will appear, as we proceed in our descriptions, that such limitations and circumscriptions are perfectly arbitrary; and that Nature does not move by saltations, as the systems of naturalists would prescribe; but by a progress so gradual, and advances so continuous, that the lines and boundaries, which denote the perfection of artificial classification, are, in truth, but so many evidences of the immaturity of natural knowledge. In the case of Ferns, the structure of whose seeds has been displayed in a preceding section, we have a striking example of the insufficiency of this theory; for, while the stem possesses that simplicity of structure, which is said to appertain only to plants that spring from monocotyledonous seeds, the seed itself appears, from the observations of Dr Yule (214.), to belong clearly to the division of dicotyledons. Without any reference, therefore, to the form of the seed, we shall exhibit the structure of the stem and trunk of different plants, as they appear on dissection, beginning with the more simple, and proceeding gradually to the more complex forms.

260. Botanists employ different terms to distinguish the different kinds of stems or stalks that support the leaves, and the organs of fructification. These are the stem (caulis), which is considered peculiar to herbaceous plants, and the trunk (troncus), which is proper to herbs and trees; the straw (culmus), which is the appropriate stem of the grasses; and the stalk (scapus), which differs from the other varieties in bearing only flowers, but not leaves. For the peculiarities in external form and character, which distinguish these several kinds of stems, as they occur in different species of plants, we must refer to the writers on botany; and shall proceed to exhibit a general outline of their internal structure.

261. Perhaps there is no plant in which the simplicity of vegetable organization is more clearly displayed than in the Sugar-cane, which belongs to the family of Gramineae. In its stem or culm, the cells and vessels are comparatively large, retain much of their more perfect forms, and are quite distinct from each other. When treating of the cellular tissue (82.), we referred to the cells of this plant, exhibited in the very thin transverse slice, fig. 22. Plate XVI., as illustrative of their hexagonal figure, and of their being bounded, on every side, apparently by a single membrane. In some parts, when the observer is viewing these cells through the microscope, some of them appear quite transparent, from the upper and lower bounding membranes being entirely removed, and the light, in consequence, being freely transmitted; but in others, one or both of these membranes remain, and, though they are exquisitely thin, yet, when viewed by a strongly reflected light, a degree of refraction seems to be produced; which communicates to the surface of the membrane an irregular appearance, such as it has been attempted to express in the darker cells of the same figure. The deception that arises from viewing two layers of these cells in conjunction, which imparts the appearance of double sides, as in fig. 23, was before noticed; and the longitudinal appearance of the same organs, as seen both in a single and double series of columns (figures 24. and 25.), was at the same time described.

262. It is through this cellular structure that the vessels, which constitute the other component part of the culm of this plant, are distributed. They occur in fasciculi, which, towards the centre, are placed at considerable distances from each other, and preserve a symmetrical arrangement; but nearer to the circumference, they are more numerous, and their distribution is much less regular. In fig. 26. Plate XVI., a very thin transverse slice of this plant is exhibited, in which this regular disposition of the vessels at and near the centre (k'), and their crowded state near the circumference (i'), are well shown; the cells, too, at the centre, are larger, and have a more perfect form than those near the circumference of the figure. In fig. 27., a very thin longitudinal slice of this same plant is delineated; it is considerably magnified; the letter l' denotes the cellular tissue, and m'o'f' two fasciculi of vessels which ascend through it.

263. In the Palm, which, though belonging to the division of trees, we shall notice in this place, a similar disposition of the elementary organs is observed; but both the vessels and cells are smaller than in the Sugar-cane, and the fasciculi of vessels are also much more numerous. This structure is exhibited in the transverse section of the trunk of the Palm, fig. 28., in which the dark spots indicate the vascular fasciculi, and the whiter portion the cellular tissue. As before observed in the Sugar-cane, the vessels are seen to be less numerous at the centre than at the circumference, where they are much crowded together, and very irregularly distributed, in consequence of the peculiar mode in which the growth of these trees is accomplished.

264. In fig. 29. of the same Plate, we have also copied from M. Destontaines a portion of the longitudinal section of the trunk of another species of Palm (Dracaena draco), which displays more clearly the irregular direction which the vessels take in the lax cellular tissue through which they are distributed. It was before remarked, that these plants do not naturally produce branches; but that their vascular system is expended wholly in the production of leaves at their summit, and their trunk is perfectly cylindrical. If, however, the top of the plant has been cut off, or broken by accident, a division into branches is said to take place. (Mém. de l'Inst. Nat. Tom. I. p. 486.)

265. In the stem of Asparagus, the elementary organs possess an arrangement similar to that of the Palms; but in the progress of its growth, branches are given off continually, and consequently the stem diminishes in size as it ascends. In fig. 30., is given a vertical section of a part of the stem (a) of this plant, at that period of growth in which it is usually brought to table; the buds p'p'p', protected by the imbricated leaves, present a very beautiful appearance. At each place where a bud springs, a part of the vessels of the trunk go off to form it, and are finally expanded in its production; the diameter of the trunk above is consequently diminished, and the more central vessels are continued on, to be successively employed in a similar manner, till they terminate in a bud at the apex. We have thus an example where, though the elementary organs are uniformly distributed, as in Palms, yet, in consequence of the production of lateral branches, the diameter of the stem continually diminishes, and assumes the form of a cone, in which it differs from that of the Palm and Sugar-cane.

266. As in these plants the ligneous and cortical textures are uniformly blended together through the entire stem, it must be presumed that the sap-vessels and proper vessels are everywhere associated. This fact is accordingly pointed out by Malpighi as occurring in several species of the Gramineae, who, as we before remarked (62.), delineates a proper vessel as existing in each fasciculus of sap-vessels.

267. The next variety of structure we shall notice, is that of certain herbaceous plants, in which the proportion of cellular tissue in the stem very much exceeds that of vessels, and in many of their characters they come near to the plants last described. In the sections already given (figures 18. and 20. Plate XVI.) of the stems of the Pea and Gourd, the greater portion of the stem is seen to be made up of cellular tissue, but several fasciculi of vessels are dispersed through it. In fig. 31. Plate XVI., is a transverse section of the stem of the Gourd, of its natural magnitude, copied from Hedwig, in which the dark spots indicate the relative positions of the ten fasciculi of vessels that are observed in this plant. In fig. 32., a small portion of the preceding section, comprehending only two fasciculi of vessels rr', and highly magnified, is exhibited; the vessels are seen to be of different sizes, and, by their enlargement, they press upon and diminish the size of the neighbouring cells; the cells themselves are also of different sizes; in some parts, as denoted by the letter q', they are comparatively large. Their figure is generally hexagonal, though not always regularly so; and near to the vessels, they exhibit various irregular shapes. A very fine cellular tissue, placed exterior to the outer range of vascular fasciculi, forms the cortical texture of this stem; and from the succulent cuticle jointed hairs of various sizes are seen to spring; the centre of the stem is hollow. (Fundament. Hist. Nat. Muscor.)

268. The stem of this plant has been examined with great minuteness by M. Kieser, who has represented, in several sections, both transverse and longitudinal, its appearance in different parts, and at different periods of its growth. The number of fasciculi that exist in the mature stem he makes, with Hedwig, to be ten; but the number of vessels in each fasciculus varies at different periods, and even in the different parts of the same plant. In a mature plant, the number in each fasciculus, near to the summit, does not exceed six or seven; below the first knot from the top they are more in number; below the second knot, they amount to nineteen; and they increase in number in the next internodal space. In the centre of the stem, there are twenty-three vessels in each fasciculus; and near to the root, when examined in autumn, they amount to twenty-nine. In the trunk of the root, ten fasciculi of vessels may also be reckoned; but in the principal rootlets only four fasciculi are observed, each of which contains thirty-seven vessels.

269. The size and general characters of these vessels are represented as varying with age, not less than their numbers, and hence they have different forms in different parts of the same plant. At an early period, when few in number, they are very small near the summit of the plant, and consist only of simple spiral vessels; in a later period, and lower down on the stem, they are of larger size, and some of them exhibit the characters of annular spirals; in the third internodal space, their size is still greater, and two or three of them are now transformed into punctuated spirals; and still lower on the stem, the number of punctuated spirals is increased. In the centre of the mature stem, six large punctuated spirals are visible, and near to the root, in autumn, of the twenty-nine vessels that compose each fasciculus, twenty-three are punctuated spirals, and only six simple spiral vessels are now to be seen. The characters of these vessels now also approach to those of arborescent plants; their sides are thickened, and their transparency is almost lost, and the cavities of some of them are filled by membranous vesicles, which form within them a sort of cellular tissue. In the root, at this period, the simple spiral vessels have altogether disappeared, and only punctuated spirals, smaller than those in the stem, can be discovered. This successive disappearance of the simple spirals, and augmentation in the number of the punctuated variety, is urged by M. Kieser as a proof of the transformation of the one into the other during the progress of vegetation. No mention is made of the existence of proper vessels in these fasciculi; and the representations of the cellular tissue, of the ligneous texture, and of the bark, correspond with those given by Hedwig. (Mém. sur l'Organisat. des Plantes, p. 134.)

270. In the stem of the Gourd, as thus described, we observe an arrangement of parts in many respects according with that of the Sugar-cane. In both, the cells are large, and their figure is well preserved; and the vessels are distributed in distinct fasciculi through the cellular tissue. In the Gourd, however, the vessels are fewer in number, and do not suffer that displacement, during the progress of vegetation, which those of the Cane experience. In neither plant are the vessels so numerous, or so situate, as to compress the cellular tissue into transverse partitions, nor is there, in the transverse section of either, any appearance of concentric layers. In neither stem is there any proper pith, the central part of the Sugar-cane being occupied by cells and vessels, and that of the Gourd being alike destitute of both. The cortical texture of the Gourd is represented as composed entirely of cellular tissue; but in it probably are situated the proper vessels, whose place has not yet been accurately noted.

271. In the sections of various herbaceous stems, Other represented by Grew and Malpighi, the number of vessels, and their disposition, exhibit the greatest variety, and approach more or less to the arrangement of parts that is found in shrubs and trees. Thus, in Holly-hock (Alcea), Grew describes the vessels of the bark as yielding a thin mucilage, and within them are the sap-vessels, postured in short rays, which comprise twelve or sixteen vessels. In Scorzonera, the "proper vessels" in the bark yield a milky fluid, and are postured in a radiated manner with the sap and spiral vessels that extend to the pith, all of which form parts of the same radiated lines. (Anat. of Plants, p. 103.) In Endive, Malpighi describes the structure of the stem as approaching in character to that of trees. Near the circumference the vessels, says he, are disposed in lines directed towards the centre, and are separated by small ranges of cellular tissue, which is compressed into a solid and dense form; and more interiorly, the vessels are larger, and extend a considerable way in rays through the stem. (Anat. Plantar. p. 25.) Where the vessels have this radiated position, the cellular tissue between them assumes the form of membranous partitions; but the greater portion of the stem of this plant is occupied by cellular tissue, not thus compressed into a membranous form. We thus clearly observe that, even in herbaceous stems, membranous partitions, extending more or less completely through the stem, are formed, whosoever the vessels are disposed in radii, and are sufficiently numerous to compress, on either side, the cellular tissue that envelopes them.

**Article II.**

*Of the Trunk in Shrubs and Trees.*

Structure of Trunks. 272. In shrubs and trees, the several textures that compose the trunk are commonly distinct from each other; and some parts that are but imperfectly distinguished in herbs, become in them well defined. In the trunks of these plants, however, though a general uniformity of structure is observed, yet particular modifications of it exist in every species, and these are still farther varied by the peculiar nature of the individual plant, and the mode and circumstances of its vegetation. Before descending to particular examples, it may be useful to exhibit a concise view of the parts that compose the trunk, and the terms employed to denote them.

The Skin. 273. Externally in every tree we have the skin or cuticle, the structure of which has been already described in a former section. In very young plants, and in young branches, it is succulent, and its surface is entire; but in older trunks and branches, it is frequently dried and broken, and, in some instances, is thrown off; so that the exterior covering of the plant appears to be formed by the cellular tissue of the cortical texture.

The Bark. 274. Beneath the skin is the bark, constructed, as we have seen, of cellular tissue, and of vessels collected into fasciculi, which at first are strait, and run parallel to each other; but, by the subsequent augmentation of the parts within, are separated at certain places, and touch only at a few points, so as to form a reticulated appearance. In the annual shoot, only a single ring of vessels is observed, and these, with the tissue in which they are placed, form the cortical layer, as it has been called, of that period. Within this layer, a new production of vessels and of cellular tissue takes place, and this being annually repeated, constitutes the series of layers of which the bark is ultimately composed. The new layer that is thus annually formed, and which appears to exercise an active vegetative function, was more particularly distinguished by the appellation of its liber. Liber by the ancients, from its being the substance on which, before the invention of paper, they were accustomed to write. Very frequently, instead of a ring, the vessels of the bark are collected into distinct parcels or clusters, which, in the progress of vegetation, assume very different shapes.

The Wood. 275. Next to the bark is placed the wood, constructed, like the bark, of vessels and cellular tissue. Like it, too, it consists in the young plant, and in the annual shoot of the older one, of a single ring of vessels, which immediately surrounds the pith. In the following year, a new ring of vessels is formed around the first, and in every succeeding year this process is repeated; so that the wood consists at length of a series of rings enclosing each other, and the number of which denotes the age of the tree. The outer ring of newly formed vessels is more succulent than those of older growth, and is generally of a whiter colour; whence it has received the names of sap-wood or albumen. By Du Hamel, and most French writers, it was named ambier, and by Hill it was called the blea. In every annual shoot, the newly formed liber and albumen are in contact; but in every succeeding year they are separated more and more from each other by the interposition of new matter between them; so that at length the first layer of bark, and the first ring of wood, occupy respectively positions the most distant; those, namely, of the centre and circumference of the tree.

276. The vessels that are thus annually formed, and constitute the albumen, are disposed in radii, which extend more or less completely from the circumference to the centre. In some trees, the vessels are much more numerous than in others; and, in the progress of vegetation, they frequently suffer great alterations in size and external figure, as was before observed when treating of the vascular system. In the albumen the size of the vessels is very uniform, and so it continues ever after in some trees; but, in others, it is very various, some being enlarged more than others by a greater influx of sap. With this increase of size, the vessels seem to acquire the spiral character. They are also frequently closed up, in the more aged parts of trees, by the production of vesicles within their cavities; and, in common with the smaller vessels and the cells, they are, in some trees, ultimately filled with gummy or resinous matter. In other instances, where the proper juices of the plant differ but little in quality from the common sap, the vessels, when no longer employed in active vegetation, become dry, and appear, in some plants, like empty capillary tubes, and, in others, from the minuteness of their size, no aperture is visible. In this state, they have been regarded as solid filaments, ligneous fibres, and denominated the ligneous fibres of the plant.

277. From the disposition of the vessels in radii Transverse more or less regular, the cellular tissue, by which Septa they are surrounded, will be more or less compressed in the same direction, and form those transverse partitions between the several rays of vessels, which we have already so frequently noticed. In addition to these fine partitions, described both by Grew and Malpighi, which are thus *interposed* between every ray or line of vessels, larger portions of cellular tissue are observed, at certain distances, which extend in the same direction through the wood, and, in some instances, are continued through the bark also. By the authors just mentioned, these partitions were described as stretching from the bark towards the pith, and were named *insertments* by Grew, and *transverse utricular ranges* by Malpighi. Others have held them to proceed rather from the pith to the bark, and have called them *medullary rays*. We shall venture to name them, in future, *transverse septa*, which name denotes simply their direction, and the fact of their forming partitions between the vessels, without expressing any opinion concerning their origin. For similar reasons, the finer partitions of cellular tissue, previously described, may be denominated the lesser transverse septa.

278. Beside these transverse septa, there are sometimes portions of cellular tissue intercepted between the vessels in a longitudinal direction. This was remarked, both by Grew and Malpighi, in the oak and several other trees: they appear sometimes to be very short, and sometimes to form nearly a continuous ring around the trunk. It is probable they are formed simply by the pressure of the vessels acting in a direction opposite to that by which the transverse septa are produced; they may, for distinction sake, be named the longitudinal septa. In many trees, they are not to be observed, or, if they exist, are so thin as to form only a sort of fascia on the adjacent vessels. To the cellular tissue, promiscuously intermingled with the vessels, some writers give the name of parenchyme of the wood.

279. The only other part of the trunk that remains to be mentioned is the pith. It is situated at the centre, and is surrounded commonly by a ring of vessels, but sometimes, in part, by thickened cellular tissue. Its proportion in shrubs is usually much larger than in trees; and in the young shoots of trees it occupies more space than in the older branches. At first in the young plant it is succulent, but afterwards becomes dry; and in aged trees it frequently is entirely obliterated, or at least rendered solid.

280. In a description of the growth of the trunk in a young plant of chestnut, Malpighi has given clear views of the gradual development of these several parts, and exhibited the appearances successively displayed in the first years of growth. (Anat. Planta, p. 35.) In the Vine, some of these parts are very distinct. Fig. 1. Plate XVII., represents a transverse section of the annual shoot of this plant. The pith (a) in the centre is large, and composed of cells of different sizes. From the pith to the skin in the Vine, and, according to Grew, in the Elm and some other trees, extend the transverse septa (b). In some places, the cellular structure of these septa, in the recent plant is still visible, as at (c); but generally they have the appearance of thickened membranes. Between every two septa, two, or sometimes three lines or rays of sap-vessels are interposed, which, from their size, are readily visible, and their place and disposition are indicated by the dotted marks (d): the circular ring that bounds these vessels seems to be formed of condensed cellular tissue, and exterior to it the proper vessels are placed in the cellular tissue of the bark.

281. In the next figure (fig. 2.) is exhibited the transverse section of an Apple-branch of one year's growth, which, like the former, is considerably magnified. The angulated figure and relative size of the pith at this period are shown: from the pith to the bark proceed numerous very fine septa, possessing somewhat of a curved direction, and between them innumerable black points, indicating the sap-vessels, are seen: these vessels are disposed in radii, and are bounded exteriorly by the thickened tissue of the bark: the bark is proportionally large, and in the midst of its cellular tissue clusters of proper vessels (g) are observed.

282. In a similar section of the Apple-branch of two years growth, fig. 3., more highly magnified, the pith (h) is seen to have assumed a rounder form: from the pith towards the bark the transverse septa extend, between which the vascular radii are situate. The letter i denotes the place of junction of the two years growth; k the newly formed albuminous vessels, situate between the bark and the wood; and l two ranges of "proper vessels," placed in the cellular tissue of the bark. Grew gives a highly magnified view of a section of this same plant about the third year of its growth, in the 25th table of his work, the appearances of which correspond with those just related, except that the transverse septa, as in all his figures, are made to represent strait lines, which, in the earlier periods of vegetable growth, does not appear to be quite correct.

283. Proceeding next to the plant of more mature of the Oak: age, we shall copy from Grew part of a section of the Oak, which in fig. 4. is exhibited on a reduced scale. The letter m denotes the bark; n the albumen; o the wood; and p the pith. In this section, the larger transverse septa (q), and the smaller ones (r), are very distinct, between which the sap-vessels of different sizes, indicated by the dark points, are situate: the letter s points to the proper vessels of the bark, some of which are collected into round parcels, and others form a ring.

284. Beside the transverse septa that intersect the diameter of the tree, we observe, in this figure, other lines (t) placed at right angles to them, and which appear to be interposed between each annual ring of wood. Grew considered it probable that these lines were produced in the Oak, and also in the Fig-tree and Walnut, by a peculiar sort of sap-vessels that existed once in the bark, as did the turpentine vessels distributed through the wood of the Pine. (Anat. of Plants, p. 115.) Hill also calls them sap-vessels, seated on the outer edge of each annual circle, which, in the young plant, contain sometimes a limpid liquor, and, at other times, appear empty. He notices also the existence of proper vessels, containing a thick juice; in the albumen of this tree. (On the Construction of Timber, p. 9.)

285. An examination of this wood at an age still of very old more advanced, may contribute to throw some farther light on its structure. In fig. 5. is given the representation of a transverse section of the central portion of a piece of the wood of very old Oak, of its natural size and appearance. The pith (w) at the centre was completely obstructed, and its cellular character obliterated; the letters x x denote the larger transverse septa, rendered completely solid everywhere, and in some places partially obliterated; and (y) the white lines that extend in the opposite direction, and mark the boundaries of each year's growth. In the substance of these concentric lines, numerous traces of minute apertures were visible, and from one line to another, small irregularly curved lines, as represented in the drawing, were everywhere observed to extend. No vacuity was anywhere perceived to exist, but the whole formed one compact and solid mass.

286. A small and very thin slice of this wood, comprising a part of one of the larger transverse septa, and small portions of two of the concentric lines above mentioned, was submitted to a pretty highly magnifying power, and a delineation of its appearance is given in figure 6. In this figure, the letters \(a'\) denote the two concentric lines; \(b'\) one of the smaller irregular lines that frequently extend from \(a'\) to \(a''\), but are often intercepted, and form irregular spots or patches, as traced in several parts of the drawing; \(c'\), the smaller transverse septa, situated at unequal distances from each other; and \(d'\), the larger septum, the cellular character of which is entirely obliterated. Several small irregular lines, running in the same direction with the larger concentric ones, are also observed; these, at their junctions with the lesser transverse septa, produce a number of little squares, the area of which are filled up with a dotted or punctuated membrane.

287. This microscopical representation seems to confirm the opinion of Grew, that the concentric lines (\(a'\) and \(a''\)) are chiefly composed of vessels: for their apertures, now rendered visible, are of different sizes, and the canal of many of the larger ones is filled up with a vesicular substance, often observed in the vessels of aged plants. The substance that surrounds these vessels appears to be condensed cellular tissue, rendered perfectly solid by the resinous matter with which it is filled. The irregular thickened lines (\(b'\)) that run transversely to the former, are similarly composed of vessels and condensed cellular tissue, and the smaller patches, we have noticed, are made up of the same; both the large and small transverse septa consist of condensed cellular tissue alone, and such, too, appears to be the matter of which the fine lines or longitudinal septa that intersect them are composed. Some observations of Du Hamel, on the formation of the ligneous layers, may aid our inquiries into the nature of these latter septa, and the minute structure of the wood.

288. In a transverse section of the trunk of the Oak, the Elm, or the Fir, says this very intelligent writer, the ligneous layers are distinctly visible, and it is commonly believed that each of these layers is the product of one year's growth. If, however, we cut obliquely a piece of Oak, each layer is then seen, with the aid of a common lens, to be composed of a number of thinner layers, which mutually cover each other. By macerating pieces of wood in water, he was able to separate the annual layers into a great number of leaflets thinner than the finest paper; and these primary layers, as they may be called, he afterwards ascertained, by experiment, to be formed successively during the whole period of active vegetation; so that the layer which is the product of one year's growth, is itself formed of a number of layers exceedingly thin. (Phys. des Arb. Tom. I. p. 31, and Tom. II. p. 19.)

Now, it is probable that, between each of these primary layers, cellular tissue is interposed; and this tissue, by its compression, gives origin to the minute lines which in this tree have been noticed. In several trees, however, no similar lines are visible, because, in all probability, they do not, like the Oak, afford secretions by which the tissue is thickened and rendered apparent. Even in a very thin slice of Oak, when viewed in the microscope by a strongly reflected light, these lines almost entirely vanish, while those of the two orders of proper transverse septa remain.

289. M. Kieser examined the same wood, in the transverse slice of a tree of 100 years of age (Mém. sur l'Organisation, &c. Plate XIV.), and his representation of its structure is copied in figure 22, Plate XVII. In this figure, in which the appearances are magnified 130 times, \(n\) represent the cellular tissue, or, as he calls it, the parenchyme of the wood. At the top and bottom the cells are obstructed, and appear like obscure points (as is the case also in fig. 6, of the same Plate); but in the middle of the figure, the cavities of the cells are said to be still visible: the letters \(o\) denote the apertures of enlarged spiral vessels, all of which were filled with vesicles, but a few only are so represented, as in \(p\); \(q\) indicates the smaller vessels dispersed through the cellular tissue; \(r\) a portion of one of the larger septa, and \(s\) the smaller ones, which are often displaced by the augmentation in the size of the vessels.

290. In this highly magnified representation by Kieser, there is no appearance of the concentric lines or septa which intersect the transverse ones, as noticed by Grew and Malpighi, and exhibited in figures 5. and 6.; but the two orders of transverse septa remain. We before remarked, that, in a slice of wood so very thin, as, when viewed by a strong light, to become translucent, these lines, in a great measure, vanished, and in the figure of M. Kieser, this evanescence is made to extend even to the thickened portion that intercepts the annual layers. It is therefore probable, that all these appearances of concentric or longitudinal septa, are produced simply by the thickening and compression of the cellular tissue in the Oak, and such other trees as have viscid juices, and whose vessels are subject to irregular enlargement; for in whatever position these thickenings occur, numerous vessels are always to be observed. Hence, in very thin slices they entirely vanish, while the proper transverse septa, being formed by the condensation of continuous portions of membrane, remain visible. In these figures, it may also be remarked, that the surface occupied by cellular tissue seems equal nearly to that occupied by vessels; but it is probable that the apertures of many minute vessels dispersed through the tissue, have not been distinguished from the cells. In a highly magnified representation, however, of the wood of this tree by Grew (Anat. of Plante, tab. 3. fig. 7.), the proportion of the vascular to what is deemed the cellular part is still less.

291. The vessels of the bark in the Oak, as delineated by Grew, fig. 4. Plate XVII. are represented as disposed partly in parcels, and partly in a ring; and in all the representations he has given of different trees, the greatest diversity, in regard to the position of these vessels, is found to exist. From the difference in the qualities of their juices, in the texture of the parts, and in the modes and circumstances of their growth, this variation may be expected to occur. In the Oak, the Pine, and many others, it seems certain also, that a part of the cortical texture, or at least vessels containing the proper juices of the plant, are constantly mixed with those of the ligneous texture, and with them contribute to form each an- nual layer of wood. In this respect, therefore, these trees may be said to approximate in structure to Palms, and those trees in which the two textures are uniformly blended, in some of which, the growth is said to take place at the circumference, as in ordinary trees. For examples of the diversity of structure exhibited in the trunk of a great many different trees, we must refer to the beautifully executed plates of Grew.

Section II. Of the Structure of the Branch and its Appendages.

Article I. Of the Branch.

292. From the trunk springs the branch, which, in structure, resembles very exactly that of the trunk itself. Indeed, most of the figures, which represent the structure of the trunk, are taken from sections of the branch; and hence the description of the one serves entirely for that of the other.

293. Branches, in common with leaves, originate from buds, of which we have subsequently to treat, introductory to a description of leaves. At present, we shall describe only the mode of connection between the trunk and the branch.

294. The branch, says Grew, springs not from the surface, but so deep as to take with it not only the bark and the wood, but the pith also, making its way at the parts where the vessels are separated by the transverse septa, and carrying with it the skin, which is extended with it. (Anat. of Plants, p. 28.) The separation of the vessels of the trunk to form the branch is not like the separation of a few filaments from a skein of thread; but they spring, says Du Hamel, from a centre, and bear with them a part of each portion of the tree. Hence if a tree, that is divided into two branches, be cut a foot above the bifurcation, the surface of the sections resembles that of two trunks cut horizontally; if the section be made lower down, at the place where the branches spring, the same appearances of two series of concentric circles are seen at the axis of the trunk, but they are surrounded by other layers common to those which belong to each of the branches; and still lower on the trunk, the concentric circles belonging to each branch diminish, and are finally lost in those which form the trunk from which they sprang. (Phys. des Arbres, Tom. I. p. 93.) These primary branches divide into others, and these again into still smaller branches, which form angles with each other, more or less great, according to the species of tree and other causes.

295. The position of the branches on different trees is very various, but in the same species it is generally uniform. From the measurements of Du Hamel, it appears that, in many trees, the solid matter of the branches that go out from the trunk, exceeds that of the trunk itself in the proportion nearly of five to four. (Phys. des Arbres, Tom. I. p. 96.)

296. Parent and others have supposed that the branches proceeded always from, and were nourished by, the pith; but this opinion has been combated by Du Hamel and Hill. The latter gives a longitudinal section of the trunk of a species of American Dog-wood (copied in fig. 7. Plate XVII.), representing the origin of two buds (f), which are seen in the state of pushing out on either side through the vessels of the wood. In this trunk, the pith is of a brown colour, the inmost ring of vessels green, and the outer ones white. Through the white rings, the inner green vessels are seen to shoot, and the brown pith is left entire behind; though the new branch at length obtains a pith for itself, which, however, has no connection with that of the trunk. In a similar section of an older trunk (fig. 8.), the branches are seen to spring also from the inmost circle of wood; the pith (g) is not at all disturbed, but each branch is furnished with its own pith h. In a section of the Vine, fig. g, a similar origin of the branches, from the inmost circle of wood, is observed; and not only is the pith (i) of the branch distinct from that of the trunk, but the pith of the trunk itself is intercepted by the shooting of a branch (k) across it. (On the Construction of Timbers, p. 35.) This latter fact of the interception of the pith by the shooting of branches across it, was previously noticed by Grew in the Vine and some other plants. (Anat. of Plants, tab. 19.)

297. When a bud thus protrudes to form a branch, the perpendicular vessels of the trunk are compelled to separate, and they afterwards meet above, and pursue their former direction. This is shown in fig. 13. Plate XVII., copied from Du Hamel, in which the bud p', in the act of sprouting, is seen to push to either side the vessels of the trunk, which again meet above it.

298. The vessels, both of the wood and bark, according to the same author, have their direction determined chiefly by the course of the sap. If the sap preserve a perpendicular direction, as in trees that have no branches, the vessels are perpendicular also; but if it move to one side, these vessels then change their direction. This is strikingly evinced in a tree that has been cut over above a branch; for then all the sap being obliged to pass to the young branch, the vessels all at once take the same direction; so that if a tree has been cut over in winter, and at the end of the succeeding spring, its branch below be examined, the new vessels of the branch will be seen to cross those of the trunk, as exhibited in fig. 12. q', Plate XVII. (Phys. des Arbres, Tom. II. p. 53.)

299. In figures 7, 8, and 9, copied from Hill, the young branch, in every instance, is seen to originate from the most inmost ring of vessels that surrounds the pith; and he was of opinion that all buds and branches sprung from this part alone. To this vascular circle he gave the name of corona, and held it to be the most important part of the vegetable body, that it was like no other part of the plant, but contained within itself the essence of them all. (On the Construction of Timbers, p. 21.)

300. It is however notorious, that trees in which not only this first circle, but almost every other circle of vessels has perished, produce leaves and shoots from the trunk where the bark is entire, as this author himself admits, p. 44 of his work. There does not appear, either in the anatomical character, or in the functions of this circle, anything that distinguishes it from the others, except priority of formation, and its being, in consequence, the seat from which the first buds and branches spring.

301. A much more correct idea of the origin of buds and branches was entertained by Du Hamel, who illustrates it by the diagram, fig. 10, Plate XVII. Let us suppose this figure to represent a tree of four years growth, as indicated by the four ligneous cones which, at its base, envelope each other. In the first year, a bud (b) springs from the inmost ring, which, by the fourth year, is seen to consist of four ligneous layers. In the second year, a second bud (a') springs from the ring of that year, and consists only of three layers; the next year, a bud (a'') is developed on the first bud (b), and possesses only two layers; and the bud (c'), developed the fourth year on the outmost ring of wood, is seen to consist only of one layer. (Phys. des Arbres, Tom. II. p. 58.) In this way, every ligneous layer may be considered equally capable of giving origin to buds and branches.

Article II.

Of Thorns.

302. Connected both in origin and in structure with branches are those appendages, frequently observed upon them, called thorns. They are very conspicuous on the hawthorn, and are constituted, says Grew, of the same parts as the bud itself, and in a like proportion. They spring from the outer portion of the ligneous texture, and may be considered as abortive buds. (Anat. of Plants, p. 33.) Malpighi describes them as being frequently produced in the axis of leaves, and to assume for a time the form of a branch; but at length to degenerate into a thorn. He considers them to arise from defective nutrition, and adds, that they disappear frequently under higher culture. (Anat. Planter, p. 138.)

According to Willdenow, most species of our fruit-trees naturally possess thorns, but which disappear entirely and become branches, under higher culture. Even in the Black-thorn, the prickles diminish in number under improved culture, but do not entirely disappear.

303. Sometimes, however, instead of being produced from abortive buds, thorns owe their origin to the degeneration of other organs; the petioles of some pinnate leaves which are persistent become thorns, and the same thing is observed of the peduncles of some flowers. Certain stipulae, also, as those of Mimosa, are said sometimes to change into thorns (Principles of Botany, p. 270); and in the Date, according to M. Decandolle, a lobe of the leaf has been converted into a thorn. (Théorie Élément. de la Botanique, p. 344.) In other instances, as in the Holly, the leaf produces thorns round its entire margin, which are formed by the vessels that bound it. See fig. 11, Plate XVIII.

Structure.

304. When the bark is removed from a branch that possesses thorns, the thorns still remain, by which they are distinguished from prickles that originate from the bark. In fig. 20, Plate XVIII., is a representation of a branch deprived of its bark, in which thorns of different forms are seen to spring from the ligneous texture; and in fig. 21, of the same Plate, is a longitudinal section of another branch covered with its bark, in which the ligneous and cortical textures of the Thorn are displayed. For the descriptions of the varieties of thorns, and their external appearance, we must refer to the writers on botany.

Article III.

Of Claspers and Tendrils.

305. From the similarity in structure which these bodies exhibit to the branches from which they spring, we have placed them as appendages to those members. As is well known, they are met with only in certain plants, and their obvious use is to attach the different parts of the plant to one another, for mutual support, or to the objects in their neighbourhood. In a general manner, they are denominated folcera; the most remarkable species are those which, like the claws of Ivy, called clavicles by Malpighi, are not rolled into a spiral form, and those of the Vine, named tendrils (cirri), which possess a spiral conformation.

306. According to Malpighi, the claws or claspers of Ivy possess a roundish form, and are covered with hairs, which yield a viscous humour, by which they are agglutinated to stones or to walls and trees. Their forms are exhibited in fig. 22, e', f', Plate XVIII., copied from Malpighi; and in the lower part (g') of the same figure, their origin and structure are displayed; they are seen to spring from the ligneous texture of the stem, and to possess a similar structure.

307. The tendril is described by the same author of Tendrils as springing from knots between the origin of leaves. It possesses a round stem, which is sometimes covered with hairs, and this stem frequently divides into several branches. At first it is very tender, but gradually acquires solidity, and assumes the spiral character; its colour is green, and it is composed, like the trunk, of all the common textures. (Anat. Planter, p. 139.) By Willdenow, it is regarded as an abortive leaf, being simply a prolongation of the petiole, without the leafy expansion. (Principles of Botany, p. 272.) Its form, as it occurs in the Vine, is exhibited in the upper portion of fig. 22, h', Plate XVII.; but, in this particular, it is subject to the greatest variation.

308. The leaf itself, as well as the petiole, is said to be sometimes prolonged into a tortuous appendage resembling the tendril; and similar transformations are sometimes exhibited by the peduncle and petals of the flower. In one species of Vine, mentioned by Malpighi, the extremity of the tendril, which is at first pointed, becomes gradually incurvated and reflected, and at length is formed into a roundish body, which is furnished with small papillae, that yield a viscous fluid, by means of which it attaches itself to walls or wood, so strongly as not to be easily separated. In Dodder (cuscuta), small tubercles are formed on the stem, which, according...

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Of Roots. to M. Decandolle, are so organized as to fix themselves on any other plant, and derive nourishment from it. (Théorie Élément. de la Bot. p. 344.) For descriptions of the several varieties of these organs enumerated by botanists, and for the terms employed to express them, we must refer to their works.

SECTION III.

Of the Structure of Roots.

309. Roots possess very different forms, to which botanists have assigned distinct appellations. Some, as those of trees, branch out from one trunk beneath the soil, and are named branched roots; other plants have a number of equally sized roots collected into a bundle, and are called fasciculate, or sometimes fibrous. In other instances, the root is spindle-shaped, fusiform; or shaped like the hand, palmate; or composed of many joints, articulate. In the course of the root, knobs or tubers are sometimes found, giving to such roots the name of tuberous; in others, a fleshy bulb occurs, and such are called bulbous; others run horizontally beneath the soil, and are named creeping; and others are abruptly terminated, or as if bitten off, and called premorse. For examples of these and many other varieties, we must refer to the writers on botany.

310. The root (radix) of the mature plant, is held to consist of two parts; the stock or main body (caudex), and the ramified productions called radicles or rootlets. These parts are generally concealed beneath the soil; but, in the case of parasitic plants, they are inserted into other vegetables. Some of the lower tribes of vegetables have their roots attached to stones, and rocks; and the roots of others have no fixed attachment, but float loosely on water. The different species of Tremella have no root at all; but the functions of this part are performed by the general surface. With regard to duration, some roots speedily decay; others continue permanent. The varieties in their figure have been noticed in the enumeration of their names, and the direction they pursue in their growth, is either horizontal or perpendicular, or in some intermediate position.

311. With respect to structure, the body of the root of trees, says Malpighi (Anat. Plantar. p. 145.), may be regarded as a production and elongation of the trunk beneath the soil; and is constructed of the same textures, disposed nearly in the same manner; therefore it is unnecessary to detail them at any great length. Externally is placed the cuticle, beneath which is the cellular tissue of the bark, with its accompanying cortical layers, the vessels of which have a reticulated form. The bark is thick; its vessels frequently contain the same "proper juices" as those of the trunk, and its cells are alike filled, in some roots, with concreted matter. From the bark to the centre, the two orders of transverse septa are observed to proceed; and are interposed between the rays of vessels, as in the trunk. These vessels, in the root, are often larger than those of the trunk; and instead of a pith, the central part of the root is commonly occupied by vessels. The primary rootlets, which spring from the principal stock, are often tortuous, and are propagated in several successive series, like the branches and ramules of the trunk; from them proceed still finer ramifications (capillamenta), which are the true absorbents of the root, and may be termed capillary rootlets, as they are sometimes named by Du Hamel.

312. In various herbaceous plants, the root has been particularly examined by Grew. (Anat. of Herbs; Plants, Book II.) Its skin is of very different colour and thickness. In the early state, it is represented as an extension of that which covered the radicle of the seed; but in more aged plants, the exterior covering is derived from the cellular tissue of the bark. It is usually, if not always, compounded of vessels and cellular tissue; both of which are distinguishable in many roots.

313. Beneath the skin, the cortical texture is observed, making up, in some herbs, the greater portion of the root, while in trees it is commonly thin. It is composed of cellular tissue and fasciculi of vessels variously dispersed through it, and forming a network, the meshes of which are filled with the tissue. In these vessels, various gummy, resinous, and milky-liquors, similar to those in the bark of the stem, are frequently contained; and it is by their presence that the position of the vessels is best distinguished. Very frequently they make a ring at the inner edge of the bark, "in which place and position," says Grew, "they stand in most, if not all roots, how variouslysoever they are posited also otherwise." They occur, however, in clusters in the bark of many roots, and in others are disposed in rays, or seen sometimes to be irregularly dispersed through the cellular tissue in common with the sap-vessels. The cells of this tissue sometimes preserve nearly an uniform size; in other instances they are of very irregular forms; and frequently are compressed into transverse septa, which everywhere intercept the vessels, and are of very various size and number; they are the receptacles of liquor, but are often found empty.

314. The woody part in herbaceous roots is described as consisting of vessels and cellular tissue; this tissue forms sometimes transverse septa, but in some roots it is disposed in rings. The vessels are disposed either in separate fasciculi, or in rays, or rings. In number and size they vary much in different roots, and also in the same root; they generally appear empty, but may sometimes contain sap; they frequently occupy the centre of the root to the exclusion of pith; but near the top of the root, a pith is often to be found.

315. Having given this general description of the structure of roots, we shall now exhibit a few examples of it. In the young state of the herb, this structure has been already displayed in sections of the pea and gourd, figures 12, 13, and 17, Plate XVI. In the root of the Gourd, at a later period, M. Kieser delineates four large fasciculi of vessels, each of which contains between thirty and forty vessels; the larger vessels are situated near to the circumference, and the smaller ones towards the centre of the root; they all exhibit the spiral character, and many of them are obstructed by vesicles. (Mém. sur l'Organisation des Plantes, Planche X.)

316. In fig. 13, Plate XVII., is a transverse sec-

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Of Roots of Asparagus, copied from Grew, but on too small a scale to show more than the relative position of the parts; the letter r denotes the bark, at the inner margin of which the proper vessels are placed in a ring; s', the sap-vessels or woody part placed more interiorly; and t', the pith at the centre. A very highly magnified representation of this root is given by Grew in table 10. of his work. If his view of its structure be correct, it exhibits a remarkable difference in the arrangement of parts in the stem and root; for the stem of Asparagus is one of those in which neither distinct bark, nor wood, nor pith, exists; but the cortical and ligneous textures are blended together.

317. In the root of Mallow, the position of the vessels is quite different, as exhibited in fig 14., in which the letter v denotes clusters of proper vessels, postured in a radiated form in the cellular tissue of the bark; within these rays is a portion of cellular tissue, through which a few sap-vessels are dispersed; but they are chiefly accumulated at the centre (w) of the stem. In several of Grew's tables, transverse sections of various other herbs are given, which display the greatest possible variety, in the proportion and arrangement of the vascular systems of the bark and wood; to them we must refer the reader who may desire farther information.

318. In shrubs, the arrangement of the parts of the root is commonly more distinct than in herbs, and corresponds with that in the trunk. In the transverse section of the root of the Vine, fig. 15. the letter x' denotes the place of the "proper vessels," situated in the cellular tissue of the bark; y', the sap-vessels extending in radii to the centre of the root, which is altogether destitute of pith; and z' marks the transverse septa which are interposed between the rays of vessels. Of this figure a very highly magnified view is also given by Grew in table 17. of his work. In table 16. the same author represents the structure of the root of Wormwood. His delineation of it is copied in Plate CCCCXX. (Article Plant) in the body of this work, to which we refer the reader. The disposition of the parts resembles almost exactly that of the Vine, except that the "proper," or "balsam vessels," as he calls them, are placed at greater distances from each other; and, from containing a viscid fluid, are enlarged, and rendered more distinct.

319. We before noticed the manner in which the rootlets were given off from the radicle in the Pea and the Gourd. All parts of the root possess the power of emitting rootlets when they are placed in favourable circumstances; and this power is possessed also by the branch. If the branch of many trees be cut off and planted in the earth, it emits rootlets from its sides beneath the soil, and becomes at length an entire plant, possessing the several members of root, trunk, and branches. If even the bark of a branch be partially removed, so as to intercept the course of the descending sap, and the detached part be, at the same time, surrounded with moist earth in the manner of a graft, the upper portion of the divided bark will emit rootlets into the earth; and if, after a certain period, the branch be separated and planted, it will form a tree, sooner, it is said, than by most other methods. The simple immersion of the cutting of some trees in water, as of the Willow, is sufficient to elicit the production of rootlets. The origin of these has been traced by Malpighi in the Will. (Anat. Plantaar. p. 146.), and is exhibited in fig. 16. low.

Plate XVII.; in which is represented a longitudinal section of the cutting of the willow, and of the rootlets it emits from its sides. These rootlets spring from the cutting, just at the surface of the water, not below it. They appear, at first, like small tumours in the bark, which protrude and gradually force their way through it, forming fissures, which are, as it were, bordered by a lip, and afford passage to the springing rootlets. In the figure just referred to, a denotes the outer portion of the bark that forms the lip; b, the inner portion which protects the springing rootlet; ccc, three rootlets which are seen to originate from the perpendicular vessels of the wood.

320. The capillary rootlets which thus spring from the larger roots, and from branches, are much more rootlets, simple in structure than buds, being made up chiefly of the ligneous texture of the trunk, which, in shooting, carries with it a portion of the cortical texture that covers it. They are the organs which absorb nutriment from the earth, and convey it into the larger rootlets, by which it is transmitted to the trunk. Hence, as Du Hamel observed, the earth is exhausted of its nutrient matter, chiefly where these capillary rootlets are distributed, and not in the neighbourhood of the larger roots. On examining the roots of trees, after a severe winter, he found these capillary rootlets to be generally dead, which led him to suspect that trees lose, in the earth, their annual rootlets; as, in the air, they lose their leaves. He found, that, even after slight frosts, during every period of winter, many of these capillary rootlets were destroyed; and that, when the temperature became milder, new rootlets were developed, which abundantly replaced the others. (Phys. des Arbres, Tom. I. p. 88, 89.)

321. Analogous to the production of rootlets from the branches, when the descending sap is intercepted, is that of the emanation of similar organs from the knots in the stems of many plants, as those of the Gramineae. Wherever a knot of this description is brought into contact with the moist earth, numerous rootlets break out, and buds also, from which entire plants are produced. In the culture of the Sugar-cane, the propagation of the plant is continued entirely in this way, and never by means of seed; in the several modes of engrafting, and various other horticultural operations, the cultivation of vegetables proceeds on a similar principle; for the graft, which is attached to and becomes rooted in another tree, may, by a different method, be made, like the cuttings of willow, to furnish roots from its own substance.

322. In some plants, as filipendula, the roots and Tubers rootlets swell out into globular bodies, or tubers of the shape of olives: these tubers are composed of vessels with a large portion of cellular tissue, and from them other rootlets spring. In other instances, the tuber that forms on the root is a true bud, which acquires a large size, and from it the real rootlets, possessing a filiform figure, also spring. (Malpighi, Anat. Plantar. p. 150.) The bulbs attached to the roots of many plants are likewise to be regarded as real buds, and will be briefly noticed in the next section.

323. M. Du Hamel has made many observations and experiments on the effects of the soil in determining the form of the root. All roots that spring from seeds have, according to him, a spindle shape, if they are made to grow in soil that is easily penetrable. He has seen the root of a young Oak extend in such a soil to the depth of four feet in the form of a tap-root, when the stem possessed only six inches in height. If, however, at a small distance from the surface, it meet with obstacles, which oppose its descent, it then continues short, and divides into lateral branches. A similar production of lateral branches is observed, if, by any accident, the leading trunks of the root be destroyed.

If, on the contrary, a trench be dug in the neighbourhood of a root, and then filled up with fresh earth, the root will extend through the soft earth, without producing lateral branches; and the same often is observed to occur in very moist situations. The direction of roots is also greatly varied by the qualities of the soil, for they extend into that which is richest, while the barren parts are nearly destitute of roots. (Phys. des Arbres, Tom. I. p. 82.) So great, indeed, appears to be the influence which the qualities and texture of the soil exert on the growth of roots, that in many instances, before we could pronounce on the true form of a root, it would be necessary to define the kind and condition of soil that is most natural to it.

CHAP. III.

THE ANATOMY OF THE ORGANS OF VEGETABLES.

SECTION I.

Of the Structure of Buds.

324. In the preceding chapter we have described the larger and more permanent members of the plant, which produce and sustain all the other organs: we have now to delineate the form and structure of these organs, which have a more temporary existence, and present a more diversified character. They may all be said, either directly or indirectly, to originate from buds, with which therefore we shall commence our descriptions.

325. A bud, according to Gärtner, is an organic body, sprouting from the surface of a plant. In the beginning, it is distinct from the proper and permanent members of the plant, but after some time becomes a part of it; or, if separated, is capable, by the increase of its own proper substance, of growing into a new plant, perfectly similar to its parent. (De Fructibus Plantar. p. 3.)

326. Buds may, in general, be easily distinguished from seeds; but in some of the lower tribes of vegetables, the conformity in external appearance and internal structure is said to be so great, as to render this a matter of much difficulty. This appears to arise principally from the extreme minuteness of the organs of reproduction in those plants, and the consequent uncertainty in discriminating their true character; so that botanists are not agreed as to what, properly speaking, should be termed a bud, or what may be deemed a seed; some choosing to regard as a bulb or bud what others denominate a seed.

327. Gärtner enumerates four species of buds, two of which are leafless, and two are provided with leaves or scales. The first, propago, is the most simple species of bud; it is leafless, and possesses different forms; sometimes it is entirely naked, and sometimes is enclosed in a bark-like case; it at length separates spontaneously from its parent, and is dispersed like a seed.

328. The second species is termed gongylus: it is described as a perfectly simple, leafless, somewhat globular and solid bud, concealed within the bark of the parent plant, and never separating spontaneously, till the bark decays by age. It has a great affinity to the tuber of roots, but differs from it in not being a proper member of the plant, and in not possessing the principle of multiplication which resides in the tuber.

329. The third species of bud is a compound germ, and named bulbus. Its figure is somewhat globular; it is nearly leafless, and formed of a very short keel (carina) and thick succulent scales, and at length separates spontaneously from its parent. Of this species there are two varieties, the one solid, constructed of a solid fleshy body, and having generally the rudiments of the new plant fixed outwardly upon it; the other coated, being formed of several concentric scales, in the centre of which the young plant is cherished.

330. The last species of bud, and that which is strictly so named, he denominates gemma. This is a bud composed of a subulate keel, and distinct herbaceous leaflets; it resembles a branch in miniature, and never separates spontaneously from its parent. It is named an eye (oculus) when it puts forth flowers alone, or flowers and leaves together; and simply a gem (gemma) when it is unfolded into leaves alone.

331. Of these several species, the last, gemma, is generally considered as alone entitled to the appellation of a true-bud, by those who consider scales and leaves as essential to its constitution; but this definition, says Gärtner, would exclude even bulbs, and it is better to derive our idea of a bud from a general agreement in properties, and particularly from similarity of origin in formation and evolution, than from the ever-varying condition of external form. The two former species of buds occur in the lower tribes of vegetables; the two latter are observed on the stems and branches, and roots of various plants. On the present occasion, we shall notice the latter only.

332. That variety of bud which is called a bulb, and which springs from, or is variously attached to, the roots of many plants, has already been stated to exhibit considerable difference in structure. It is sometimes constructed of several thick scales or leaves enveloping each other, and is sometimes formed of a more continuous and solid substance. To the first description belongs the bulbous substance of the lily and tulip. Grew has given a section of the lat-

VEGETABLE.

Of Buds. ter, made in the month of September. It displays the tunicated structure of the bulb, at the base and in the centre of which, the young flower, destined to appear in the following spring, is observed. See his Anatomy of Plants, tab. 63., or Plate CCCXXI. fig. 17., in the body of this work, accompanying the article PLANT. Of the tunicated variety, the common onion affords also a good example. The coats that compose its bulb, are to be regarded as fleshy leaves, and the true root, according to Du Hamel, is the fleshy plate that supports the bulb, from which the rootlets spring. The common potatoe affords an example of the solid bulb, on whose surface numerous buds, all capable of producing entire plants, are seen. Botanists enumerate a great many other varieties of bulbs, for which we must refer to their writings; and to the works of Malpighi and Du Hamel for the anatomy of many of them.

333. The true bud of the stem and branch was distinguished by the ancients into two kinds, according as it produced either a leaf or a flower, and to it they assigned different names. "Germen autem est id quod ex ipsis arborum succulis primo vere exit, ex quo deinde folium producitur," says Pliny: and this he distinguishes from the flower-bud, "nam gemma proprie floris est." By Grew, the term germin, and by Malpighi, the word gemma, is employed to denote each variety of bud. By Linnæus, the term germin is used to denote, not the bud of a branch, but the rudiment of a seed; and not the rudiment of the seed only, but the organ also that contains it. The word gemma he uses to denote a bud. Gaertner adopts the word germin in a generic sense, to express every species of bud, and with Malpighi and Linnæus, employs the term gemma as indicative of that species now under consideration. This, therefore, as the most generally received appellation, we shall in future employ.

334. During summer, says Du Hamel, buds are gradually formed in the axils of the leaves, viz. in the angle which the petiole forms with the branch. They are at first exceedingly minute; are seen in winter chiefly on the young branches, sometimes on the larger ones; and more rarely on the trunk. They exhibit different forms, according to the kind of tree that bears them, and are attached to it by a very short pedicle. Their position on the branch was considered by M. Bonnet to be reducible to five classes; sometimes they are situated on opposite sides of the branch, but placed alternately, and sometimes they are placed exactly opposite to each other. In other instances, they form a kind of ring round the branch. Sometimes they have a spiral disposition; and at others constitute a sort of double spiral around the branch. In those cases, where the buds stand opposite on the branch, the extremity of the branch is frequently terminated by three buds; but where the buds are only alternate, the young branch is commonly terminated by a single bud. In the Pine, the true buds are placed, not in the axils of the leaves, but at the extremity of the branch alone. Some buds stand out a considerable distance from the branch; others are placed in close contact with it; and these varieties occur sometimes on the same branch in regard to the buds that issue from its sides and extremity. The shape of buds is also very various—some being long and pointed, others short and round; some again are hairy, others smooth; some very small, and others large. (Phys. des Arbres, Tom. I. p. 99.)

335. Beside these varieties in position and form, Leaf and which serve to distinguish the buds of different genera and species, there are also many sorts of buds to be observed on the same tree, whose characters are discoverable by their form. Those which are pointed, usually produce leaves and branches; and from those which are large and rounder, commonly proceed flowers. The former are named leaf or wood buds (gemmae foliiferae); the latter flower or fruit buds (gemmae floriferae); others, which possess both leaves and flowers, have been called mixed buds (gemmae mixtae.) In some trees, as those of Apple and Pear, two varieties of wood-buds occur, one of which is small, produces only a small bunch of leaves, and in the end becomes a fruit-bud; the other is larger, and gives origin to a branch.

336. As the rudiments of the flower appear in the formation of roots, the season before they are destined to bloom, so those of the leaf and the flower are distinguishable, at the same period, in the bud of the branch. They are to be perceived, says Du Hamel, in autumn, and continue to grow even during winter, appearing to be clandestinely formed in that season, when the movements of the sap seem to be suspended; and are thus prepared to shoot forth on the return of spring. It is, however, only in perennial plants that these phenomena are observed. Annual plants do not produce buds, and even those whose roots survive the fall of the stem, produce buds only on their roots. (Phys. des Arbres, Tom I. p. 103.)

337. Climate appears to exert the greatest influence on the formation and evolution of buds. In cold regions, as we have just observed, the bud is formed many months before it is destined to shoot into a leaf or branch; but in warmer regions, scarcely any interval occurs between the periods of formation and evolution. The buds in such climates, are said to unfold themselves immediately from the bark into branches, without having remained, in the form of buds, for any length of time. Sometimes, in the milder seasons of our own climate, the evolution of buds rapidly succeeds to their formation, and the vegetative process with us, emulates the productive powers of more favoured climes. In some examples, however, the specific characters of particular plants overcome these general tendencies of climate; and thus hot climates are said to possess some bud-bearing plants, and in colder climates, there are a few shrubs which are said never to bud. (Willdenow's Princip. Botany, p. 273.) It seems, however, more correct, to consider all plants as bearing buds, from which the branches, the leaves, and the flowers, successively proceed; and to say that in warm climates in general, no suspension of the vegetative process occurs as in cold ones; and no marked interval is observed therefore between the formation and evolution of buds. The few exceptions that occur respectively in warm and cold climates, must be considered in reference to the specific characters of the individual plants. The process by which buds are actually formed, has been called Gemmation or Gem-

mification.

338. Having made these few general remarks on the nature and formation of buds, we have next to exhibit a few examples of their structure and evolution, confining ourselves at present to a description of those which produce either branches or leaves. The mature bud consists of two parts—one that forms the new branch or leaf, and in the language of botanists may be termed persistent—the other serving only a temporary purpose, and falling when that purpose is accomplished. To the former may properly be applied the term germ or gem, and the latter, from its office, may be called hybernaculum. In its leading characters, the bud bears a near analogy to the more perfect seed; for the germ very exactly resembles the plume; and the hybernaculum, as we shall see, in structure, office, and duration, approaches near to certain cotyledons.

339. The leaves or scales which constitute the hybernaculum, and which, in future, we shall denominate the hybernacular leaves, vary much in number, size, and figure, in different buds. Even in the same bud, the inner ones are thinner, and much more tender and succulent than the outer, and are besmeared with a viscid humour which intimately unites them; while the outer ones are commonly hard, hairy, and of a scaly texture. Like the cotyledonous leaves of seeds, those of the hybernacle sometimes grow for a certain time with the germ, and fall successively, at periods more or less distant; they are also not less distinct in figure from those of the germ, than the leaves of the cotyledon are from those of the plume. This arises from the peculiarity in the distribution of their vessels, which do not spring from one common central trunk, as in ordinary leaves, but are derived from several distinct fasciculi at the base, like those of the cotyledonous leaf, as seen in that of the Gourd, Plate XVI. fig. 11. According to the manner in which they are disposed or folded up in the bud, botanists have assigned them different names, for an account of which we must refer to their writings. In the opinion of Du Hamel, they all derive their origin from the inner layer of the bark, of which they seem to be only a prolongation. (Phys. des Arb. Tom. I. p. 103.)

340. The germ of the bud, which is contained within and protected by these enveloping leaves, is composed of one or more leaves generally folded and curled; but in some instances open and expanded. At first they are very small, and their form is indistinct, so that the pedicle alone is distinctly visible, from which branch off the vessels that form the middle rib, and are afterwards expanded to construct the lobes of the leaf. From the figure, which the germ possesses before its expansion, being like that of a keel, its vascular portion, at this period, has been named carina, and its softer part medulla or pith.

341. With respect to the particular portion of the branch, from which the germ internally derives its origin, opinions have much varied. Some have held that it proceeded from the pith alone; others from the first circle of vessels that immediately surrounds the pith; others from the tender wood alone; and others from the pith, the wood, and the bark conjointly. Grew held this latter opinion. (Anat. of Plants, p. 28.) Malpighi describes the germ as a tender ligneous substance, formed of vessels and cellular tissue, and surrounded by its proper cortical texture. (Anat. Plantar. p. 45.) According to Du Hamel, it originates from the ligneous texture and the pith (Phys. des Arbres, Tom. I. p. 103.); and Hill considered it to spring from the first circle of vessels alone, but not to carry with it any portion of the pith.

342. As every germ is composed of the cortical and ligneous textures, it may be said to originate in part from both, as all these writers seem to admit. Sometimes also the pith of the germ is continuous with that of the branch; but, in other instances, no such connection subsists, and there is nothing in the character of the pith of the trunk that renders it at all essential to the constitution of the germ. That, in many instances also, the germ springs from the first circle of vessels, is most certain; but it is not less certain that buds spring from trees long after this first circle of vessels has lost its vegetative power, or has been entirely destroyed. The view already given of the origin of rootlets from a branch, fig. 16. Plate XVII. seems very nearly to represent that of a bud, the latter possessing only a larger portion of cellular tissue in the composition of its bark and pith.

343. In the oak, Malpighi describes the entire bud as consisting of many scales enveloping each other, Oak. and forming an oval body. When evolution commences, these open and expand, and in part fall; but two generally remain and protect the springing germ for a long time. In fig. 17. Plate XVII. is represented one of the hybernacular leaves (d) of the Oak-bud, at the base of which the germ (e) is placed. The leaf (d) is described as possessing an oblong form, and is very evidently vascular; the germ is exceedingly small, and is represented as possessing at this period only one fasciculus of vessels. By degrees, three fasciculi become apparent, which are continued through the germ, and form three pointed extremities, as in fig. 18. A. These parts augment, and the vascular fasciculi separate, so as to produce successively the appearance in fig. 18. B. and in fig. 19. (f.) At length, the small curled leaf (i) rising between the two hybernacular leaves hh, fig. 20. is seen to resemble the plume of the seed, and to possess a form altogether different from the enveloping leaves, which, in appearance, resemble more the cotyledonous leaves of certain seeds. In fig. 21. is given a vertical section of the germ considerably magnified, in which k denotes the pith that occupies the centre of its pedicle; it is enclosed by vascular fasciculi (l) that send off through the bark (m) ramifications to the several little processes that compose the serrated border of the leaf. (Anat. Plantar. p. 41. 45.)

344. But the method of nature, in the evolution of buds, continues Malpighi, is not always the same; for the hybernacular leaves do not always waste and fall as those of the germ increase. On the contrary, in many trees, these leaves, especially those about the base of the bud, losing their primary figure,

VEGETABLE.

Examples of this sort occur in Laurel, in the Apple, the Almond-tree, and many others. In other instances, as in the Rose, the permanent leaves seem to be generated out of those of the hybernaculum, from the apex of which they emerge; and gradually the latter is changed into a sort of petiole, to the sides of which two slender appendages, the remains of the former hybernacular leaf, adhere. (Ibid. p. 41.) Similar transformations are said to occur in many other plants.

345. The buds, such as they have been described, pullulate variously from the sides of stems and branches, and always above the insertion of the fallen leaves; but they spring also from their extremities, and produce the annual elongation of the branch or stem. The manner in which this takes place, and the appearance which the parts exhibit, have been well illustrated by the observations and dissections of M. Du Hamel. In the evolution of the seed, the plume, as we have seen, rises above the earth, and produces the stem which puts forth leaves. When these leaves fall in autumn, the stem continues, and is terminated by one or more buds. The roots, as already remarked (238.), do not increase in length, but at their extremity, and therefore never elongate, after the smallest portion of their extremity has been cut off. It is not the same with branches; for the newly formed part of the young shoot actually elongates, especially at its extremity, where it is most succulent and tender; less in the parts lower down where it is harder; and in its more ligneous parts not at all—as Du Hamel, by very simple and decisive experiments, ascertained. (Phys. des Arbres, Tom. II. p. 14.)

346. The appearance, structure, and evolution of a bud, at the extremity of a branch of the Horse-chesnut-tree, are given by the same ingenious author, whose candour, ability, and success in the prosecution of these curious researches, render him worthy to rank by the side of Malpighi and Grew. In fig. 1. Plate XVIII. is represented part of the annual shoot of this tree, terminated by its appropriate bud, formed in autumn, and which is the commencement of the next year's shoot. In fig. 2. a vertical section of the same bud is exhibited, in which the number and disposition of the hybernacular leaves that envelope and protect the germ in the centre are displayed. In the stem of the shoot, the letter a denotes the pith, which is surrounded by the wood bb, and this again is covered by the bark cc. In fig. 3. is represented a section of part of the bud, detached from the woody part of the shoot, and a little magnified, to show that the leaves of the hybernaculum take their origin from the inner portion of the bark.

347. Proceeding next to the interior part of the bud, Du Hamel represents it as composed of numerous small leaves (fig. 4.), which are more and more minute as we proceed inward, and are covered with fine hairs. In fig. 5. is a branch-bud of the Peach, as seen in February, after all the enveloping scales have been removed. It is composed of greenish filaments, ranged nearly as they appear in the figure.

When some of these filaments were detached, and viewed with the microscope, they appeared toothed at the edges, as in fig. 6., and were covered with hairs. All these filaments were afterwards detached, in order to disclose a small body lodged within them, and which appeared to consist of two small leaflets, folded and toothed at their edges, but not covered with hairs. It is represented in fig. 7. It occupied the centre of the shoot, and seemed to be connected with the pith.

348. In the next figure 8. is represented the bud of the Horse-chesnut, in the state of evolution. The letters dd indicate the scales of the hybernaculum thrust aside by the shooting of the germ e, accompanied by two permanent leaves ff. The letter g denotes the place of a second bud. A vertical section of the same bud is shown in fig. 9., from which all the scaly envelopes have been removed. It exhibits an entire shoot of one year's growth, attached to part of one of two years. From h to i denotes the growth of two years; and from i to k that of one year, with the germ k in the centre and the lateral leaves, as in the preceding figure. The letter l marks the pith, mm the wood, and nn the bark of the young branch. From l to n, the pith is white; from n to o, greenish; and towards i, it is of a brownish red colour. From i to k, which marks the extent of the annual shoot, the pith is green and succulent; and at pp, it is seen to be prolonged into the lateral branches. The wood of two years' growth, from m to i, is white, and forms a continuous tube round the pith, except where the branches go off. It is covered by another layer so thin as to be scarcely visible, but which will, in the end, become wood; and this layer is covered by the bark. The ligneous layer of the annual shoot appears to be a prolongation of the new layer of the older one, and, like it, possesses at first an herbaceous character. The cortical layer also seems to be a prolongation of that of the older shoot. As to the pith, though in both shoots it is continuous, it is to be observed, that that of the older branch is white and dry, and that of the young shoot green and succulent. (Phys. des Arbres, Tom. I. p. 117.)

349. It is thus by the formation of a bud in autumn at the extremity of a branch, and the shooting of branches and growth of that bud in the succeeding spring and summer, that the trunk of the tree and its branches are annually elongated. During the first season, the shoot retains, in great part, its herbaceous characters; but, in the second, it becomes perfectly ligneous. In the axils of the permanent leaves of the young shoot, the rudiments of new buds become apparent, even in the first season.

350. It was before remarked, that trees receive an additional circular layer every year, and that from these new layers buds successively spring, so that the earliest branches may contain as many ligneous layers as the trunk, and those of later formation a smaller number, according to the year in which they shot forth, and the circle of wood from which they sprang. Combining this growth in breadth with that in length, it will appear, says Du Hamel, that at the base and centre of a tree 100 years old, there is wood of 100 years of age; whilst, at the exterior part of the same tree, and at the extremities of its branches, there is wood of one year's age only. As the latitudinal growth was before illustrated by a diagram, a similar mode may be adopted to explain the longitudinal increase.

351. Let figure 10. Plate XVIII. represent in \( q r \) the ligneous portion of a tree that has proceeded from a seed in spring, and is observed in autumn. The following spring, a second shoot proceeds from the bud \( r \), which reaches as far as \( s \); but, at the same time, there is a second ligneous layer formed on the first shoot \( q r \), by which its thickness is proportionally augmented; and, at the end of the second year, the tree has the form and extent of the unshaded portion of the figure \( q s \). The next spring, the bud (\( s \)) opens and sends out another shoot to \( t \); and ligneous layers are added as before to the two preceding shoots; and thus the tree is extended from \( q \) to \( t \). The fourth year the same processes are repeated, and the tree extends from \( q \) to \( w \); and each annual shoot, from the base to the summit of the figure, is seen to be composed successively of four, three, two, and last of one layer in thickness. This figure, therefore, illustrates the mode in which trees increase at the same time in height and breadth. The ligneous layers may be compared to a series of cones which envelope each other, and which annually augment the diameter of the tree by the two thicknesses of the layers. It shows also that trees grow much more in height than in breadth, and that this growth is effected by the successive formation and evolution of buds at the extremity of the stem, precisely as the first shoot issues from the seed. (Phys. des Arbres, Tom. II. p. 50.)

Section II.

Of the Structure of Leaves.

352. These are organs of great importance in the vegetable economy; they are not, however, universal, for the Cactus, some species of Schemus, and a few other plants, are considered to be destitute of leaves. Like other parts of the plant, they may be regarded with reference either to their external form, or their internal structure. The former view belongs more especially to the botanist, who has very happily applied his descriptive language to portray the almost infinite diversity of figure, size, and character, which the leaves of different species of vegetables exhibit. On this branch of the subject we shall but lightly touch, recalling simply to notice the more leading distinctions of the botanist, and such only of them as may appear to be more immediately connected with the structure of these organs.

353. The leaves (folia) are distinguished and denominated according as they are simple or compound. Simple leaves are such as have only a single leaf on the stalk or petiole that supports them, and where all the parts of the leaf are continuous with one another. Compound leaves are those which are made up of more than one piece, or where the leaf is formed of parts or leaflets articulated together. In regard to their place, situation, and insertion, leaves are said to be determinate. By the place of a leaf, is meant the part of the plant to which it is attached. By situation, is understood the disposition of the leaves on the stem or branch, which corresponds to that of the buds. By insertion, is expressed the mode of connection between the leaf and the stem or branch; and the direction of leaves is considered to bear reference to the position in which they stand to the stem.

354. The foregoing observations apply to leaves considered in connection with other members; when we regard them singly, we remark several parts which are common to almost all leaves, and to which particular names have been assigned. The part at which the leaf springs from the branch or stem, whether directly or by means of a petiole, is called the base, and the point opposed to this, the apex of the leaf. Each leaf has also two sides, faces or surfaces, as they are indifferently called. The prominent lines that appear on these surfaces were named riblets (costulae) by Malpighi, and have very improperly been called nerves by most writers; for the term nerve denotes an organ of a totally different nature, of which not even the existence has yet been demonstrated in any part of the vegetable system. To the line that circumscribes and forms the boundary of the leaf, the term margin is commonly applied.

355. The figure of leaves exhibits the greatest diversity, to express which various terms are employed; their margin also is either entire or variously fissured, notched, or toothed; their surfaces are naked and smooth, or clothed with hairs, and studded with excrescences; sometimes they are plain and flat, at others furrowed or plaited; and in all these particulars, the opposite surfaces present also the greatest diversity. In size, leaves exhibit the most remarkable differences; and, with respect to substance, some are exceedingly thin, and have a membranous texture, others very thick, and of a fleshy nature. As to colour, they exhibit every shade of green, from the most gay and lively, to the deepest and most obscure. In some, the tint of colour approaches to blue; in others to red; and previous to their fall, they all undergo those changes of colour which produce the diversified beauties of an autumnal scene. The period, however, at which this occurs, is very different. Some leaves fall early, before the summer has passed, and are termed caducous; others retain their place till autumn, and then fall, and are named deciduous; others continue beyond the summer, and are styled persistent; and others, which have a still longer duration, are denominated perennial.

356. In the preceding section on the structure of buds, we exhibited the form and appearance of leaves in the earlier periods of their existence. They were shown to possess a very minute size, and to be curiously folded up, and concealed within their various scales or coverings, which effectually protected them from the rigour of the winter season. The germ of the bud, from which the leaves originate, was stated to be composed of the same elementary parts as the stem and branch from which it sprang. From the ligneous ring in the annual shoot, it derived its vessels, which, after having traversed obliquely the cortical layers, were prolonged into the pedicle by which it remained attached to the branch. This pedicle Of Leaves was shown to consist of a pith, encircled by vessels, which branched off through the cortical texture, to form the keel of the germ in its folded state; and, in its more expanded forms, to constitute the vascular riblets of the leaf. By subsequent growth, this gradually extends and elongates, becomes more ligneous, and is formed, at length, into the slender stalk or petiole, by which the leaf remains attached to the branch. (Phys. des Arbres, Tom. I. p. 123.)

Structure of the Petiole

357. The vessels, which are given off from the branch to form the petiole, are not collected into one bundle, but constitute several fasciculi, which are disposed, in different ways, about the centre of the stalk. In some stalks there are three, in others five or six, and in others seven or more fasciculi, all placed, says Grew, either in an angular or circular posture, and at a greater or less distance from the centre. This centre is generally occupied by a pith, but sometimes it is hollow or tubular. In table 49. of the Anatomy of Plants, several transverse sections of the petioles of the leaves of different plants are given, exhibiting the different modes in which these fasciculi are dispersed through the cellular tissue that forms the greater portion of the stalk. In every instance, the pith and bark of these petioles are represented as forming one continuous substance. In some plants, the fasciculi of vessels that come off from the stem are not collected into a cylindrical figure, but, after being variously implicated with each other, expand at once into a leaf. Such leaves rise by a broad base, and, from being destitute of a petiole, are termed sessile, forming often a sort of sheath about the stem, of which several varieties are enumerated by botanists.

358. The petiole, as it springs from the branch, may be compared to a small stem, which, at the basis of the leaf, expands into numerous branches. Frequently, it is continued through the centre of the leaf, forming its middle rib, and giving off, in its course, numerous branches. At other times, on reaching the base of the leaf, it separates at once into three or more equal portions, which form as many distinct leaves or parts of a leaf, supported by their respective petioles. The structure of the petiole is the same as that of the branch, being composed of the ligneous and cortical textures, in which sap and proper vessels are discoverable, and the whole is invested by the cuticle.

359. Where the petiole terminates, the proper or expanded portion of the leaf commences, the figure of which is determined by the number and distribution of the vessels. These vessels divide and ramify in various modes, till at their termination they form a finely reticulated structure. In many recent leaves this structure is very visible, but when the softer parts are removed by spontaneous decomposition, the vascular system of the leaf remains nearly entire, and its extent and form are then more completely exposed. In fig. 11. Plate XVIII. this distribution of the vessels is exhibited in a leaf of Holly. From the central fasciculus, branches are everywhere given off, which farther subdivide, and form smaller ramifications, that terminate, at length, in a minutely reticulated structure. Around the margin of the leaf, the vessels are continued, and, at certain parts, are prolonged into the thorns that bound the circumference of this leaf.

360. In this, and similar instances, the vessels appear to be ramified out of greater into less; but, as already observed (sect. 9.), this does not appear to be really the fact, the vessels being all of the same size everywhere in the leaf, and all continued through it, like so many distinct tubes. This structure Grew represents in a highly magnified view of the leaf of Borage, in table 50. of his work; part of which is represented, on a reduced scale, in fig. 13. Plate XVIII., designed to show that the ramified vessels (o) are all clusters of tubes of the same size, which, though they separate continually, and come into contact, are never produced, or ramified one out of another. Neither do they ever inoculate or anastomose with each other, until, according to Grew, they come to their final distribution.

361. The vessels thus distributed through the leaf belong chiefly to the order of spiral vessels, as was shown by Grew in the leaf of the Vine, and many others; and, from the observations of Malpighi, Darwin, and Knight, already related (sect. 57.), it appears, that "proper vessels" are everywhere associated with them. It would seem, from the observations of Darwin, that these two orders of vessels communicate in the leaf by continuation of canal, as the arteries and veins do in animal bodies. In the stalk he considered them to be disposed in two concentric rings, the inner one of which carried out the sap to the leaves, and by the outer one it was returned to the bark. (Phytologia, p. 43 and 58.) In branches of the Apple and Horse-chesnut, Mr Knight also observed coloured fluids to rise through the vascular fasciculi in the petiole of the leaf. These fasciculi were surrounded by others free from colour, and which conveyed a different fluid, and, on being traced down the stalk, were found to enter the inner bark, and to have no communication with those of the wood. The returning vessels he describes as being situated parallel to, and surrounding those which carry up the sap. (Phil. Trans. 1801, p. 336.)

362. Beside the vascular system which thus, by its ramifications, forms the skeleton of the leaf, there is another structure that requires to be noticed. We have seen that the vessels, in their ultimate distribution, form a net-work, more or less fine and minute in different leaves; so that a great number of intervascular spaces are produced. These spaces, or areas, says Malpighi, are occupied by cellular tissue, which springs from the vessels themselves, and seems to depend from them, and by its means the thickness of the leaf is formed. In the recent part of the Borage-leaf, represented in fig. 13. Plate XVIII., this cellular structure, occupying the reticulated spaces formed by the vessels, is observed; but it is most clearly seen in thick leaves, when the cuticle has been removed, and the vessels in part dissected away. The cells or utricles which form this parenchyme, as it has been called, are of different figures, and are mutually contiguous; they are composed of a membrane formed into the shape of a little vesicle or bladder, from the middle of each of which, a little vascular production issues; they are all connect- Of Leaves, ed with each other, and with the vascular system of the leaf. In fig. 12. Plate XVIII. this cellular structure is represented in the leaf of Cactus by Malpighi, in which the oblong cells are described as proceeding from the central vessel, and mutually communicating with each other. (Anat. Plantar. p. 52.) A similar idea of the formation of the cells seems to have been entertained by De Saussure. In different leaves, the cells possess very different sizes and forms, and sometimes the sides of the greater ones are said to be made up of smaller. In the experiments of M. De La Baisse, they are said to have become tinged by coloured fluids conveyed from the vessels. Whether they communicate with each other is not known; but analogy, derived from other similar structures, would lead us to suppose that they communicate only with vessels, as seems to be the case in the cotyledous leaf of the seed.

363. Beside this cellular tissue, which forms so large a portion of the leaf, certain small follicles are described by Malpighi as being connected with it. Between the vessels and the cells of the parenchyme, in most leaves, variously figured follicles of this kind are stated to exist, from which a peculiar halitus or humour is discharged; their external orifice is bounded by a rising lip, and is often furnished with hairs. They are rendered more apparent as the more succulent parts of the leaf waste; and, in different leaves, possess very different forms. (Anat. Plantar. p. 52.) They appear to be the glandular organs, described as pouring out peculiar fluids on the surface of many leaves.

364. The whole structure of vessels and cells that constitute the leaf, is covered by a cuticle variously furnished with pores, hairs, and other appendages, as already described when treating of the cuticular texture.

365. To this division of our subject belong the small leaves called bracteae, stipulae, &c. which serve often but a temporary purpose to the flowers and leaves; and though of some importance in the descriptive details of the botanist, are but of small consideration with the anatomist. Like the scales that envelope buds, they probably derive their origin chiefly from the cortical texture.

Section III.

Of the Structure of Flowers.

366. The flower is understood to comprehend the organs by which fructification is accomplished, and those also which surround and protect them. These organs are the Calix, Corolla, Nectarium, Stamina, and Pistillum. The three first are not essential parts, but the two last are indispensable. All these parts are commonly borne on a stalk called the peduncle, which, expanding at its extremity, forms the receptacle, upon which all the other parts are supported. In fig. 1, Plate XIX., is the representation of a perfect flower, in which the principal parts above mentioned are exhibited. The letter a denotes the corolla, formed of six petals; b the stamens, c the pistil, and d the peduncle of the flower. In the next figure (fig. 2.), the corolla has been removed, and the parts within it are then more clearly displayed. At the base of the flower, the calyx (e) is seen: the pistil is composed of three parts, the ovarium (f), the style (g), and the stigma (h); the stamens are each distinguished into the filament (i), and the anther (k).

367. The flower, as well as the leaf, originates from a bud, and, in many respects, the buds of flowers resemble those of leaves; they are covered and protected in the same manner, but they are generally larger, and have a more rounded form. They consist of two parts, the gem or eye (oculus), as it is sometimes called, and the hybernaculum, or protecting envelopes. In some trees, they spring from the extremity of particular branches; in others, from the branches in common with the leaf-buds; in others, from the axils of the leaves; and in others, from the leaf itself—but in the same genus, the position of the flower-buds is uniform. In fig. 3. Plate XIX., is a portion of the branch of the Peach-tree, bearing two flower-buds (ll), between which the smaller and more pointed leaf-bud (m) is placed.

368. Grew discovered, and has exhibited many examples of the complete formation of the flower buds for many months before it is destined to bloom. (Anat. of Plants, tab. 63, 64.) Of this fact also, Du Hamel has given several examples. In fig. 4. is a longitudinal section of the flower-bud of the Peach-tree, made in the month of February, to show the complete formation of the stamens and pistils within the surrounding envelopes of the bud. In fig. 5. is another representation of a similar bud, from which the enveloping scales have been removed; it displays the calyx, which, at this period, completely envelopes the other parts of the flower. When the leaflets of the calyx are separated, as is done in fig. 6. then the stamens and pistils are fully disclosed; the petals also of this flower were visible, but at this period were very small. Even the anthers were found to contain a fine dust, but no rudiment of the future embryo could be detected in the ovary. In the flower-bud of the Pear, examined in February, the parts of fructification were also visible, but indistinct; a month later, all the parts were more advanced, and the stamens, petals, and pistils were distinct; and towards the end of March, even the rudiments of future seeds were visible in the base of the pistil. (Phys. des Arbres, Tom. I. p. 200.) Thus it appears, that, through the winter season, the several parts of the flower are clandestinely formed, though still extremely minute. As they enlarge, their position within the bud is very various in different species; they gradually expand, and form the perfect flower, whose several parts we have next briefly to describe.

369. The greater number of flowers contain both stamens and pistils, and are then styled complete or perfect; but frequently it is otherwise, and such flowers are deemed incomplete or imperfect. In most instances also, there is only one set of organs of fructification on the same flower, when it is deemed simple—in others, there are more than one, and it is named compound. Our limits will permit us to describe only one of these varieties, which we shall select from the division of complete simple flowers.

370. The peduncle of the flower, by which all the other parts are connected with the stem or branch, the Peduncle is frequently single, but often divides into several ele.

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Of Flowers parts or pedicels, as they are named, each of which supports one or more flowers. The modes in which the flowers are disposed on the pedicels, have received different names from botanists, and to the general circumstance they assign the term inflorescence. The peduncle, in structure, resembles the stalk of the leaf; being formed, like it, of the several common textures. In size, in length, and other external characters, it exhibits all the varieties already noticed in the petiole of the leaf.

371. At the extremity of the peduncle, is placed the flower-cup or calyx, which has very different forms, and has received, in consequence, different names. Even in its most common forms, it exhibits great variety. It is sometimes composed of a single piece, and has a tubular form; in others, of many pieces, which vary in number, position, and size, and for an account of which, we must refer to the writers on botany. In some instances, this organ falls when the fruit has set; in others, it continues till the fruit is mature; and in others, the fruit is formed within it, to which it becomes a permanent covering, and exercises the office of pericarp. The colour of the calyx is commonly green, but sometimes partly red, or white, or yellow. To some flowers it is entirely wanting. From the dissections of Grew and Malpighi, it appears to be constructed, like the leaves, of a cuticle, a pretty thick cellular tissue, and of vessels, all of which exist in the peduncle, and are derived from the common textures of the plant.

372. Above the calyx, the corolla, the chief ornament of flowers, is borne. It is enclosed by the calyx, but surrounds the interior parts of the flower, and is commonly of some other colour than green. It consists of one piece, or of several; these pieces are called petals, and according to the number of these pieces, the corolla is variously denominated. The monopetalous corolla, or that composed of one piece, is also distinguished into several parts, expressive of form, position, or quality; and in the polypetalous variety, which consists of several pieces, each petal has its claw (angulus) situated at the base, and by which it is attached to the calyx or receptacle, and its expanded part (lamina), which is of very various figure, size, and colour. At the base of the petal, a tuft of hairs is often observed, and their surface is frequently covered with a fine down, or sometimes with jointed hairs bearing globulets, as occurs on leaves. With regard to structure, Malpighi describes it as composed of the same textures as the common leaf, as is distinctly visible in the thicker varieties of it. Grew showed it to possess spiral vessels, a proof, as Du Hamel observes, that it is partly derived from the ligneous texture, since such vessels are not found in the bark. The odour these organs possess, leads to the belief, that they contain also a peculiar juice. (Phys. des Arbres, Tom. I. p. 215.)

373. The organ next to be noticed, is that called the nectary (nectarium.) It was observed and described by Malpighi, as a small organ situate at the base of some flowers, to which, from its figure, he gave the name of concha. Linnaeus considered it to be the organ which bears the honey, and as belonging to the flower only; but his descriptions of it are so exceedingly vague and inconsistent, that no attempt to define and exhibit its anatomical character can be made with any hope of success.

374. Having thus described the several parts that envelope the sexual organs, we must now briefly notice them; and first, the stamens.—These, in different flowers, vary greatly in origin, size, number, figure, and mode of attachment; and upon these differences, chiefly, the Linnean classes are founded. In general, each stamen is said to consist of two parts—the filament and the anther. The filaments exhibit various shapes, and are of very different size in different flowers; they are inserted occasionally into the corolla, the calyx, or even the pistil; but more commonly, like the calyx and corolla, are attached to the receptacle. Malpighi describes the filaments as originating from the ligneous texture, being formed of vessels and elongated cells. As they originate sometimes from petals, they must necessarily, he adds, be composed of the same parts (Anat. Plantar. p. 64.); and it is well known that, by culture alone, they are often reduced entirely to the condition of petals.

375. The anther is a little case or sac, formed by a thin but vascular membrane, and borne on the summit of the filament. It is filled with innumerable small particles, of various colour, size, and figure, in different plants, to which the name of pollen has been given. In fig. 9, A., is exhibited one of the filaments, bearing its anther, as it appears when detached from the pistil of the flower of Mallow, fig. 8, in which the particles of pollen are seen; and in fig. 9, B., these particles are represented as viewed by a still higher magnifying power. The anther itself is of very various size, figure, and colour, in different flowers; and its mode of attachment to the filament is not less subject to variation.

376. The pollen, contained in the anthers, is described by Grew as consisting of numerous regularly figured small particles, which, in different flowers, possess a very different figure, colour, and size. Many of their forms are delineated by Grew in table 58. of his work; and in fig. 10, Plate XVIII., several representations of these forms have been copied from Du Hamel. (Phys. des Arbres, Tom. I. lib. 3. Plate III.) The number of particles in each anther is very great, extending, it is said, from a few hundreds to several thousands. In some flowers, the pollen consists of transparent globules; in others, they are white, purple, blue, or brown, or more frequently yellow; their surface is either smooth or rough; they are regularly organized, and when examined under the microscope, may be seen to burst, and yield a fluid, in which, according to Du Hamel, small particles are seen to float. This fluid is represented as being sometimes thin, or viscid, or oily, and is said, by Hedwig, to be discharged at once on the bursting of the little capsule that contains it; while, according to Köclereuter, it is slowly transmitted through pores in the side, or hairs on the surface of the capsule. (Willdenow's Prin. of Botany, p. 310.)

377. The parts of the flower, hitherto described, are constructed, says Malpighi, with reference to the female organ, in which the seed, the last result sought by nature, is curiously formed, and carefully guarded. This organ, called pistillum, consists of Of Flowers, three parts, as represented in the pistil of the Almond-flower, fig. 11., in which the letter p denotes the stigma, q the style, and r the ovary. To this latter organ Malpighi gave the name of uterus; Linnaeus of germen; but we prefer the appellation of ovarium, assigned it by Gartner. Like the stamen, the pistil exhibits great variety in form, size, number, and mode of attachment; upon which, and other peculiarities, many of the orders, in the Linnean system of classification, are founded.

Its Ovary. 278. The ovarium, situate at the base of the pistil, differs greatly in size, shape, and structure, in different plants. It is the part in which the seed is formed, and, antecedent to fecundation, vesicles, which are the rudiments of future seeds, may frequently be detected in it. Its cavity consists often of but one cell or loculum, in which one or more seeds are produced; sometimes it is formed into many loculae, with which only one style communicates; and sometimes the several loculae have communication with distinct styles. Its structure will be noticed in treating of the changes of form it undergoes in consequence of fecundation.

Style. 379. The style, which is seated on the ovarium, and is commonly so situate in the flower, as to be surrounded by the stamens, exhibits, like all the other parts, the greatest diversity in all its external characters. It is commonly a hollow tube, which communicates, as observed above, with the ovary. Most commonly there is but one style to one ovary, but frequently more than one. In some instances, the pistils correspond in number with the loculae, into which the ovary is divided; in other instances, every seed that is formed has its distinct pistil connected with it; while, in other examples, only one pistil is allotted to a great number of seeds. In some flowers, there is no proper style, but the stigma is placed directly on the ovary.

Stigma. 380. The stigma, which forms the summit of the pistil, presents also the greatest diversities of appearance. It sometimes terminates the style by an open mouth; sometimes it appears like a small bud; in other instances, it is variously divided or forked; sometimes it is smooth, and is sometimes covered with hairs. The number of parts into which it is divided, corresponds, in many flowers, with the number of loculae in the ovary, as in the Liliaceae, the Umbelliferae, and others. (Phys. des Arbres, Tom. I. p. 225.) At the period of fecundation, the stigma is rendered moist by a peculiar secreted fluid. Its structure resembles that of the other parts of the flower, being composed of all the common textures, and a peculiar secreting structure. Some have professed to have discovered hollow channels in the stigma, which are described as being continued through the style to the umbilical cord of the seed; but this must be regarded as doubtful.

381. The foregoing descriptions apply, in detail, only to the more perfect flower, and that variety of it which is denominated simple. For an account of the numerous diversities of form, size, position, number, and attachment, exhibited in the sexual organs of the flowers of different classes and genera of plants, we must refer to the writers on botany; and to the works of Malpighi and Grew for the anatomy of many of them. We have room only farther to remark, that all the several parts of the flower seem very nearly to approximate in internal structure; for, under particular modes of cultivation, almost any individual organ may be made to lose its original character, and to assume that of any other.

Section IV.

Of the Structure of Fruits, and Formation of Seeds.

382. In the preceding section we described the structure of the flower, antecedent to fecundation; we have now to exhibit, as concisely as possible, the changes of form it undergoes after that event, and particularly as it regards the production of the seed.

383. After fecundation has been effected, the calyx, corolla, stamens, and even style of the pistil, commonly fade and fall; the ovary alone remains, and undergoes very different changes of form in different plants. In the latter periods of its enlargement, it is usually called pericarp (pericarpium), a term which is understood by botanists to apply also in certain cases to the calyx, the corolla, or any other apparatus of organs that serves as a support and defence to the seed. For an account of these varieties in the pericarp, and of the terms employed to express them, we must refer to the writers on botany, and more especially to the carpological labours of Gartner, who, in his learned and elaborate work, already so often referred to, has delineated the forms, and, to a certain extent, described the structure of the pericarps and seeds in more than 1000 genera of plants.

384. In its early state, the ovarium is described by Gartner as possessing at first a simple cellular structure, which, at a later period, assumes the form of distinct cells or loculae. Within these loculae, minute globules or papillae are afterwards seen, which are the rudiments of future seeds. At this period, they are mere pulpy globules attached to their containing cells, but, in some instances, approach to the character of small vesicles. So far the rudiments of the ovulum, like the entire bud, are produced without fecundation; but if that function be not performed, they scarcely acquire any increase, and at length spontaneously degenerate. The progressive series of changes that occur in the ovary itself, and in its contained ovulum, subsequent to fecundation, have been exhibited in the almond by Malpighi, whose observations we shall briefly detail.

385. In fig. 11. Plate XIX. is represented the pistil of the Almond, as it appears soon after fecundation, in which the ovary (r) is seen to be somewhat enlarged, and has an oval form. In the next figure (fig. 12.), a longitudinal section of the same pistil is exhibited, exposing the cavity of the ovary (s), within which a small vesicle (t) is placed. As the ovary (fig. 13.) enlarges, it becomes rounder, its style is contorted, and diminished in size. If in this stage it be laid open, as in fig. 14. its vessels, which, in the peduncle (w), are disposed cylindrically, are observed to be dilated at the place of the calyx (x), and to give off branches to the ovary itself, and to the shell (y) that now begins to be formed within it. In the centre, the ovulum (z) is now seen to be much increased.

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Of Fruits. All the parts continue to augment; the ovary (fig. 15.) becomes rounder, and the appearance of the style is obliterated. On exposing its cavity, as in fig. 16., the ovulum (a) in the centre is observed to be much increased, and the outer layer (b) of the shelly covering that invests it now begins to harden. Such are the changes of form and structure exhibited by the ovary: we have next to trace more minutely those of the ovulum that is produced within it.

Structure of the Ovulum.

386. The earlier appearances of this body have been exhibited in figures 12. and 14. When removed from its seat, a few days after fecundation has been accomplished, and viewed by a moderately magnifying power, it exhibits the form and appearance represented in fig. 17. Externally it is covered by a vascular tunic (c), derived from the inner coat of the ovarium, a part of which coat adheres to it at d. If in this stage the ovulum be laid open by a vertical section, as in fig. 18., it is seen to be composed of two tunics or sacs, one within the other; the inner one is filled with a cellular tissue that contains a transparent juice. To this inner tunic, the term chorion may be properly applied.

Its Chorion; chorion may be properly applied.

387. At a period a little later, when the ovulum is examined, a tubular body (e, fig. 19.) is observed to extend through the chorion or tunic last mentioned. Shortly after, this tube expands at its apex, and is found to contain a small vesicle. In fig. 20., which represents a section of the entire ovulum, the outer tunic, the chorion, and this tube (f), expanded at its apex, are exhibited. To it, the appellation of amnios may be given; for it is the organ in which the embryo, or rather the corelum, as at this early period it may be called, is first seen to emerge. Through several successive days, the expanded portion of this tube enlarges, and forms a sort of sac, which is filled with cellular tissue, and the summit of which, says Malpighi, the embryo is seen to occupy. In fig. 21., this amnios is separated from the other tunics, and, at its summit, the embryo (g) is observed. If removed from its seat, the embryo presents the appearance h (fig. 22.), and when expanded, as in fig. 22. (i), is seen to consist of a body and two little wings.

Its Embryo.

Growth of the Ovulum.

388. Having thus viewed the several parts of which the ovulum is composed in their separate state, let us next observe them in connection, and trace the series of appearances they exhibit, and the effects they produce on each other. In figure 23., is given a vertical section of the entire ovulum in a more advanced state; the outer coat (k) still envelopes the others; the embryo (l) occupies the summit of the amnios (m), whose lower part, still tubular, is continued through the chorion (n). In the next figure (fig. 24.), from which the outer coat has been removed, the embryo (o) and the amnios (p) are represented as enlarged; but the chorion (q) is partly exhausted of its juice, and has fallen down in a collapsed state. At this period, the embryo, when separated from the amnios, has the form (r) fig. 25., and in its expanded state is represented by the letter s of the same figure. The bulk of the embryo (t) fig. 26., continually augments, and encroaches on the capacity of the two tunics (v, x,) whose forms are constantly changing; and from being successively emptied of their juices, with which the embryo becomes filled, they are gradually pressed downward. At last, the embryo (y) of fig. 27., is so much augmented as to fill the cavity of the outer tunic, and by this time the amnios and chorion, exhausted of their fluids, exhibit the shrunk and corrugated forms in which they appear at the bottom of the figure. According to this representation, the outer tunic (k, fig. 23.), derived from the ovary itself, and the fine membrane that immediately invests the embryo, form the only permanent coverings of the mature ovum or seed; for during the progress of formation, the chorion and amnios, which are successively produced subsequent to fecundation, are again obliterated by the growth of the contained embryo. Malpighi describes the process of formation in many other seeds to be nearly similar; for his descriptions of which, we must refer the reader to his work. (Anat. Plantar. p. 71.)

389. In the above descriptions of Malpighi, the several parts seem to be clearly exhibited, except in one important particular, namely, the situation and course of the umbilical cord. In almost every instance, he designates the tube, which we have represented as the first form of the amnios, as the umbilical vessel (vasculum umbilicale), which the subsequent appearances it exhibits shows to be erroneous. In the descriptions of Grew, this deficiency in the representations of Malpighi is supplied. He has particularly observed the formation of the seed in the Apricot, which, in many respects, resembles that of the Almond; and we shall subjoin an abridged account of his observations.

390. In this fruit, the pericarp that envelopes the seed is seen, in its mature state, to be composed of three parts: the pulpy part (a) fig. 28., within which is the osseous envelope (b), and at the centre, the kernel or true seed (c). At an early period, both the pulp and stone are observed to consist of cellular tissue; and through the stone, the vessels, passing from the peduncle, are continued. At the base of the figure, the letter d denotes one fasciculus of vessels continued through the stone, and turning inward where it reaches the apex of the seed. These vessels form the umbilical cord or seed-branch of Grew, while the fasciculus (e) that runs on the opposite side, is continued to the flower. In fig. 29., a vertical section of the ovulum, as well as pericarp, is exhibited, as it appears at a very early period; in which f denotes the pulp, g the stone, through which the umbilical vessels pass and enter the outer tunic (h) of the ovulum, around which they make a ring. Within this tunic is another (i) filled with cellular tissue, and through its axis a small tube extends, at the apex of which the embryo (k) is first seen to emerge.

391. In fig. 30., these several parts of the ovulum are exhibited on a larger scale; the letter l denotes the outer tunic that immediately lines the stone; m the inner one, corresponding to the chorion of Malpighi; and n the tube answering to the amnios of the same author. Through the outer tunic, Grew represents the umbilical vessels to pass and be continued to the middle tunic; the cavity of which is occupied by large cells that contain a pure lymph. At first this tunic is entire, but soon there appears in it the small duct (n). This duct is not at first

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Of Fruits. wider than a hair, and is dilated at each extremity into an oval cavity that contains a pure lymph. A few days after, a soft node is seen to emerge in the upper cavity of this tube. This node (o) fig. 31. is described to possess a conical figure, and to be another tunic filled with very minute cells. It is at first entire, but when about the size of a Carraway-seed, it becomes a little hollowed near its apex, at which part the vessels enter and terminate in another very small node, fig. 32., which is the first appearance of the embryo of the seed. This embryo, when about one-fifth part as big as a cheese-mite, begins to be distinguished by a little fissure, which marks the division of the lobes, as in fig. 33. When the lobes have increased, and are more fully formed, the node contracts at its base, fig. 34., indicating the place of the umbilical cord, which subsequently becomes the radicle of the seed. (Anat. of Plants, p. 209.)

392. This description corresponds nearly with that of Malpighi as far as regards the situation and general form of the tunics, and the place in which the embryo is seen first to emerge. It also displays the course of the vessels to form the umbilical cord; but the growth of the embryo in this seed, does not seem to produce the obliteration of some of the tunics in the manner delineated by Malpighi.

Structure of the Pear. An example of a different kind is observed in the Pear. Its structure has been described by Grew, and more minutely by Du Hamel. In its mature state, it consists of a pulpy matter, in the centre of which are five loculae that contain each two seeds. These appearances are exhibited in the transverse section, fig. 35.; and in the longitudinal section, fig. 36. the seeds are further shown to be attached by a small umbilical cord. The pulp of the fruit is made up of a very fine cellular tissue, filled with the proper substance of the fruit, and is everywhere furnished with vessels. Through this pulpy matter a number of solid particles are met with, which are more particularly accumulated at the top and about the core. They are formed of an assemblage of small particles, of a stony consistence, with which a little knot of vessels (fig. 37.) is everywhere connected. In fig. 38. is a thin transverse slice, showing the relative position of these stony particles, as indicated by the knots of vessels with which they are associated. The stony matter is not observed at an early period, but seems to be deposited from the juices in a more mature state.

394. By long maceration in water, the pulpy matter is dissolved, and the vascular system is obtained separate. In the peduncle of the fruit, fifteen principal fasciculi of vessels are contained. Ten of these are distributed to the seeds and flower, and the five others are dispersed through the pulp. This vascular structure is represented in fig. 39. after the removal of the pulpy part; the larger vessels embrace the core, and, after variously ramifying, terminate in the little vascular processes before described as connected with the stony matter of the pulp. In fig. 40. is represented one of the loculae of the capsule, with the seed in it, receiving vessels from fasciculi continued from the peduncle; and in fig. 41. an entire seed is represented, and also a section of the same, in which the umbilical vessels that enter at the base are shown, as in other instances, to be continued, beneath the tunic, to the apex of the seed. (Phys. des Arbres, Tom. I. p. 242.)

395. The last variety we shall notice in the Ovulum of formation of the seed, is that of Wheat (triticum), Wheat, as given by Malpighi. In fig. 42. A. is represented the pistil of the flower of this plant, consisting of the ovarium (q), the two styles (r), and the feathered parts that form the stigmata. Previous to fecundation, the ovarium is found to contain a little vesicle, fig. 42. B. which is the rudiment of the future ovulum. After fecundation, the styles soon fall, and the ovarium acquires a more pointed figure, as in fig. 43. If now it be opened, the little vesicle has changed its appearance, and contains within it another smaller vesicle (u), fig. 24. The ovarium continues to alter its shape, and assumes a more oblong form, fig. 45. and the appearance of styles is now quite obliterated. Gradually the little vesicle is formed into a small plantule, convex anteriorly, fig. 46. but more hollowed within, fig. 47. and which is situated at the base of the ovarium. The two portions thus described in figures 46. and 47. are the minute germ and cotyledon of this seed, which are represented in their appropriate place in fig. 48., in which the letter x denotes the germ, resting in the concavity of the cotyledon; y the albumen that forms the chief bulk of the seed; and z the ovarium which, in this seed, continues permanent, and forms its outer tunic. (Anat. Plantar. p. 73.)

396. We have thus, in different examples, exhibited the structure of the seed; have followed the changes of form displayed in its evolution; and, in various instances, have demonstrated the construction of the several members of which the mature plant is composed. We have then described the formation of buds on the trunk, the branch, and the root, and displayed their structure in the successive stages of their evolution, by which not only new roots and branches, but leaves and flowers, are produced; and, lastly, we have followed the changes of form and condition manifested in the flower itself, from which a new seed originates, fitted to undergo and exhibit the same series of changes.

The external agents required to the accomplishment of these various changes, the circumstances in which they act, and the modes of their operation, belong to the department of Physiology, and will form the subjects of future consideration. (a.)

INDEX. ## Index

| Topic | Page | |----------------------------------------------------------------------|------| | Absorption, function of | | | - external | | | - internal | | | Apricot, structure of | | | Albumen of seeds | | | - contained in cells | | | Bark, description of | | | Bean, structure of | | | Branch, description of | | | - origin of | | | - elongation of | | | Buds, definition of | | | - species of | | | - description of | | | - formation of | | | - structure of | | | - evolution of | | | Bulbs, structure of | | | Cellular tissue, description and structure of | | | Cells, communicate with the vessels | | | - have no pores | | | - structure and formation of | | | Claspers, structure of | | | Corculum of the seed | | | Cotyledons, description and structure of | | | Cuticle, description of | | | Embryo of seeds | | | Exhalent system | | | Fern-seeds, evolution of | | | Flowers, parts of | | | - structure of | | | Fruits, formation and structure of | | | Germ of buds, origin and structure of | | | Glands, ambiguity of the term | | | - species of | | | Gourd-seed, evolution of | | | - plantule, structure of | | | Hairs, varieties of | | | - structure of | | | Herbs, structure of the stem of | | | Leaves, description of | | | - parts of | | | - origin of | | | - structure of | | | Members of vegetables, anatomy of | | | Moss-seeds, evolution of | | | Nucleus of seeds, description and structure of | | | Organs, elementary, anatomy of | | | - individual, anatomy of | | | Oak, structure of its wood | | | Ovary, structure of | | | - changes in, from fecundation | | | Ovulum, structure of | | | - growth of | | | Palm-tree, structure of | | | Pea-seed, evolution of | | | Pea-plantule, structure of | | | Pear, structure of | | | Petiole, structure of | | | Pith, description of | | | Pores of the skin, description of | | | - air and light favour their production | | | Prickles, definition of | | | - structure of | | | - in the nettle | | | Rootlets, origins of | | | - structure of | | | - are annually renewed | | | Roots, varieties of | | | - of trees, structure of | | | - of herbs, structure of | | | - tuberous | | | - growth of, modified by soil | | | Sap, course of in the wood | | | - in the bark | | | - modified by the leaves | | | - qualities of, changed in the leaves | | | "Proper," collections of in the cellular tissue | | | Seeds, description of | | | - coats of | | | - nucleus of | | | - monocotyledonous, evolution of | | | - dicotyledonous, evolution of | | | Skin, description of | | | - regeneration of | | | - structure of | | | - its pores | | | Stem of herbs, structure of | | | Sugar-cane, structure of | | | System, vascular | | | - absorbent | | | - exhalent | | | Textures, common, anatomy of | | | - medullary | | | - ligneous | | | - cortical | | | - cuticular | | | Tissue, cellular, description of | | | Trunk in shrubs and trees, structure of | | | Thorns, origin and structure of | | | Tendrils, origin and structure of | | | Vessels, general characters of | | | - common sap | | | - spiral | | | - transformations of | | | - structure of | | | - Proper, description of | | | - structure of | | | Vitellus of seeds, description of | | | Wheat-seed, evolution and structure of | | | - peculiarity of structure in | | | - formation of | | | Wood, description and structure of | |