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Grew and Malpighi, do indeed, represent them as occurring often in the root, the former refering for examples to the roots of plants in general, and the latter to those of the asparagus, poplar, convolvulus, elm tree, and reed; all of which, Keith says, I have examined with great care, without being able to discover any spiral tubes. Senebier says he found them in the root of the balsams and thorn-apple; in examining which I was equally unsuccessful as in examining the former. I cannot, however, doubt the accuracy of the observations of the above phytologists, and can only set down my own want of success in discovery to the score of some defect, either in the specimens examined, or in my mode of examination. Indeed, the only root in which I have ever found them, after examining a very considerable number, is that of the common garden lettuce, know by the name of cos lettuce. Having taken the root of a plant that was just putting out its flowers, and stripped it of its bark, I then cut it partly across, about the middle of its length, and broke the remainder of it gently asunder. On examining the surface of the fracture with the microscope, fragments or spiral tubes were seen projecting from it near the centre. They did not seem very tenacious of their spiral form; and when once uncoiled did not readily resume it.'

151. The spiral threads are to be found also in the stem and branch; but not in all parts of them; or at least not in all periods of their growth. It seems very doubtful, whether they exist at all in the bark. Daubenton professes, indeed, to have seen them in it; but no one else ever has; so that we are, perhaps, sufficiently well warranted in entertaining our doubts. It seems also very doubtful, whether they exist in that part of the stem which consists of matured wood, though Daubenton professes to have seen them in the wood of cedrela; in which case he does not altogether stand alone; as they are represented both by Grew and Hedwig, as visible also in the wood. But they have not been found in the matured wood by any other vegetable anatomists. Du Hamel never met with them in any of the woody parts of woody plants, except in the young and herbaceous branches. Mirbel expresses himself to the same effect. And Mr. Knight, who has examined the subject perhaps still more recently, could not detect them in any of the permanent parts of such plants, except in the annual shoot. Keith's observations on this subject have had nearly a similar result. Among many subjects of examination he mentions only the elder, willow, hawthorn, cherry, and elm tree. In the three former, he found them only in the annual shoot, situated immediately without the pith, or rather imbedded in the alburnum; though in the elder some of them seemed to be imbedded even in the pith itself. In the cherry he found also a very few, similarly situated, in the branch of two years old; but none in wood older than that. And in the elm tree he has thought he had discovered them even in the matured wood. Having placed under the microscope a very thin slice, taken from a piece of the trunk of an elm tree, that had been felled at least six or seven

years, he thought he was able to trace the remains of the spiral tubes. The slice was taken from the surface of a longitudinal section passing through the centre of the trunk, and clear of divergent layers; and the tubes seemed to appear most distinct when the slice was so placed as to present their longitudinal dimensions to the light. They seem to resemble ribands wrapped spirally round a cylinder, rather than to form separate vessels, which corresponds very well to their appearance, even in the succulent parts of many plants, as described by Knight. Some of them seemed even separate and entire. And yet, upon repeated observation, he has not been able to satisfy himself entirely on this point; but he has stated the case circumstantially, as being the probable means of inducing some one to take up the subject, who may be more felicitous in his investigations. It cannot be said to be a vain or fruitless enquiry. For as they are known to have existed at least in the tender shoot, it will follow that they must exist, in one shape or other, in the matured wood also. And if their spiral form is there obliterated, under what other aspect do they now appear? It seems certain, from the observations of Hedwig, that they assume a different figure in different stages of the plant's growth. In the peduncle of the colchicum autumnale, the rings of the tubes are closer when it begins to appear above ground, than at the time of flowering, from which he concludes, that they are at length entirely obliterated, and the tubes converted into woody fibre. But sometimes it is difficult to detect them, even in the young shoot; though they are generally to be observed by breaking it gently asunder, and then examining the surface of the fracture with a microscope. In this case they appear in small fragments, projecting from the surface, and somewhat uncoiled; but if the shoot is split longitudinally, a portion of them will sometimes be found extended longitudinally on the surface of the fissure in an uncoiled state.

152. In the stem and branchcs of herbaceous plants, they are generally discoverable, without much difficulty, accompanying the longitudinal fibres, and forming part of the bundles. Keith has found them in the stem and branches of the burdock, even in winter, when the fragments of the mature plant had become quite indurated by means of their exposure to the weather.

153. They are also very easily detected in the foot-stalk, both of the leaf and flower, accompanying, or rather seeming almost entirely to compose, the bundles of longitudinal fibres. This may be well exemplified in the leaf-stalk of the artichoke, when young and fresh, in the fibres of which they are not only remarkably large and distinct, but also remarkably beautiful; some of them exhibiting in their natural position the appearance of spiral coats, investing interior fibres, rather than that of forming a distinct tube, and seeming when uncoiled to be themselves formed of a sort of net-like membrane.

154. They are discoverable also in the leaf, though not quite so easily detected as in the leafstalk. But if a leaf is taken and gently torn asunder in a transverse direction, fragments of the spiral tubes will be seen projecting from the

torn edges, and generally accompanying the

nerves.

155. They are also to be found both in the calyx and corolla, but not so generally as in the leaf, on which account some botanists have decided rather too hastily with regard to their non-existence in these parts of the flower. Mirbel says, no trachea are to be found in the calyx nor in the corolla, except in the claw. But Keith has found them most unequivocally in the calyx of scabiosa arvensis; and also in the expansion of the corolla of the same plant, as also in the calyx, both proper and common, of dipsacus sylvestris, and in the corolla of the honeysuckle, in which they appear to be placed within the nerves, or at least to be closely united to them.

156. In the other parts they do not seem to occur frequently, or at least it is difficult to detect them. Malpighi represents them, indeed, as occurring in the stamens, but Keith was not fortunate enough to meet with them in the stamens of any flower he examined. He looked for them also in the style of many flowers, and found them in that of the honey-suckle only.

157. According to the observations of Grew and Malpighi, they are to be met with both in fruits and seeds; though Hedwig says, they are not to be seen in the cotyledons, except during the process of germination, and that only by means of their being moistened with some colored infusion. But Gærtner says, they are conspicuous in the thinner cotyledons, even before germination takes place; and Reishel is said to have detected them even in the plumelet and ra

dicle.

158. But, in whatever part of the plant they are found to exist, they are always endowed with a considerable degree of elasticity, as has been already noticed. For though they are forcibly extended, so as wholly to undo the spires, they will again contract, and resume their former figure, when the extending cause is withdrawn; and if they are even stretched till they break, the fragments will again coil themselves up as before. It has been said, however, that those of the butomus umbellatus, if once uncoiled, will eontract again no more. But this is true only when they are stretched to a great length. For when they are stretched gently and moderately, they will again contract, as has been proved by experiment.

But

159. Malpighi, in the course of some observations on the spiral tubes during the winter season, fancied he had perceived a sort of vermicular and spontaneous movement in them. he thought he saw this movement only once, and as it has never since been seen by any subsequent observer, it appears that we must be content to set it down to the score of microscopical deception, or to the effect of the atmosphere upon the tubes when exposed to its action.

160. We have now run over the differences of the most important kind, by which the functions of what Darwin not inaptly called the viviparous system of vegetation, are affected. Let us now proceed to consider the nature and destination of the oviparous system, or of the parts of reproduction by seed. As the former depend upon

internal organisation, so do the latter upon external peculiarities.

161. Hitherto we have scarcely spoken of the flower; that brilliant ornament of plants, which attracts admiration by the splendor of its colors, and the delicacy of its texture, by the delicious perfume which it exhales, and by the wonderful mechanism with which it is constructed. Its base, which acts as an external envelope, is ordiarily of a green color, and is called the calyx. The next envelope, which is the most striking, as it is in it that the beauty of the flower resides, is the corolla. Then succeed the stamens, which are generally delicate threads, terminated by a dilatation of a particular nature; and the pistillum, consisting of ovarium and stigma, which in time becomes the fruit. These parts generally exist all in a single flower, which is then termed complete; if a part of the members is absent, the flower is termed incomplete. Each organ is susceptible of an infinite variety of combinations and modifications in form, in number, in station, in proportion, or in structure, which give rise to the smaller divisions of vegetables called genera. These will be noticed hereafter. The functions only of the organs are to occupy our attention while treating of Vegetable Physiology.

162. The most easy to observe is the corolla; which is composed of one or more pieces called petals; in the former state it is monopetalous, in the latter polypetalous. The petals are either equal or unequal in their form or insertion, whence corollas are either regular or irregular.

163. The stamens appear, from their position, to bear a direct relation with the corolla; thus, in almost all monopetalous flowers, they originate from the corolla itself; but in polypetalous flowers this more rarely happens; then, however, they maintain so many relations with the petals, being alternate or opposite to them, and equal or double or multiple in number, that it is impossible to doubt of the strict alliance by which they are connected. The calyx has a yet more strict analogy with the corolla, the divisions of which are almost always equal in number to those of the calyx, and alternate in insertion, especially when the corolla arises immediately from the calyx. It often happens that it arises from a particular place which is called the receptacle. These three parts, then, have a great analogy with each other; so that one does not vary in the number of its divisions, without affecting the two others by the change. They are themselves, however, subordinate to the pistillum.

*163. There is generally only one pistillum in flowers; occasionally two or more: but these variations in number are independent of the other organs. The ovarium has then a more obvious relation: it is seated in the centre of the flower, at the bottom of the calyx, to which it is attached by its base; sometimes a cohesion takes place between the sides of the calyx and ovarium, which latter then appears to support the flower like a footstalk. From these two modifications arise those two important distinctions among plants, of ovarium superius, or separate from the calyx, and ovarium inferius, or adhering to the calyx; differences which are of extreme importance in

characterising many of the most natural of the systematic combinations of modern botanists.

164. In some flowers the corolla disappears, or is not developed, in others the calyx seem to be wanting. Touching this fact, has arisen a disquisition, which seems to have no end, as to what name ought to be applied to the envelope of a flower when one envelope only is present. By whatever name this single envelope may be called, it bears the same relation to the other parts as the calyx and corolla when both are present; it is in some cases itself almost obliterated, and there are some flowers which consist only of stamens without corolla, and which are then called naked.

165. When both calyx and corolla exist together or one of them only, another set of organs occasionally disappears, namely the stamens, and then the pistillum is found alone in the centre; but in this case it always happens, that, either upon the same plant or upon a different individual, flowers exist which contain stamens only, and no pistillum. Sometimes both organs are developed without covering, and separate from each other. However these two parts may be separated from each other, they always appear at the same period of time, and, ever since the study of plants has been an object of philosophical research, no instance has been found of a perfect plant in which both organs did not co-exist.

166. It appears therefore, from this example, and from many others which could be brought forward, that the stamens and the pistil are the only essential parts of a flower; a fact which is not surprising as far as the pistil is concerned, because we have seen that it contains the rudiments of the future progeny. But what manner of influence is exercised by the stamens? If we examine them in every flower within our reach, we shall find that they have a similar structure: we shall see that they consist of two parts, the upper resembling a little bag, generally yellow, and always divided into one or two cells, which contain a kind of powder, and the lower resembling a thread-like stalk to the former. The former is called the anther, and the latter the filament. The powder which it contains, examined through a microscope, consists of granules, varying in size and form according to their species, and sometimes so remarkably, that it is often possible to distinguish genera by the inspection of the granules only. Thrown into water they swell, and eventually burst, emitting a peculiar fluid which resembles vapor. The name given to the granules is pollen.

167. From the combination of these observations, we come to an important discovery; we perceive that the petals, with the brilliant tints of every color of the rainbow, are in fact the curtains of the nuptial bed of Flora, within the protection of which the mysteries of generation are accomplished. We have, therefore, sexes in plants; these, indeed, appear almost indispensable. In most animals they are separated; but in vermes we see them confounded, and at length disappear entirely. The want of the power of motion in vegetables renders their union in one individual of great importance. But, as if the resources of nature were illimitable, they are in

some cases separated upon the same tree, or upon different trees, and the agency of the wind or of insects, is requisite to enable them to accomplish their destiny.

169. The relation, therefore, of the stamens to the pistillum, gives rise to some further considerations. When they are united in one flower, the flower in that case is called hermaphrodite; if they are in separate flowers, it is declinous; it is monoecious when the male and female are present in different flowers of the same individual; dioecious, if in flowers of different individuals. Some plants have male and female flowers mixed with such as are hermaphrodites; then they are called polygamous.

14. The pistillum offers a multitude of most important characters. Its ovary is terminated by one or several styles, and each of the latter has one or more stigmata. The ovarium either contains only one rudiment of a seed, called an ovulum, or several, and is divided internally into one cell or many.

170. The fruit, which is the necessary consequence of the ovarium, is generally like it in the number of its parts; the occasional abortion of some one of the latter, is the only way in which the number of parts is smaller in the fruit than in the ovarium. The form, the texture, and the volume of fruit give rise to an infinity of differences. Thus one sees, on the one hand, soft pulpy fruit, and, on the other hand, nuts, the shell of which is hard as wood itself. The manner in which the seeds are attached is also subject to variation, for they either proceed from a central receptacle, or from the paries of the fruit. The point from which they proceed is, in all cases, called the placenta. This organ is of great importance; for it is not only the medium through which the fecundating effluvia of the pollen is communicated to the ovula, but also through which the juices are elaborated, which are required for the development of the embryo. It may be compared to the placenta of animals. .171. The position of the embryo, with relation to the fruit, is also a point of importance. Thus the axis of the seed may be parallel with the axis of the fruit, and fixed by the basis, which is the most natural position; then the seed is called erect. It may become horizontal; or being affixed to the summit of the cell it may become inverted; it is in the latter case said to be pendulous. For various modifications of the position of the seed, see SEED, under PURE BOTANY.

172. Each seed may be considered as an isolated individual; for nature has prepared them for separation from their parent without inconvenience. Their interior consists of a substance of various degrees of texture, which is called the albumen, and of the fleshy body already mentioned as the seminal embryo. The albumen may be absent, the embryo must be present. The coat of the seed consists of two layers, the interior of which is much more membranous than the exterior.

173. But now arises a problem in vegetation which it is very important to resolve. Whence is the origin of the flower? Linnæus has offered an explanation, which he considered capable of of meeting every difficulty, and which he bor

rowed from Casalpinus, whose knowledge ran far beyond that of his age. According to these two authors the flower is only a manifestation of the interior of a plant. The epidermis and cuticle give rise to the calyx, the fibre to the corolla, the woody fibre to the stamen, and the pith to the pistillum; this last part is the most essential, and the centre of vegetation; the others are only accessory.

174. But this ingenious notion, like many other brilliant hypotheses, will not bear a strict scrutiny. The nature of the pith is now better understood, and instead of being a creating organ, it is itself, in fact, a body in a state of disorganisation. A single fact has overthrown the whole theory this is the more intimate knowledge of the interior of palms, and other monocotyledonous trees. According to the arrangement of their interior, and the mixture of the pith and woody fibre, it would happen, if Linnæus's theory were true, that the flowers of the palm would have quite another arrangement from that of other plants, and that the parts would neither be arranged round a centre, nor be placed in the same relation to each other.

175. It appears certain, that, notwithstanding the striking differences which all parts of a flower exhibit, they have all the same origin; which is indicated by the propensity they all have, under certain circumstances, of changing into each other from circumference to centre, or of reverting to one common appearance; which is that of the leaf.. Upon this subject Mr. Lindley remarks, that it is well understood that the universal principle upon which perfect vegetables are formed, is by the continual addition of parts one above the other, round a common axis, which is produced by their accretion. This law is not confined to the production of foliage, or branches only, but must be considered to extend to the ultimate point of vegetable development in the ovarium; and seems to indicate that the progress of nature is continually onwards. Unless, therefore, it should be shown that the order of alteration in the structure of organs so produced is in monstrous formations reversed, it would be a reasonable inference that nature follows her usual course in transformation, as well as in original production; and that the changes which particular portions of a flower may undergo, always have the character of that series which is placed next them in the inside, and not of that on the outside. The consequence of the prevalence of such a law would therefore be this, with respect to the formation of double flowers, that bracteæ, if present, would change into calyx, calyx into petals, petals into stamens, and stamens into ovaries; and that the reverse of that order could not take place.'

176. It may thence be concluded that a flower is a leaf-bud in a particular state of alteration; that the calycine lobes, the petals, the stamens, the pistillum, are all leaves in an altered form, and that they have all a tendency, which may now and then manifest itself, of assuming their primitive habit and structure. Whence they arise, or in what way this extraordinary metamorphosis takes place, we are as yet unable to determine.

177. The pistillum, which is the terminating point of the line of vegetation, is now ascertained to be, not, as was formerly supposed, an anomalous organ, which was referable to none of the simple types upon which the other parts of fructification are modelled, but a leaf or leaves also in a state of greater affinity to their type than any other organ. The style is an alteration of the middle nerve, the stigma a secreting surface proceeding from the tip of the same part, the sides of the ovarium the two halves of the leaf, and the placenta the edges of the leaf. This is tolerably obvious in a strictly simple unilocular ovarium, such as one segment of a Pæony fruit. But in a many-celled pistil it is not so apparent. Mr. Robert Brown, however, has demonstrated, that all multilocular compound ovaria are merely an aggregation of a number of simple ovaria round a common axis; that the cells are occasioned by the interposition and cohesion of the sides of simple ovaria, which in that state are called dissepiments.

178. Besides the plants which are furnished with a flower, there are others in which no apparent flowers exist, which are constructed differently from either monocotyledonous or dicotyledonous plants, and whose methods of reproduction are quite of another nature. These plants are called cryptogamous, and consist of ferns, mosses, hepatica, lichens, algæ, and fungi. They are all supposed to be destitute of cotyledons, whence they are also named acotyledonous.

179. In ferns, which are by some authors referred to monocotyledons, the mode of growth resembles in some measure such plants. The grain from which they are reproduced, and which is called a sporule, in germination dilates into a very small leaf of a particular kind, which successively gives rise to others, which finally acquire the stature and the form of adult leaves. A species of trunk or stipes, similar to that of the palm, creeps along the surface of the earth, or elevates itself above it. Its internal structure separates it as far from monocotyledons as from dicotyledons. It has, however, at the first sight, the greatest resemblance to the former; a section of it offers, as in monocotyledons, certain scattered points, among a mass of parenchyma. These points, which vary in almost every different species, are a section of a peculiar substance, which is divided at the base, and united at the summit, and which may be compared in texture to the liber of dicotyledons. It is surrounded by a fur, which is more or less apparent, and more or less deeply colored, and which seems analogous to the woody texture, especially as in arborescent ferns it is it which forms the solid substance. Both these substances are distributed among the nerves of the leaves, which are simple, ramified, or verticillated, according to the species. In the opinion of a celebrated modern physiologist, a fern may be considered as a plant turned inside out.

180. The remaining classes of cryptogamia consist entirely of cellular tissue, amassed in different proportions, and under various forms. They are destitute of woody vessels or of trachea, and have no distinction between bark, wood, and epidermis; they may perhaps be considered

to consist wholly of the latter and former confounded.

IV.-PURE BOTANY.

181. We have thus considered botany with respect to its analogies, its history, and its physiology. It now remains for us to explain its practical details, as applied to what is called SYSTEMATIC BOTANY, or the science of arranging the natural objects of which it consists.

182. The materials of this branch of the science are the modifications of parts; from a just application of these materials result classifications. We shall first attend to modifications.

183. All perfect plants consist, as has been already seen, of the following organs. 1. The ROOT; 2. the STEM; 3. the FOLIAGE; 4. the INFLORESCENCE; 5. the FLOWER; 6. the FRUIT. Each of these organs must be considered separately. But, before entering upon an explanation of the peculiarities of each of them, it will be proper to notice the terms used in speaking of their size, surface, and color; these terms being applicable to each of the six parts into which a plant is divisible.

184. There are eleven terms which are employed to designate the size or measurement of a plant or its parts, viz.:

1. A hair breadth (capillus), the measure of a hair, or the twelfth part of a line.

2. A line (linea), the length of the white crescent at the root of the nail of the middle finger, or the twelfth part of an inch.

3. A nail length (unguis), the length of the nail of the middle finger, or half an inch.

4. An inch (pollex, uncia), the length of the first joint of the thumb, the twelfth part of a foot.

5. A hand breadth (palmus), the breadth of the four fingers of the hand, or three inches.

6. A span (dodrans), as far as one can span with the thumb and the little finger, or nine inches.

7. A small span (spithama), as far as one can span with the thumb and fore finger, or seven inches.

8. A foot (pes), the length from the elbow to the wrist, or twelve inches.

9. A cubit (cubitus), from the elbow to the point of the middle finger, or seventeen inches. 10. An ell (ulna, brachium), the length of the whole arm, or four and twenty inches.

11. A fathom or toise (orgya), the length of the arms stretched out from the tip of one middle finger to that of the other, or six feet.

For these the following have been substituted by some French botanists:The millimètre of a line. The centimètre 4 lines 43

The decimètre 3 inches 8 lines. The mètre 3 feet 11 lines T000 185. The surface of plants is of great importance in distinguishing the species and varieties of plants, but is not of value in generic discrimination. The terms which follow are, or ought to be, used precisely in the sense here ascribed to them; they are extremely well defined by Willdenow, who limits them thus:

1. Shining (nitidus), when the surface is so

smooth that it reflects the rays of light, and has a shining or glancing appearance, as in the leaves of the holly, Ilex aquifolium.

2. Dull (opacus), when the surface does not reflect the rays, and is entirely void of lustre. 3. Even (lævis), without striæ, furrows, or raised dots. It is the opposite of Nos. 6, 7, 23, 24, 25, 28, and 29.

4. Smooth (glaber), when there are no visible hairs, bristles or thorns. It is the opposite of Nos. 8, 22, 26 and 27.

5. Dotted (punctatus), where small fine dots are perceived by the eye but not by the touch. Thymus vulgaris.

6. Scabrous (scaber), where small raised dots are felt but not seen; as in Carex acuta. 7. Rough (asper), when these dots are both felt and seen. Pulmonaria officinalis. 8. Hispid (hispidus), beset with very short stiff hairs. Myosotis arvensis.

9. Hirsute (hirtus), where the hairs are moderately long but very stiff. Echium vulgare. 10. Hairy (pilosus), beset with long single hairs, somewhat bent. Hieracium pilosella. 11. Villous (villosus), where the hairs are long, soft, and white. Stachys Germanica.

12. Pubescent (pubescens), overgrown with short fine white hairs. Oenothera mollissima.

13. Silky (sericeus), when the surface is white' and shining, by means of thick and almost invisible hairs. Potentilla anserina.

14. Woolly (lanatus), when the surface is beset with long thick white hairs, easily distinguished. Stachys lanata.

15. Tomentose (tomentosus), when fine hairs are so matted together that the particular hairs cannot be distinguished. In this case the surface generally appears white, as in Verbascum; or of a rust color, as in Ledum.

16. Bearded (barbatus), when the hairs are in tufts. Mesembryanthemum barbatum.

17. Strigose (strigosus), when the surface is armed with small, close-lying bristles, which are thickest below. Lithospermum officinale.

18. Stinging (urens), when a painful burning sensation is caused by small hairs. Urtica. Such hairs are called stimuli.

19. Fringed (ciliatus), when on the margin of a leaf, or the surface of a stalk, there is a row of hairs of equal length.

20. Warty (papillosus), when small fleshy warts appear. Aloe margaritifera.

21. Pustular (papulosus), when there are small hollow bladders. Mesembryanthemum hispidum.

22. Muricated (muricatus), armed with small short herbaceous spines. Asperugo procumbens.

23. Scaly (lepidotus), when the surface is covered with small scales closely placed, by which means the color is changed, as in Elæagnus angustifolia.

24. Mealy (farinosus), when the surface is thickly covered with a white powder, as in Primula farinosa.

25. Hoary (pruinosus), when the surface is strewed with a very fine white dust, like the fruit of some plumbs. Prunus domestica.

26. Glutinous (glutinosus), when the surface is covered with an adhesive matter, which is soluble in water. Primula glutinosa.

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