The sylva americana; or, A description of the forest trees indigenous to the United States, practically and botanically considered

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Part I. Vegetable Physiology

By a vegetable, we mean an organized body possessing vitality, power of growth and reproduction, deriving its nourishment directly from the earth, or from substances in which earthy matter is more or less present, but without perceptive powers, or voluntary locomotion; the two latter properties belonging exclusively to animals, and forming the principal line of distinction.

Hence every living substance of the above description, whether it be a tree, a shrub, an herb, a grass, or a flower, is in reality a vegetable; and the whole, taken together, constitutes what is termed the vegetable kingdom. Of these, nearly one hundred thousand species, each possessing its own peculiarities, form and laws, have already been discovered, and the list is annually increasing. ‘The subject, therefore, independently of its practical application, is one of deep interest and importance ; and the moré it be examined, the greater field we find for inquiry, and an increased reason for admiring the contrivance, wisdom and benevolence, by which this interesting portion of the universe has been regulated.

To describe each particular organ of a vegetable, is denominated the anatomy, and to enter upon the functions of those organs with the results, the physiology of vegetables. 'To explain their component or constituent parts, belongs to the province of vegetable chemistry. And to treat on the sources by which their growth is promoted, and their productions increased, comes under the head of chemical agriculture, or agricultural chemistry.

From the great similarity and strong analogy of the laws of the vegetable and animal kingdoms, many modern philosophers have considered the vegetable and animal kingdoms united by one link, and forming a part of the same system; or, in other words, that a vegetable is only an inferior order of animal. But admitting how nearly in many instances the laws of each approximate, and how greatly a knowledge of the one facilitates that of the other ; yet the more frequent presence of perceptive powers, and more especially of a choice and capacity of motion in the one kingdom, and a total abstinence of those qualities in the other, present so broad and strong line of distinction, as should make us pause before we admit a doctrine directly at variance with our common observation, and so opposed to the idea we have entertained of the intents and purposes of creation. All that we ought to allow, is that resemblance only in the physical properties and laws of the two kingdoms, by which the vitality peculiar to each is preserved, the different parts are nourished, growth promoted, secretions produced, reproductions effected, and the common principles of decay and dissolution are brought into action. But here their analogy ceases.

Vegetables, we know, require a particular temperature, season, soil and aspect, for their growth and maturity, and, in many instances, even for their very existence. In cold climates, they are, in consequence, proportionably limited in the number of their species; and, in the winter, even of temperate regions, many of their functions are suspended; they cease to grow, they part with one of their most essential organs, their leaves, and they require the return of a more congenial season, before their variously animating powers are again roused into action. Animals, on the contrary, so long as the vital principle be continued, ‘preserve their various functions in full activity and similitude, in whatever temperature, season, soil, or aspect, they may be placed ; and a loss of any of their important organs, or a considerable interruption to the functions of the others, very frequently terminates in their general dissolution.

Vegetables, again, have not a brain and nervous system to endow them with perceptive powers, or, as far as we can judge, with sensation; nor muscles to promote their locomotion, so necessary to most animals which are to make choice of their food, and whose means of supply are not confined to a narrow circle as in vegetables, in which nature by their peculiar mechanism, has bestowed on them the means of obtaining their nourishment from the soil which first gave them birth. For this purpose the latter are permanently fixed to one spot in the earth, and the vital spark having once been excited, their different movements are rendered dependent upon principles, in which the will has no concern, and where perception cannot be required.

These reflections necessarily lead us to a consideration of the structure and functions of vegetables, in which the analogy of the two kingdoms will be further illustrated, and of the line of distinction, we hope, satisfactorily explained.

To consider vegetable physiology in all its relative bearings, it will be requisite to divide the subject into four distinct heads. First, the structure and functions of those parts of a vegetable which contribute to its nourishment and preservation, including the root, trunk, branches and leaves. Secondly, of those organs which are necessary to its reproduction, and these have reference to the flower, fruit and seed. ‘Thirdly, the process of generation and germination, of the food and agents effecting its growth, and the formation and completion of a new plant. And lastly, the casualties affecting the life of vegetables, consisting of wounds, diseases, natural decay and renovation.

But previously to entering into a particular description of the several organs, it will be proper to observe that vegetables, like animals, are composed of fluids and solids. The fluid parts produce those which are solid; and the only aliment which effects and preserves plants, being in a liquid or aereform state, it_is wonderfully contrived that there should be an organic vascular system for its distribution, and that it should likewise possess the vital power of assimilation, in order to effect and perpetuate the growth which takes place, and to diversify the products which characterize the innumerable variety of plants which constitute the vegetable kingdom.

GeneRAaL Texture oF PuantTs.

Much light has been thrown upon the general texture of vegetables, by the microscopic figures of Grew, Malpighi and others, but more especially the observations and highly magnified dissections of M. Mirbel. From preceding writers we have learned the general tubular or vascular structure of the vegetable body, and the existence of some peculiar spirally-coated vessels in many plants. On these slender foundations physiologists have, at their pleasure, constructed various theories, relative to the motion of the sap, respiration and other functions, presumed to be analogous to those of animals. The anatomical observations of Mirbel go further than those of Grew, &c., and it is necessary to give a short account of his discoveries.

He finds, by the help of the highest magnifying powers, that the vegetable body is a continued mass of tubes and cells; the former extend indefinitely, the latter frequently and regularly interrupted by transverse partitions. ‘These ‘partitions being in the corresponding cells, and each cell increasing somewhat in diameter after its first formation, except when restrained by the transverse partition, seems to account for the hexagonal figure.* The membraneous sides of all these cells and tubes are very thin, more or less transparent, often porous, variously perforated or torn. Of the tubes, some are without any lateral perforations, at least for a considerable extent; others pierced with holes ranged in a close spiral line; in others several of these holes run together, as it were, into interrupted spiral clefts; and in some,

——— een *-For illustrations of this part of the subject, see Plate I.

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* those clefts are continued, so that the whole iube, more or less, is cut into a spiral line; which, in some young branches and tender leaves, will unroll to a great extent, when they are gently torn asunder. The cellular texture especially is “extended to every part of the vegetable body, even into the thin skin, called the epidermis, which covers every external part, and into the fine hairs or down which, in some instances, clothe the cuticle itself. Before we offer any thing upon the supposed functions of these different organs, we shall take a general view of the vegetable body, beginning with the root, the first organ to be described.

CHAP. I. ANATOMY OF THE Root

The root, which, though often differing in its bulk and shape, is similar in all its structure and use, (with the exception of the bulb, which, from containing the rudiments of a new individual, may more properly be considered a variety of the seed,) is that part of the vegetable which fixes the plant to the ground, is its organ of nourishment, and the apparatus by which, through its various ramifications, below the surface, it imbibes food from the soil.

In its structure, it is composed of the same parts as the stem and branches, and therefore may only be considered as the stem inverted ; the lower portion of the tube dipping into the earth, and forming itself into minute ramifications without leaves ; and the upper portion ascending, and producing buds, branches and leaves. ‘This has been illustrated by experiments made upon the plum, cherry and willow, in which, by inverting the stem and root, the former has become a root, sending out ramifications, and the latter a stem producing leaves, flowers and fruit. The sffucture of the root and stem is therefore one and the same thing, and it is the situation in which each is placed, and the operation of the surrounding medium, that makes the difference ; giving to each, a variation in its chemical and medicinal properties though their physical structure continue the same.

The main body of the root, which has been termed the caudew, upon its first penetrating the ground, possesses but very limited powers of affording nourishment; and it is not until it has sent forth its ramifications or radicule, and these ramifications have issued sti!l finer filaments of capillary diameter, that an extensive absorption can be eff cted. ‘These minute tubes, by dipping into the soil in the direction where there is the least opposition, abstract from it, by some undiscovered process, those nutritive parts, which, through the agency of water, become sap, and convey it to the caudex, from whence it rapidly ascends to the stem and branches, and thence to the uttermost extremity of the leaves, there to undergo a new modification to be hereafter explained. ‘The root therefore may be considered as acting the same part towards the vegetable, as the stomach does to the animal; though the apparatus and the fluid prepared, bear but little similarity.

Or tHe Trunk or STEM.

In cutting the trunk of a tree from the circumference to the centre, the instrument passes through seven distinct parts, in the following order :

_ 1. The epidermis, which extends over the surface of every vegetable, as before described. It is also called cuticle, false skin and the like, names which anatomists have given to the external covering of animals. ‘There is a striking analogy between the animal and vegetable cuticle or skin. In the former it varies in thickness from the delicate film which covers the eye, to the hard skin of the hand or foot, the coarser covering of the ox, or the hard shell of the tortoise. In the latter it is exquisitively delicate, as in the covering of a rose leaf, and hard and coarse in the rugged coats of the elm and oak. In the birch, you may see the cuticle peeling off in circular pieces. The vital principle seems wanting in it; this is the only part of a living plant which is dead. In the larger trees and shrubs, the bodies of which, in themselves, are strong and of firm texture, the latter property is not of so much importance ; but in the reeds, the grasses, the canes with hollow stalks, and in the various farrinaceous seeds, where it is most essential that their structure should be protected from the action of insects ; nature, to render it more strong and resisting, has given it »ghsy Hd of net-work, composed principally of a silicious earth, which Sir H. Davy has ascertained in many instance capable of striking fire upon the application of the steel. :

2. The cellular integument, which lies immediately under the cuticle, and is for the most part of a green color, at least in the leaves and branches. ‘This is in general the seat of color, and in that respect analogous to the rete mucosum, or pulpy substance situated under the human cuticle, which is pale in the European, black in the Negro, and red in the American; but we must carry the analogy no further, for these two parts perform no functions in common. Du Hamel supposed this pulp to form the cuticle ; but this is improbable, as his experiments show, when that membrane is removed, that the cellular integument exfoliates, at least in trees, or is thrown off in consequence of the injury it has sustained, and a new cuticle, covering a new layer of the same succulent matter, is formed under the old one. Annual stems or branches have not the same power, any more than leaves.

Mirbel remarks that “leaves consist almost entirely of a plate of this substance, covered on each side by the cuticle. The stems and branches of both annual and perennial plants are invested with it; but in woody parts it is dried up and reproduced continually, such parts only having that reproductive power. The old layers remain, are pushed outward by the new ones, and form at length the rugged, dry, dead covering of the old trunks of trees.”

The petals of flowers are almost entirely composed of cellular texture, the cells of which are filled with juices fitted to refract and reflect the rays of light, so as to produce the brilliant and delicate tints which constitute so great a portion of their beauty.

3. The cortex or true bark of the plant, known to every one by the name of bark. It consists of but one layer in plants and branches only one year old, and often not distinguished from rt oe the wood, In the older branches and trunks of trees, it consists of as*many layers as they are years old.

The bark contains a great number of woody fibres, running for the most part longitudinally, which give it tenacity, and in which it differs very essentially from the other parts. ‘These woody fibres when separated by maceration, exhibit in general a kind of net-work, and in many instances great regularity and beauty of structure.

In the bark the peculiar virtues or qualites of particular plants chiefly reside, and more especially in several of its internal layers nearest to the wood. Here we find in appropriate vessels the resin of the fir and juniper, the astringent principle of the oak and willow, on which their tanning property depends, the fine and valuable bitter of the Peruvian bark, and the exquisitively aromatic oil of the cinnamon. The same secretions do indeed, more or less, pervade the wood and other parts of these plants, but usually in a less concentrated form.

4, The liber, which is the inner layer of the cortex or bark. It consists of lamine or plates, bound together by a cellular matter, which, when dissolved by maceration in water, detaches these plates or coatings from each other; when they resemble the leaves of the books of the ancients; whence arose the name of liber. ‘The liber is softer and more juicy than the cortex.

It is in this layer only that the essential vital functions are carried on; after a while it is pushed outward with the cellular integument, by the successive formation of new layers, and with the cellular integument finally becomes a lifeless crust. Grew, Malpighi, Du Hamel and others, supposed that the libe» annually changes, by hardening, into the alburnum or young wood, an opinion also maintained by Mirbel, and some of the ablest philologists, but which is founded upon mistaken principles. It is through the liber, however, that the matter in which the new wood is formed, which annually augments the diameter of the trunk and branches, is secreted ; and hence the importance of this portion of the bark.

As the net work formed by the dividing threads of the meshes is not readily dissolved in water, while the cellular matter which

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VEGETABLE PHYSIOLOGY. Li fills them up is remarkably soluble, the liber of some plants, as the Lace tree, (Daphne Lagetto), when soaked in water and afterwards beaten, forms a very beautiful vegetable gauze ; which may be used as an article of dress. A coarse. specimen of this gauze, or lace, is seen in the bark of many of our indigenous trees, particularly the oak, when it has been long exposed to the weather, after being separated from the trunk. The natives of Otaheite manufacture garments from the liber of the mulberry. The liber of flax is by a more refined process converted into linen. This regular arrangement, however, of the longitudinal texture of the liber is not found in every instance ; for on the fir and some other trees, the longitudinal threads are seen lying nearly parallel to one another, without any meshes or intervening cellular matter.

This part of the bark is important to the life of vegetables ; the outer bark may be peeled off without injury to them, but the destruction of the liber is generally fatal. The Operation of girdling trees, which is often practised in new countries, consists, in making with an axe, one or more complete circles through the outer bark and the liber of the trunk. Trees seldom survive this operation, especially if it has been performed early in the spring, before the first flow of the sap from the root towards the extremities.

5. The alburnum, or sap wood, which may be considered the grand vascular organ of the plant, which is made up of cells and tubular vessels; the cells being constantly filled with the rising sap, which, after undergoing some changes, is taken up by the tubes and conveyed to the leaves to their utmost extremity ; and having from them received a new modification, the sap is returned by the cortical vessels back to the trunk, and thence to the minutest filaments of the roots.

The alburnum is at first soft and vascular; but it afterwards becomes hard, and in some trees, is of a density almost equal to ion. While in the soft state, it is endowed with nearly as much irritability as the liber, and performs functions of great importance in the vegetable system; but when hardened, these functions

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cease, and in time it loses even its vitality ; not unfrequently decaying in the centre of the trunks of trees; which, often, still flourish, and put out new shoots as if no such decay existed. To carry on, therefore, the functions of the wood, a new circle of it is annually formed over the old; and thus, also, the diameter of the trunk and branches present, by the number of these annual zones, a pretty correct register of their age, each zone marking one year in the life of the part. The hardness of these zones of wood increases with the age of the tree, being most dense in the centre, and less and less hard as they approach the circumference. °

Various opinions have been entertained respecting the origin of the alburnum. Mr. Knight, however, by various experiments, has satisfactorily proved that it is formed from the secretion deposited by the vessels of the liber, but that it is not, as had been supposed by Du Hamel, Dr. Hope and Mirbel, a transmutation of the liber itself.

Mr. Knight is of opinion, that the bark deposits the alburnous matter; but that the leaves are the organs in which this matter is elaborated from the sap; or, that the alburnum is generated from the cambium of Grew, which is part of the proper juice of the plant, formed by the exposure of the sap to the light and air in the leaf, and returned from it by the vessels that pass down from the leaf into the interior bark, by which it is deposited, and we may add, elaborated by the action of the vital principle inherent in this part of the plant. ‘To determine this point, he removed narrow circles of bark from roots of apple trees, “ leaving a leaf between the places where the bark was taken off; and on examining them frequently during the autumn,” he found that the diameter of the shoot between the insertion of the leaf stalk and the lower incision, was as much increased as in any other part of the tree ; but when no leaf was left ‘on similar portions of insulated bark, on other branches of the same age, no apparent increase in the size of the wood was discoverable.”

These experiments explain the reason why trees and shrubs having their Jeaves destroyed by caterpillars form scarcely any new wood in. that season; and, indeed, every one who has a pruned a tree, or shortened a growing twig, must have observed that the part above the last leaf always shrivels and dies, while all below it continues to live and increase in diameter.

6. The lignum, or heart wood, which, when present, is seated below the alburnum, seems principally intended, (like the bones of animals,) to give solidity, form and support to the more solid parts of the plant, and is mostly observable in old trees.

Substantial as is the wood or ligneous part of a tree, it is nevertheless so far from being an essential part, that many plants are without it. The arundaceous plants, as the reeds and the grasses, and, indeed, all the gramina, are naturally hollow.

7. The medulla, or pith, which is a soft and spongy, but often succulent substance, occupying the centre of the root, stem and branches, and extending in the direction of their longitudinal axes, in which it is inclosed as in a tube. In its structure it is exactly similar to that of the cellular tissue of the bark; being composed of an assemblage of cells, containing a watery and colorless fluid. Its form is regulated by that of the cavity it fills, which in the majority of instances is nearly circular ; but to this there are many exceptions. Thus in the horizontal section of a young stem of the elder (Sambucus) and the plane (Platanus), we find it circular, but furrowed by the bundles of the spiral vessels of the part that surrounds it. In the ivy and ash itis oval; irregularly oval and furrowed in the plane ; triangular in the oleander (Nerium Oleander) ; pentangular in the European oak (Quercus Robur) ; four-sided, with the angles obtuse, or tetragonal, in the common lilac, and yellow-flowering horse chesnut (sculus Flava); and pentagonal in the walnut (Juglans regia). But besides the diversities of form which the pith presents, it varies in diameter in other respects. In the young tree, of a few inches in height, it is smallest at the basis of the stem, largest in the middle, and smaller again at the summit ; and in the growth of each future year, nearly the same variations in its diameter are observable. In trees more advanced, pressed and acted upon by the heart wood, it begins to diminish ; and in very old trées it disappears altogether.

Linnzus attributes great importance to the pith, and erroneously asserts, after Bradley, that it gives birth tothe buds. Some botanists of the first rank believe, that the pith is, in a plant, what the brain and spinal marrow are in the inferior order of animals. “The pith,” says Darwin, “‘ appears to be the first or most essential rudiments of the new plant, like the brain, spinal marrow, and medulla oblongata, which is the first visible part of the figure of every animal foetus from the tadpole to mankind.” It seems, however, that the pith is not essential, or absolutely necessary to vegetation, as we often observe trees to live and thrive without it. The guaiacum or lignum vite, it is said has no pith. Most naturalists, however, consider the pith only of secondary importance; though they allow its use in making good the nutritive exhaustion which the rapid growth of young shoots never fails to produce.

Or tHe Bups.

No part of the vegetable structure has been examined with. more accuracy than that of buds, (Gemme), from the time of the faithful and diligent Grew, to that of the discriminating and candid Knight, and yet it is very singular that little was known of their physiology until the experiments and observations of the last gentleman were made public. ‘To him, therefore, we are indebted for some of our most valuable knowledge on this subject.

A bud is that part which contains the rudiments of a plant, o of a part of a plant, for a while in a latent state, till the time of the year, and other circumstances, favor their evolution. From buds, then, an entire plant. may be produced, if placed in favorable circumstances, or only a branch, or leaves, or flowers. We can, however, reckon no more than two kinds, those that produce leaves, and those that produce flowers. There is the closest analogy between these organs and bulbs; so close, indeed, that Mirbel, and some others, arrange them together. Practical cultivators mark distinct characters peculiar to each kind of bud. ‘Those that produce leaves are small, long and pointed ; the flower buds, again, are thick, short and round. It appears probable that some unknown agents influence the

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VEGETABLE PHYSIOLOGY. QI formation either of flower buds or of leaf buds, or rather that some circumstances will cause the evolution of either of them from the same bud. A fact recorded in the Linnean Transactions in some measure favors this opinion. The Solandra grandiflora, a native of Jamaica, had been long cultivated in the English stoves, and propagated by means of cuttings ; but none of the plants ever displayed any signs of fructification. They had been always well supplied with water. One plant, by accident, was left without being watered in the dry stove at Kew: the consequence was, that the branches were much stunted in their growth, and flowers were produced. The experiment has been frequently repeated with success. It appears, that whatever checks the luxuriance of the leaves, tends to the formation of flowers and seeds.

For the purpose of converting leaf buds into flower buds, various expedients may be used with advantage : such as scoring _ the bark to the wood very deeply with a knife, twisting a wire tightly round the stem, or by cutting off a cylinder of the bark, and replacing it with a bandage.

It is said that there is an jntermediate species of bud, which retains some of the characters of each. A striking difference has been noted between the leaf and the flower buds ; the first may be removed with impunity from its original situation, and placed in the earth, where it will vegetate with luxuriance ; but the last uniformly dies. Both may be removed to another stock with success. This operation is called budding, or inoculation, and is well known to gardeners. Each bud may be considered a distinct being, containing parts precisely similar to those of the parent tree, which, when favorably situated, will develope themselves, and form a plant retaining all the peculiarities of the parent. If those qualities are such as will constitute a variety, they will also be perpetuated; and of this, we have many familiar examples in the various fruit trees commonly cultivated in our gardens, on many of which, budding is the only means of procuring good fruit. The branch formed by the inoculated bud alone yields proper fruit; nor is the stock, on which the budding has been performed, in the least degree altered. The crab, on which the finest apple has been budded, still remains a crab: thus proving, that it serves merely as a source from which the young bud derives its nourishing matter ; 5% although it is highly probable, from the difference of the results, that, that matter undergoes some peculiar elaboration, after leaving the vessels of the original stock. On this principle, five or six different species of fruit have been known to be budded on the same tree, and which, in full fruit, exhibited a singular and beautiful spectacle. It is impossible to say how a bud torn from one tree,.and put in the place of another bud in another tree, should become a perfect branch, producing flowers and fruit in the highest perfection; but attempts have been made to trace the various steps of nature in effecting her operations. Accordingly it is said, that after the fresh bud has been inserted into the wound, formed by the extraction of another bud, that the cambium unites the two parts, forms a connecting medium for the vessels of the bud and the tree, and thus enables the vegetative process to go on whenever nature requires it. Mr. Knight has noticed some facts worthy of record; and he states that ‘a line of confused organization marks the place where the inserted bud first comes into contact with the wood of the stock, between which line and the bark of the inserted bud, new wood, regularly organized, is generated. ‘This wood possesses all the characteristics of that from which the bud is taken, without any apparent mixture with the character of the stock in which it is inserted. ‘The substance which is called the medullary process, is clearly seen to spring from the bark, and to terminate at the line of its first union with the stock.”

The usual position of buds is in the axil of the leaves, except in the genera Mimosa, Gleditschia and a few others. The buds are opposite to each other when the branches or leaves are opposite, alternate when the latter are alternate, and terminal when the leaves are terminal. In those plants that have both opposite and alternate leaves or branches, the buds are commonly solitary.