the materials necessary to its existence. These changes are truly caused by a digestive process of which we know exceedingly little. We well know, however, some of its marked results; fluids taken up in an insipid and inodorous state, are returned, strongly possessed of sapidity, odour, acrimony; or holding large quantities of saline and other matters in solution. Whatever the power may be that governs these changes, it is not inherent in any especial part at present understood by us; or, at least it is not proved that any position is absolutely necessary to the correct action of the organs. This may be readily proved, by the frequently repeated experiment of placing vegetable bodies in the most unnatural positions. Thus, trees may be dug up, their branches be cut off, and these ends of branches be placed in the earth, with the roots in the air, completely reversing the order of nature; yet in a short time, what were lately roots begin to bud, and are eventually covered with foliage, while the branches set in earth, gradually send forth radicles, and ultimately assume the characters and offices of roots; proving that the digestion of vegetables takes place as well when the tubes are placed in one direction as another. This experiment was once performed on an extensive scale, by a citizen of Philadelphia, who caused a row of willows to be thus inverted, to the great surprise of his neighbours. These trees soon resumed their ordinary appear ance. The lowest degree of animation, is that exhibited by vegetables, whose organization, though necessarily various in different orders, genera and species, may nevertheless be stated in general terms to consist of a series of capillary tubes, contained within a bark or rind, and endowed with a peculiar degree of vitality, as is rendered evident by the elevation of fluids far above the level to which they could be raised by mere atmospheric pressure; by the formation of numerous products, such as gums, resins, sugar, &c.; and by the healing of wounds made through their integument or bark. In addition to their growth, flowering and fructification, vegetables exhibit curious and interesting phenomena, showing various degrces of susceptibility to the influence of light, heat, and other agents; being in this respect analogous to the higher ranks of animated nature, in their ability to respond to the impressions of stimulants, by an increase of the motions of their fluids, and an augmentation of energy in all their functions. On this susceptibility is founded some share of the success with which the agriculturist applies himself to the melioration of soils, by the addition of plaster of Paris and various other agents. Besides the simple property of irritability, vegetables are capable of certain kinds of self-motion. Certain plants expand their leaves during the day, and close them towards nightfall; others remain closed during the day, and unfold only at night. Mo tions of this sort may be explained by the changes which variations of temperature induce in the current of fluids passing through such vegetables. Yet some vegetables move in a very different manner, gathering up their leaves, and, finally, withdrawing the whole foot-stalk from the touch, as is seen in the sensitive plant: this might be attributed to the temperature of the hand or finger applied, were it not that the same movement occurs when the touch is from any substance, without reference to temperature. Hence, we are forced to admit that the term sensitive is correctly applied, and that these plants do feel, beyond the action caused by slight variations of temperature. If stronger evidence be required, we have it in the plant which grows in Florida, known by the name of Venus's fly-trap, the dionea muscipula. The leaves of this plant are composed of two lobes, which lie, under ordinary circumstances, horizontally expanded; but when a worm, fly, or other insect, gets on these leaves, the lobes rise up, and become compressed against each other, so as to catch and retain the aggressor. The evidence of an extreme degree of sensibility is presented in this plant, which is capable of feeling the movements of an insect, which might scarcely be felt upon the skin of a more perfect being. A peculiar motion is also performed by vegetables, in the turning of the superior surfaces of their leaves towards the light, even where pains have been taken to prevent or render it difficult. Notwithstanding these circumstances, no one has yet been. able to discover in vegetables organs of sense and motion analagous to those of other portions of animated nature, although the anatomy of plants has received a very considerable share of attention. A vast number of facts similar to those related might be collected from the vegetable kingdom, to show, that however low they may stand in the scale, they are in many respects constructed like creatures of a higher order; and that for some of them we might claim something beyond mere irritability, though we can scarcely feel authorized to conclude, as naturalists have done, that they are capable of volition. We have every reason to believe that the simplest of vegetable growths formed the first covering of the earth, inasmuch as they can derive sustenance from soils incapable of supporting larger vegetables. Myriads of such productions growing and perishing in succession, formed, with earthy matters, the commencement of a soil for larger and more lasting growths; preparing an inexhaustible supply of food for other, and more perfect, animated beings. In the vegetable world we have no plants directly sustained by the destruction of others, although all are indirectly thus supported. Vegetables do not prey upon each other; yet have they their modes of co-operating in the great work of destruction. They increase and multiply in such profusion as to destroy the weaker, either by the number and strength of their roots forcing the weaker out of the soil; or by their tangled and umbrageous canopies of branches, excluding the influence of the sun and dew from plants which live only under the genial influence of sunshine and shower. In other instances, apparently insignificant vines shoot forth their green and curling tendrils, embracing every asperity and projection of neighbouring sycamores, oaks, or poplars, and, climbing to their topmost branches, spread out their own luxuriant foliage, in such weight and profusion as to smother the giant in his strength, and bear down his branching honours in fatal decay. In one mode, vegetables may be said to prey upon each other; there are a vast number of parasite plants, which, instead of being rooted in the soil, derive their nourishment from the surface of trees and shrubs to which they are attached. The seeds of these parasites, blown about by the wind, are wafted through forests and fields, and, becoming adherent to the bark of the tree, grow vigorously, though without inflicting any obvious injury. Persons who have journeyed through forests in winter, may have been surprised at the sight of a green bush flourishing amid the highest branches of a leafless oak; without being aware, at the moment, that this plant formed no part of the tree to which it was accidentally fastened. The sombre and melancholy effect produced on the traveller's feelings by the dense pine forests of our southern country, is greatly heightened by the long pendants of a mossy parasite, which, while the topmost branches of the trees are violently agitated by the winds, are merely swayed to and fro, like the heavy and mournful movements of a funeral pall. The vegetable kingdom exhibits some singular and interesting instances of reprisal upon animal life, besides those which have been noticed in the instance of the dionea muscipula. There are numerous plants of the, fungus kind, not less peculiar for their appearance than their odour, which is exactly similar to that of flesh in an advanced stage of putrefaction. Around one of these plants, in a warm day, may be seen hovering the carnivorous flies, as thickly as if it were really decaying animal matter. Their instinct, remarkable as it is, cannot prevent them from being deceived: they eagerly deposit their eggs in this apparently favourable bed-but they are doomed to destruction. The fungus which shot up during the moistness of one night, must be dried up by the warmth of the next day's sun, and with its exsiccation perishes the insect race committed to its cherishing. * The largest flower ever discovered belonged to a plant of this kind-the petals of the flower, when expanded, measuring a yard in diameter. See the Transactions of the Linnæan Society, vol. xiii. where it is described, and the genus named Rafflesia, after its discoverer, Sir Stamford Raffles. In the lowest orders of animal existence, we find motion to be the first perceptible attribute of life, as the creatures examined are too transparent to allow any difference of parts to be distinguished in their mass. The simplest form of animal existence is distinguished from the vegetable, by being provided with an especial cavity, into which the aliment is first received, and undergoes some change, before it is assimilated to the substance of the animal. In some of these creatures a sufficiently striking analogy is presented, to the inverted position of vegetables heretofore mentioned. The animals consisting of a body so formed as to constitute a simple sac or cavity, may be turned inside-out, and the outside surface, thus changed into the sac for receiving food, is capable of digesting it exactly as was done by the original internal surface. These lowest forms of animal existence resemble vegetables still more closely in their power of reproduction from slips, or cuttings from the trunk; each piece being capable of growing to a perfect animal, as each slip of a tree may grow to the size and vigour of the parent stem. The next step in the scale of organization, is that in which the organs of digestion are composed of a cavity for the reception of food, which is conveyed thereto from an orifice or mouth, through an appropriate tube, while the superfluous or excrementitious matters are conveyed away in an opposite direction. To these organs, as we ascend in the scale, we find gradual additions of other and more complicated structures, until we have them combined with a nervous or sentient system; a system of vessels for the circulation of fluids, and an apparatus for the inhalation of atmospheric air. As we rise from the lower to the higher orders, we observe a proportional perfection in the organs of sense; vast multitudes of the creatures of the lowest class, appear to possess no sense, unless it be that of touch, and even this in a very obscure degree. Sight is possessed by some, apparently destitute of other senses;-smelling, hearing, and tasting, are enjoyed in perfection only among the animals which approximate to the higher divisions. In proportion as the senses are perfectly developed and exercised, we find the other attributes of being advanced; nevertheless, the paramount excellence of any one sense is not attended by an especial degree of perfection in other qualities. The first rudiments of the sentient system discoverable in the lower classes, consist either in simple nervous filaments, arranged along the digestive canal, or a succession of small knotted masses, which are termed ganglia. Going upwards from these creatures to the superior classes, we find the simple chord changing to one of more marked and symmetrical character, and expanding at its anterior extremity, forming the commencement of a brain. This, in still more perfect animals, is developed more and more, from below, till in the most perfect of all animals, the posterior part, or that especially belonging to the animal motions, is entirely surpassed by a superior and anterior part, evidently destined to more exalted uses. This portion of the nervous system, the brain proper, has but slight and remote connexion with the organs of sense. All the nerves of sensation, with the solitary exception of the small pair belonging to the sense of smelling, arise from the back part and inferior surface of the lesser brain or cerebellum, and the mesial lobe or commissures joining the animal and intellectual parts of the nervous system. The origin, or attachment of the nerves of sense alone, is sufficient to convince us, that the forepart of the great organ within the skull is designed for some higher purpose than that of mere animal life; and the apparent exception of a single pair of nerves being attached to this anterior part, we do not believe to affect the correctness of the general rule. * The manner in which the nervous system is constructed and protected, has given rise to an excellent and useful division of the animal kingdom. In one grand division, this nervous system is either imperceptible or is disposed upon the surface of the digestive canal. In the other, the nervous system is protected by being enclosed by a peculiar bony case, formed of a succession of bones, which, though hollow, are jointed together so as to allow of various degrees of motion. These joints are called vertebræ ; hence the animals possessing them are called vertebral, while the first indicated creatures, being destitute of them, are called invertebral. The first division is the least numerous, and the best known; the second is so numerous as to defy comprehension or calculation of their number. The most curious complications of structure and function are found in vertebral animals; the most simple and singular modifications are to be seen in the invertebral. The vertebral exhibit the greatest number of analogies with the human body; the invertebral afford us the most ample means of illustrating peculiarities of individual organization. All are necessary to the full elucidation of the study of life, and all must be resorted to in the exploration of the sublime truths and admirable generalizations of philosophical anatomy-the ultimate object of all researches into the structure and actions of animals. In the first soil produced by vegetable decomposition commingled with earthy fragments, we find innumerable microscopic insects, whose business is still farther to complete decomposition, and their lives being extremely ephemeral, their own destruction aids in preparing nutriment for other forms of existence. To counterpoise the amazing reproductiveness of vegeta * In taking the liberty to speak thus of the brain, we are amply borne out by the fact, that the animal or intellectual character of all beings, is in direct propor tion to the comparative size and perfection of these two parts of the brain. |