An introduction to physiological and systematical botany/Chapter 1
PHYSIOLOGICAL AND SYSTEMATICAL
DISTINCTIONS BETWEEN ANIMALS, VEGETABLES AND FOSSILS.—ON THE VITAL PRINCIPLE ESSENTIAL TO THE TWO FORMER.
Those who with a philosophical eye have contemplated the productions of Nature, have all, by common consent, divided them into three great classes, called the Animal, the Vegetable, and the Mineral or Fossil Kingdoms. These terms are still in general use, and the most superficial observer must be struck with their propriety. The application of them seems at first sight perfectly easy, and in general it is so. Difficulties occur to those only who look very deeply into the subject.
Animals have an organized structure which regularly unfolds itself, and is nourished and supported by air and food; they consequently possess life, and are subject to death; they are moreover endowed with sensation and with spontaneous, as well as voluntary, motion.
Vegetables are organized, supported by air and food, endowed with life and subject to death as well as animals. They have in some instances spontaneous, though we know not that they have voluntary, motion. They are sensible to the action of nourishment, air, and light, and either thrive or languish according to the wholesome or hurtful application of these stimulants. This is evident to all who have ever seen a plant growing in a climate, soil, or situation, not suitable to it. Those who have ever gathered a rose, know but too well how soon it withers; and the familiar application of its fate to that of human life and beauty, is not more striking to the imagination than philosophically and literally true. The sensitive plant is a more astonishing example of the capability of vegetables to be acted upon as living bodies. Other instances of the same kind we shall hereafter have occasion to mention.
The spontaneous movements of plants are almost as readily to be observed as their living principle. The general direction of their branches, and especially of the upper surface of their leaves, though repeatedly disturbed, to the light; the unfolding and closing of their flowers at stated times, or according to favourable or unfavourable circumstances, with some still more curious particulars to be explained in the sequel of this work, are actions undoubtedly depending on their vital principle, and are performed with the greater facility in proportion as that principle is in its greatest vigour. Hence arises a question whether Vegetables are endowed with sensation. As they possess life, irritability and motion, spontaneously directing their organs to what is natural and beneficial to them, and flourishing according to their success in satisfying their wants, may not the exercise of their vital functions be attended with some degree of sensation, however low, and some consequent share of happiness? Such a supposition accords with all the best ideas we can form of the Divine Creator; nor could the consequent uneasiness which plants must suffer, no doubt in a very low degree likewise, from the depredations of animals, bear any comparison with their enjoyment on the whole. However this may be, the want of sensation is most certainly not to be proved with regard to Vegetables, and therefore of no use as a practical means of distinguishing them, in doubtful cases, from Animals.
Some philosophers have made a locomotive power peculiarly characteristic of Animals, not being aware of the true nature of those half-animated beings called Corals and Corallines, which are fixed, as immoveably as any plants, to the bottom of the sea, while indeed many living vegetables swim around them, unattached to the soil, and nourished by the water in which they float. Some have characterized Animals as nourished by their internal, and Vegetables by their external surface, the latter having no such thing as an internal stomach. This is ingenious and tolerably correct; but the proofs of it must fail with respect to those minute and simply-constructed animals the Polypes, and the lower tribes of Worms, whose feelers, put forth into the water, seem scarcely different from roots seeking their food in the earth, and some of which may be turned inside out, like a glove, without any disturbance of their ordinary functions. The most satisfactory remark I have for a long time met with on this difficult subject is that of M. Mirbel, in his Traité d'Anatomie et de Physiologie Végétables, a work I shall often have occasion to quote. He observes, vol. I. p. 19, "that plants alone, have a power of deriving nourishment, though not indeed exclusively, from inorganic matter, mere earths, salts or airs, substances certainly incapable of serving as food for any animals, the latter only feeding on what is or has been organized matter, either of a vegetable or animal nature. So that it should seem to be the office of vegetable life alone to transform dead matter into organized living bodies." This idea appears to me so just, that I have in vain sought for any exception to it.
Let us however descend from these philosophical speculations to purposes of practical utility. It is sufficient for the young student of Natural History to know, that in every case in which he can be in doubt whether he has found a plant or one of the lower orders of animals, the simple experiment of burning will decide the question. The smell of a burnt bone, coralline, or other animal substance, is so peculiar that it can never be mistaken, nor does any known vegetable give out the same odour.
The Mineral Kingdom can never be confounded with the other two. Fossils are masses of mere dead unorganized matter, subject to the laws of chemistry alone; growing indeed, or increasing by the mechanical addition of extraneous substances, or by the laws of chemical attraction, but not fed by nourishment taken into an organized structure. Their curious crystallization bears some resemblance to organization, but performs none of its functions, nor is any thing like a vital principle to be found in this department of Nature.
If it be asked what is this vital principle, so essential to animals and vegetables, but of which fossils are destitute, we must own our complete ignorance. We know it, as we know its Omnipotent Author, by its effects.
Perhaps in the fossil kingdom heat may be equivalent to a vital principle; but heat is not the vital principle of organized bodies, though probably a consequence of that principle.
Living bodies of animals and plants produce heat; and this phænomenon has not, I think, been entirely explained on any chemical principles, though in fossils the production of heat is in most cases tolerably well accounted for. In animals it seems to have the closest possible connexion with the vital energy. But the effects of this vital energy are still more stupendous in the operations constantly going on in every organized body, from our own elaborate frame to the humblest moss or fungus. Those different fluids, so fine and transparent, separated from each other by membranes as fine, which compose the eye, all retain their proper situations (though each fluid individually is perpetually removed and renewed) for sixty, eighty, or a hundred years, or more, while life remains. So do the infinitely small vessels of an almost invisible insect, the fine and pellucid tubes of a plant, all hold their destined fluids, conveying or changing them according to fixed laws, but never permitting them to run into confusion, so long as the vital principle animates their various forms. But no sooner does death happen, than, without any alteration of structure, any apparent change in their material configuration, all is reversed. The eye loses its form and brightness; its membranes let go their contents, which mix in confusion, and thenceforth yield to the laws of chemistry alone. Just so it happens, sooner or later, to the other parts of the animal as well as vegetable frame. Chemical changes, putrefaction and destruction, immediately follow the total privation of life, the importance of which becomes instantly evident when it is no more. I humbly conceive therefore, that if the human understanding can, in any case, flatter itself with obtaining, in the natural world, a glimpse of the immediate agency of the Deity, it is in the contemplation of this vital principle, which seems independent of material organization, and an impulse of his own divine energy.