« PreviousContinue »
collects it while on the wing, fluttering from flower to flower, and all the while humming its simple accent of pleasure. Its tongue, like that of many insects, is missile. When taken it expires instantly; and after death, on account of its diminutive size, the elegance of its shape, and the beauty of its plumage, it is worn by the Indian ladies as an ear-ring. This species, however, in truth, has no physiological relation with insects. It is only in its diminutive size that it makes an approach to the larger species of arachnida.
Such being the perplexity and seeming confusion that extend through the whole chain of animal life, it is not to be wondered at that we should at times meet with a similar embarrassment in distinguishing between animal life and plants, and between plants and minerals. I gave a cursory glance at this subject in our last lecture, and especially in regard to that extraordinary division of organised substances which, for want of a better term, we continue to denominate zoophytes; many of which, as, for example, various species of the alcyony and madrepore, bear a striking resemblance to crystals and other mineral concretions; while great numbers of them, and particularly the corals, corallines, and some other species of alcyony, as the sea-fig, sea-quince, puddingweed, and above all the stone-lily (which last, however, is now only found in a petrified state), have the nearest possible approach to a vegetable appearance. Whence, as I have already observed, amongst the earlier naturalists, who expressly directed their attention to these substances, some regarded them as minerals, and others as vegetables; and it is not till of late years, only, indeed, since it has been
ascertained that the chemical elements they give forth on decomposition are of an animal nature, that they have been admitted into the animal kingdom.
Among plants, in like manner, we often meet with instances of individual species that are equally doubtful, not only as to what kind, order, or class of vegetable existence they belong, but even as to their being of a vegetable nature of any kind, till their growth, their habits, and their composition are minutely examined into. But, independently of these individual cases, we also perceive, in the general principle of action in animal life, that, the more it is investigated, the more it is calculated to excite our astonishment, and to indicate to us, so far as relates to the SUBORDINATE POWERS of the animal frame, the application of one common system to both, and to demonstrate one common derivation, from one common and Almighty Cause. Having, therefore, in our last lecture, submitted to your attention a brief outline of the structure of plants, I shall now proceed to point out a few of these general resemblances, and shall endeavour to select those which are either most curious or most prominent.*
Plants, then, like animals, are produced by ordinary generation; and though we meet with various instances of production by the generation of buds and bulbs, or of slips and offsets, the parallelism, instead of being hereby diminished, is only drawn the closer; for we meet with just as many instances of the same varieties of propagation among animals. Thus, the hydra, or polype, as it is more generally
* Consult also Mr. Knight's article, Phil. Trans. 1810, part ii. p. 179-181.
called, the asterias, and several species of the leech, as the hirudo viridis, for example, are uniformly propagated by lateral sections, or pullulating slips or offsets *; while almost every genus of zoophytic worms is only capable of increase by buds, bulbs, or layers; and some of these animals, like the houseleek and various grasses, by spontaneous separation. In effect, most of the kinds now referred to, whether animals or vegetables, may be regarded less as single individuals than as assemblages or congeries of individuals; for in most of them every part exists distinctly of every other part, and is often a miniature of the general form. The various branches of a tree offer a similar example, and present a striking contrast with the various branches of a perfect animal. In the latter, every distinct part contributes to one perfect whole: the arm of a man has no heart, no lungs, no stomach; but the branch of a tree has a complete system of organs to itself, and is hence capable in many cases of existing by itself, and producing buds, layers, and other kinds of offspring, when separated from the trunk. The different parts of the polype are equally independent, and are hence equally capable of a separate increase. It is owing to this principle that we are able to graft and bud: and M. Trembly having applied the same kind of operation to the animals we are now
Thus Aristotle, upon a subject which is generally supposed to be of modern discovery, Ωσπερ γὰρ τὰ φυτὰ καὶ ταὐτὰ (scilicet) ἔντομα διαιρούμενα δύναται ζῇν. "For, like plants, such insects also maintain life after slips or cuttings." Hist. Anim. lib. iv. ch. 8.
See a variety of other curious instances in the author's translation of Lucretius, note to b. ii. ver. 880.
speaking of, found that, by numerous grafts of different kinds upon each other, he was enabled to produce monsters as wild and extravagant as the most visionary poet or fabulist ever dreamed of.
The blood of plants, like that of animals, instead of being simple, is compound, and consists of a great multitude of compacter corpuscles, globules for the most part, but not always globules, floating in a looser and almost diaphanous fluid. From this common current of vitality, plants, like animals, secrete a variety of substances of different and frequently of opposite powers and qualities, substances nutritive, medicinal, or destructive.
And, as in animal life, so also in vegetable, it is often observed that the very same tribe, or even individual, that in some of its organs secretes a wholesome aliment, in other organs secretes a deadly poison. As the viper pours into the reservoir situated at the bottom of his hollow tusk a fluid fatal to other animals, while in the general substance of his body he offers us not only a healthful nutriment, but, in some sort, an antidote for the venom of his jaw so the jatropha manihot, or Indian cassava, secretes a juice or oil extremely poisonous in its root, while its leaves are regarded as a common esculent in the country, and are eaten like spinachleaves among ourselves; though the root, when deprived, by exposure to heat, of this poisonous and volatile oil, is one of the most valuable foods in the world, and gives bread to the natives, and tapioca as an article of commerce. Its starch is like that of the finest wheat-flour, and, combined with potatoes and sugar, yields a very excellent cider and perry, according to the proportions em
ployed. In like manner, while the bark of the cinnamon tree (laurus cinnamomum) is exquisitely fragrant, the smell of the flowers is highly offensive, and by most persons is compared to that of newlysawn bones, by St. Pierre to that of human excrement.* So the cascarilla bark and castor oil are obtained from plants poisonous in some part or other.
The amyris, in one of its species, offers the balm of Gilead tree; in another, the gum-elemi tree; and in a third, the poison-ash, that secretes a liquid gum as black as ink. It is from a fourth species of this genus, I will just observe, as I pass along, in order the more completely to familiarise it to us, that we obtain that beautiful plant which, under the name of rosewood‡, is now so great a favourite in our drawing-rooms.
The acacia nilotica §, or gum-arabic tree, is a rich instance in proof of the same observation. Its root throws forth a fluid that smells as offensively as asafoetida; the juice of its stem is severely sour and astringent; the secernents of its cutis exude a sweet, saccharine, nutritive gum, the common gumarabic of the shops, and its flowers diffuse a highly fragrant and regaling odour. So the arenga palm produces sugar, an excellent sago, and a poisonous juice that even irritates the skin.
But perhaps the laurus, as a genus, offers us the most extensive variety of substances of different qualities. This elegant plant, in one of its species,
* Mr. Marshall's account delivered to the Royal Society. See Thomson's Annals, Sept. p. 242.
+ A. toxifera.
+ A. balsamifera.