To these colossi of the animal kingdom, we may oppose the colossi of the vegetable kingdom; the monstrous baobab gourd, which covers hundreds of square yards with its shade, the elm, whose trunk may grow to the size of a whale's girth, the Eucalyptus globulus, an Australian tree which is being acclimatized in Algeria and in the south of France, the Sequioœa gigantea, the giant of Californian forests.
If the two kingdoms of nature have their colossi, they have also their dwarfs, and their infinitely little. There are cryptogamic vegetables which are only to be seen with the microscope, and there are animalculæ equally invisible to the naked eye. If the animal kingdom can show, in its scale of size, the whale, and the microscopic acarus, the vegetable kingdom possesses a similar decreasing scale from the baobab to the lichens.
The same places are inhabited or resorted to by plants and animals. Both live on the same soil, as if for mutual aid. The two kingdoms combine at all points of the globe. We might name a number of places in which certain plants and certain animals thrive together. The chamois and the maple tree love the same mountains, the same high places; the truffle and the earth-worm dwell in the same underground region; the birch and the hare are found in the same place; the water-lily grows in the same fresh water with the aquatic worm; and the cod and the algæ prosper in the same submarine depths.
All vegetables and animals have an original country, but they can be acclimatized under other skies by human industry and skill. The chestnut-tree and the Indian cock, the peach-tree and the turkey, transported to Europe, has each forgotten its native land.
Among both animals and plants there are amphibious creatures. The frog, and the other batrachians, live, like the reeds, on the earth and in the water. Both animals and plants can live as parasites. The animal world has the flea, the louse, the acarus; the vegetable world has its lichens, and its mushrooms.
Thus, equal fecundity, similar variety in the scale of size, analogy in habitation, which implies ideality of organization, possibility of transplantation and of acclimatization out of their original country, possibility of amphibious existence, parasitical life, all general conditions which suppose a great analogy of organization; we establish all these things in drawing the parallel between plants and animals. How, then, if we grant sensibility to one of these kingdoms, can we deny it to the other?
6. Plants, like animals, have their maladies. We do not now allude to maladies caused by parasites, like the sickness of the vine, due to the oïdium Tuckeri, the sickness of the petals, caused by other small mushrooms, that of the rose-tree, the olive-tree, of corn, &c., produced by parasitical cryptogams, which fix themselves on the plant, and change the normal course of its life; we speak of morbid affections, properly so called. The pathological condition and its consequences exist in the plant as in the animal. Stoppage, or febrile and abnormal acceleration of the sap in the vegetable, answer to stagnation of the blood, or its acceleration during fever, in the animal; various excrescences of the bark, analogous to affections of the skin; the abortion of certain organs, and the capricious development of others; the secretion of pathological liquids which flow outside. This is a brief catalogue of the maladies to which trees, shrubs, and herbaceous vegetables are subject. A plant which passes too quickly and too often from intense cold to extreme heat, soon becomes ill, and necessarily perishes, like an animal exposed to those dangerous alterations. A shrub left in a current of cold air could no more live than an animal if kept in a similar place. In a word, the plant exhibits health or sickness, according to its conditions of existence. How can we admit that the being in which such changes take place, can be merely the passive subject of them, that it experiences neither pain nor pleasure in passing from health to sickness, or from sickness to health?
7. Sicknesses, or other causes, produce anomalies of form, or irregularities of structure in plants, as in animals. Just as in the animal kingdom monstrosities exist, there are monstrosities in the vegetable kingdom. The science which occupies itself with monstrosities in animals is called teratology. Geoffrey St. Hilaire has made some most interesting studies of the causes of the productions of monsters in the different classes of animals; but it has been perceived of late that an analogous science must be created, for the explanation of monstrosities proper to the vegetable kingdom, and Moquin Tandon has published a book upon vegetable teratology.
8. Old age and death are common to both plants and animals. Plants, after having survived the various maladies which threaten them, do not escape a slow old age, and death necessarily follows. With time, their vessels become hardened, their size becomes reduced, they can no longer give passage to the sap, or other liquids which ought to go through them. Liquids are not aspired with the same regularity, they no longer transude through the vegetable tissue with the same precision; they remain stagnant in the vessels, become corrupt there, and transfer their decomposition to the vessels which enclose them. Thenceforth the vital functions cease to be performed, and the plant dies. Things happen in a like manner among animals. The thickening of the vessels, the decrease of their power bring on the condition of old age, in which the functions are disturbed and slackened; then comes death, the inevitable end of all, in each kingdom of nature.
Thus, when we compare animals and plants, and especially when we consider the inferior beings in both kingdoms, it is impossible to establish a precise line of demarcation between them. The characteristics by which the old naturalists defined the distinction between plants and animals, are now acknowledged to be without meaning, and this distinction becomes more and more difficult in proportion as we make progress in our knowledge of these creatures. Voluntary motion was regarded as the principal distinctive characteristic between the two kingdoms of nature; but at the present day this characteristic can no longer be invoked. Elementary works on botany now tell us about the fly-catching plant, which catches the insect that crawls over its leaves, exactly as a spider catches flies, and about the oscillating plant, whose leaves are endowed by voluntary motion, more distinct than that belonging to many animals.