PLANT, a living organic being, destitute of any indication of mind or feeling, and sometimes defined as essentially differing from an animal in the want of voluntary motion. Plants are the organisms which form the vegetable kingdom; the science which treats of them is botany (q.v.). Plants of higher organization can never be mistaken for animals, nor animals of higher organization for plants. But there is no regular ascend ing and descending scale of organisms, from the highest animal to the lowest plant; instead we find a widely extended base from which the ascent seems to begin at once in both the organic kingdoms, with many ramificetions in each; and in the case of the low est groups of either kingdom, it is sometimes dillicult to disCern the difference between plants and animals. The difficulty may be owing to our ignorance and incapacity of proper observation.
Something which resembleS the voluntary motion of animals is to be seen in some plants, in various phenomena of irritability (q.v.); and there is even locomotion in the vegetable kingdom wonderfully simulating voluntary locomotion, a provision of nature for the diffusion of some of the lower vegetable organisms; the gonidia (q.v.) of algae and the spermatozoidia (q.v.) of some other cryptogainons orders moving in a surrounding fluid by means of cilia, so that they have often been mistaken for animalcules. lint no motion which can really be deemed voluntary takes place in the vegetable kingdom; and no animal, certainly to be pronounced such. fails to exhibit it—even when there is no power whatever of locomotion—in the prehension of food, or for some of the purposes of life.
The general laws which govern life prevail in plants as in animals. There are organs of nutrition and organs of reproduction; the whole being made up of organs, and every organ destined to maintain the existence either of the individual or of the race. But them is nothing in plants corresponding to the mouth, stomach, and alimentary canal of animals. Nutrition takes place in a different manner; assimilation being effected by a process very unlike that of digestion in animals. There are, however. animals destitute
of a mouth, stomach, and alimentary canal; so that the distinction between plants and animals cannot be stated so absolutely in this respect as in respect to voluntary motion; and as there are many plants which have no roots, nutrition by, means of roots, although peculiar to the vegetable kingdom, is not its distinguishing characteristic. The nutri ment of plants is derived either by their roots from the soil (see How), or through the integuments of their other parts from the air or water in which they live; and all their nutriment is either liquid or gaseous, being taken up in the former case by enilosmose (q.v.), and in the latter case through stomata (q.v.). Many plants, and among them the greater number of phanerog,amons plants, owe their nourishment both to the soil and to the atmosphere, their roots deriving it from the former, and the leaves (q.v.) of plants that have leaves being the principal organs by which they derive it from the latter. When leaves are wanting, the integument of the parts exposed to the air the functions ordinarily assigned to them. Solid matter cannot be appropriated by plants until it has been dissolved in water, or decomposed. See MANURE and Som.—The nutri ment appropriated by the plant is not assimilated until it has undergone chemical changes, which sometimes take place entirely within the very cell through the integu ment of which it has entered, sonic of the lowest kinds of plants consisting altogether only of a single cell, but which, in other plants of higher and more complex organization, depend upon a circulation of the sap (q.v.), and a very various action of many different organs, each formed of a multitude of cells. These processes are still very imperfectly understood. By them, not only is the plant nourished, but vegetable products of every kind are elaborated, in which, throughout the wide domains Of the vegetable kingdom, there is such wonderful variety, and often great diversity in different parts of the same plant.