858. Systematic botany relates to the arrangement of plants into groups and families, according to their characters, for the purpose of facilitating the study of their names, affinities, habits, history, properties and uses.
859. In this department, the principles of Structural and Physiological Botany are applied and brought into practical use in the discrimination of the different groups, and the limitation of their characters. Besides the immediate uses of Systematic Botany in the determination of species and kinds, as above stated, it accomplishes
860. Another purpose of still higher import. It aids us in studying plants as related to each other, and constituting one great and glorious system. It shows us the Almighty Creator at once employed in the minutest details and upon the boundless whole, equally attentive to the perfection of the individual in itself, and to the completeness of the grand system, of which it forms a necessary part.
861. The subject of great extent. The study of classification introduces the botanist into an extensive field of inquiry. The subjects of his research meet him at every step. They clothe the hill and plain, the mountain and valley. They spring up in the hedges and by the way side. They border the streams and lakes and sprinkle over their surfaces; they stand assembled in vast forests, and cover with verdure even the depths of the ocean. Now, with each individual of this vast kingdom the botanist proposes to acquaint himself, so that he shall be able readily to recognize its name, and all that is either instructive, interesting, or useful concerning it, whenever and wherever it is presented to his view.
862. The wrong way to study. Now it is obvious that if the student should attempt the accomplishment of this labor by studying each and every individual plant in detail, whether with or without the aid of books, the longest life would scarcely suffice him for making a good beginning. But such an attempt would be as unnecessary as fruitless. The Author of Nature has grouped these myriads of individuals into
863. Species (§ 76). When He called plants into existence, in their specific forms, He endowed each with the power of perpetuating its own kind and no other, so that they have descended to us distinguished by the same characters and properties as at the beginning. When, therefore, the student has formed acquaintance with any individual plant, he is also acquainted with all other individuals belonging to the same species.
864 For example: a single plant of white clover is a true representative of all the millions of its kind that grow on our hills and in our meadows; and a single description of the white pine will answer in all essential points for every individual tree of that noble species, in all lands where it is found.
865. Genera. Although the species are separated from each other by clear and definite distinctions, still they are found to exhibit also constant affinities, whereby they stand associated into larger groups called genera (§ 80). A genus, therefore, is an assemblage of related species, having more marked affinities with each other in general structure and appearance than they have with other species.
8GG. For example: the white clover and the red (Trifolium repens and T. pra-tense) are universally recognized as different species, but of the same genus; and a single generic description of one plant of the genus Trifolium will convey intelligence to a certain extent concerning every other plant belonging to its 150 species.
867. Thus are the individual plants of the globe grouped by descent and resemblance, and comprehended under species; and the species associated into higher groups called genera. "An individual," says Prof. Forbes, "is a positive reality; a species is a relative reality; a genus is an idea - but an idea impressed on nature, and not arbitrarily dependent on man's conceptions. An individual is one: a species consists of many resulting from one; a genus consists of more or fewer of these manies resulting from one linked together, not by a relationship of descent, but by an affinity dependent on a Divine idea."
868. Orders. But natural affinities do not end here. The genera are yet too numerous for the ready and systematic study of the naturalist. He, therefore, would generalize still further, and reduce the genera to still fewer and broader groups. On comparing the genera with each other, he finds that they also possess in common certain important characters which are of a more general nature than those which distinguish them from each other. By these general characters the genera are associated into orders.
869. For example: comparing such genera as the mustard, radish, cabbage, cress, wall-flower, etc., it is seen that, while they differ sufficiently in their generic characters, yet they all have certain marked resemblances, in their didynamous stamens, siliquous fruit, whereby they are obviously associated into the same order - the Cruciferae. So, also, the pines, the spruces, the cedars, the larches, and the cypress, while as genera they are obviously distinct, yet all bear cones of some form, with naked seeds; hence they are naturally grouped into one Order - the Coniferae.
870. Classes. In like manner the Orders, by characteristics of resemblance still more general, are associated into a few groups, each of great extent, called Classes whether natural or artificial
871. Intermediate groups, formed on the same principles, are recognized as Subgenera, Suborders or Tribes, and Subclasses or Cohorts, which will be further noticed and described in another place.
872. Methods OF classification. Two independent and widely different methods of classifying the genera have been generally approved, the Artificial System of Linnaeus, and the Natural System of Jussieu. The former is founded solely on characters relating to the organs of fructification, leaving all other natural affinities out of view. The latter, on the contrary, takes for its basis all those natural affinities and resemblances of plants whereby Nature herself has distinguished them into groups and families.