The necessity of classification and systematic arrangement in B. will be very obvious, if the multitude of different kinds of plants is considered, fully 120,000 species being already known and described, 'Whilst great regions of the earth are still unexplored. The systematic arrangement of plants is sometimes called systematic B., sometimes taxologieal B. (Gr. taxis, ta der, and logos, a discourse), sometimes, less properly, taxology or taxonomy. The history and progress of the science have been marked by the different s2.stems which have been proposed, and have prevailed at different times. These have, however, been of two very distinct kinds, founded upon very different principles, and particularly adapted to very different objects, and are respectively designated artificial and natural or physiological systems. Artificial systems are based upon some single class of charac ters, in the external parts of plants, without reference to the importance of these characters in what concerns the life of a plant, or the purpose for which it exists, and are chiefly adapted to the convenience of the student desirous of readily distinguishing species among the multitudes with which he has to deal. A work of descriptive B., arranged according to an artificial system, has been aptly likened to a dictionary in which the words are alphabetically arranged.
An artificial system cannot, however, serve the highest purposes of the science. But in framing a natural system, great difficulties are to be encountered, and imperfection of the system is necessarily to a certain extent involved in imperfection of the science. Based not upon one mere set of characters arbitrarily selected, but upon a'consideration as far as possible of all characters which plants present. and not merely upon external forms viewed in themselves. hut upon these and internal organization considered in their physiological relations. a natural system aims at exhibiting the real affinities which subsist in the vegetable kingdom; and evidently must be at all times liable to modifica tion, and capable.orimprovement, botanical science advandeS, either through the (Es cowry of new plantsor through phytotomieal and physiological research: it also evidently requires the greatest selentitic attainments and the highest powers of a philosophic mind. i Nor s it one of the least of the practical difficulties, that the affinities of plants are not such as to constitute a simple lineal series, but that they may be viewed as a multitude of groups arranged around centers, and connected with each other upon different sides and lie a great variety of ties.
Yet the of a natural system have always been sought after, and in some measure attained, when B. has been studied as a science—whenever it has become any thiug more than a mere acquaintance with a few plants and their names. The golera into which species are grouped by all botanists are natural. and are the basis upon which
all classification proceeds in its further generalizations. So sensible. was Linnseus of the importance of maintaining this character of the genera, that when a rigid adherence to his artificial system would have caused the division of a genus into parts, and the conse quent separation of species very nearly allied, he kept the genus unbroken, and main tained the usefulness of his artificial system, to the student desirous of finding the names of plants, by referring from one of its classes or orders to another for speciesexceptioual among; those of their genus as to the number of their stamens or pistils, or their dim rionot, moweients, or hermaphrodite flowers.—The classification of species, however, in genera and larger natural groups, being a subject as much connected with other branches of natural history as with B., \VW more properly be treated in the article NaTunAL IfISTORY; and to that article also, and to the article SPECIES, we refer for all that our limits allow concerning some of the most interesting and difficult questions of science. the limits of species, the distribution of species, etc.
An important branch of botanical science is that which is called geographical P., or the geography of plank,, and sometimes phytogeography. It must be regarded as yet in its infancy, although a multitude of observations have been recorded in works of descriptive B, and by botanical travelers. It is the object of geographical B. to connect with the occurrence or prevalence of plants in particular countries a great variety of facts as to climate, altitude, geology, etc., and even facts of history. It aims at the establishment of great general laws, which, however, it has not yet been able to establish. Some account of the progress which has been made in this branch of B.. and of the imperfect generalizations which have been reached, will be found in the article Op PL;NTs.
Another branch of botanical science which has recently sprung up, and has acquired great magnitude and importance, is FALiEONTOLDGICAL B., or FOSSIL BOTANY. Tltc petrified fruits and wood, the beautiful impressions of ferns and palms, and other traces and remains of former vegetation, which appear in vast numbers and great variety in different strata of the earth's crust, present a most interesting field of scientific research. The study of the different kinds of fossil plants, mid the comparison of them with exist ing species, belong strictly to the science of B.: the study of their relations to particular strata or formations, and so to particular periods in the physical history of the globe, belongs to geology. The study of fossil plants has proved exceedingly useful in guid ing to just and philosophic views of the mutual relations even of species and groups still existing. See PALALoyroLoov.