the species, be assumed as equally or even more operative through long anterior periods, this would account for the diversification of an original species of a genus into several or many forms as different as those we recognize as species. But this would not account for the limitation of species, which is the usual characteristic, and is an essential part of the idea of species. Just this is accounted for by natural selection. This now familiar term, proposed by Darwin, was suggested by the operations of breeders in the development and fixation of races for man's use or fancy—breeding in each generation those individuals only in which the desired points are apparent and predominant: in the seed-bed, by rigidly destroying all plants which do not show some desirable variation, breeding in and in from these with strict selection of the most variant form in the particular line or lines, until it becomes fixed by heredity, and as different from the primal stock as the conditions of the case allow. In nature, the analogous selection, through innumerable generations of the exceedingly small percentage of individuals (as ova or seeds) which ordinarily are to survive and propagate, is made by competition for food or room, the attacks of animals, the vicissitudes of climates, and, in fine, by all the manifold conditions to which they are exposed. In the struggle for life to which they are thus inevitably exposed, only the individuals best adapted to the circumstances can survive to maturity and propagate their like. This survival of the fittest, metaphorically expressed by the phrase natural selection, is, in fact, the destruction of all weaker competitors, or of all which, however they might be favored by other conditions, are not the most favored under the actual circumstances. But seedlings, varying, some in one direction and some in another, are thereby adapted to different conditions, some to one kind of soil and exposure, some to another, thus lessening the competition between the two most divergent forms, and favoring their preservation and further separation, while the intermediate forms perish. Thus an ancestral type would become diversified into races and species. Earlier variation, under terrestrial changes and vicissitudes, prolonged and various in geological times since the appearance of the main types of vegetation, and the attendant extinctions, are held to account for genera, tribes, orders, etc., and to explain their actual affinities. Affinity under this view is consanguinity; and classification, so far as it is natural, expresses real relationship. Classes, orders, tribes, etc., are the earlier or main and successful branches of the genealogical tree, genera are later branches, species the latest definitely developed ramifications, varieties the developing buds. Briefly: Taken as a working hypothesis, the doctrine of the derivation of species serves well for the coordination of all the facts in botany, and affords a probable and reasonable answer to a long series of questions which, without it, are totally unanswerable. It is supported by vegetable paleontology, which assures us that the plants of the later geological periods are the ancestors of the actual flora of the world. In accordance with it we may explain in a good degree the present distribution of species and other groups over the world. It explains, by inheritance, the existence of functionless parts, throws light upon the anomalies of parasitic plants, and, indeed, illuminates the whole field of morphology with which this volume has been occupied.