Page:History of botany (Sachs; Garnsey).djvu/204

 doubts respecting matters of detail. Hofmeister's researches in morphology and embryology ('Vergleichende Untersuchungen,' 1851) threw an entirely new light on the relations of affinity between the great groups in the vegetable kingdom, and were leading more and more to the view, that there must be some special peculiarity in the question of the constancy of organic forms. But the idea of evolution in the vegetable kingdom was brought more distinctly home to men's minds by palaeontological researches; Sternberg (1820-1838), Brongniart (1828-1837), Goeppert (1837-1845), and Corda (1845) made the flora of former ages the subject of careful study, and compared fossil plants with living allied forms. Unger especially, while advancing the knowledge of the structure of cells and of vegetable anatomy and physiology, and generally taking a prominent part in the development of the new botany, applied the results of its investigations to the examination of primeval vegetation, and showed the morphological and systematic relations between past and existing floras. After twenty years of preliminary study he declared distinctly in 1852, that the immutability of species is an illusion, that the new species which have made their appearance in geological periods are organically connected, the younger having arisen from the elder. It was shown in the former chapter, how about the same time the leading representative of idealistic views, Alexander Braun, was driven to the hypothesis, though in a more indefinite form, of an evolution of the vegetable kingdom: and in the year that Darwin's book on the origin of species appeared, Nägeli ('Beitrage,' ii. p. 34) wrote:—'External reasons, supplied by the comparison of the floras of successive geological periods, and internal reasons given in physiological and morphological laws of development and in the variability of the species, leave scarcely a doubt that species have proceeded one from another.'