the Cryptogams, then questions arose on which the dogmatic philosophy had not essayed its ancient strength; the facts and the questions were new and untouched, and presented themselves to unprejudiced observation in a purer form than those, which during the first three centuries had been so mixed up with the old philosophy and with the principles of scholasticism. Von Mohl, who only occasionally occupied himself with morphological subjects, was a firm adherent of the inductive method, and was bent on the establishment of individual facts rather than of general principles; but the founders also of the new morphology, Schleiden and Nägeli, started from philosophical points of view, which, different as they were in the two men, had yet two things in common, a demand for severely inductive investigation as the foundation of all science, and the rejection of all teleological modes of explaining phenomena, in which latter point their opposition to the idealistic nature-philosophy school was most distinctly manifested. They had indeed one very important point of contact with this school, the belief in the constancy of organic forms: but this belief, not being connected with the Platonic doctrine of ideas, was with them only a recognition of every-day observations, and was therefore of less fundamental importance, being felt merely as an inconvenient element in the science. Treating the question in this way, and influenced by the results of the new researches, they either inclined to entertain the idea of descent before the appearance of Darwin’s great work, or gave a ready assent to the principle of the new doctrine, though they expressed some 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