MODERNBIOLOGY 43 5 



explain actual phenomena. That its theoretical possibility nevertheless still 

 continues to be keenly discussed is due to modern natural-philosophical 

 speculation — a subject that will be dealt with in a later chapter. 



4. Botany 



Plant classification after Linnaus 

 A SURVEY of the most important data in the history of botany, particularly 

 of plant classification, up to the period covered by our chapter heading, is 

 necessary if we are to obtain a universal view of the development of biology 

 during the period now being described. In order to obtain this view we must 

 first of all return to the days of Linnasus. It will be remembered that Linnaeus 

 set up, in the first place, an artificial system based exclusively on the structure 

 of the various parts of flowers and especially intended to be used for practical 

 examination purposes, and, in the second place, a natural system, based on 

 the common forms of plants — a system which he worked at throughout 

 his life, without, however, being able to find a satisfactory conclusion to it. 

 His immediate successors paid but little attention to this latter legacy from 

 him, although it really offers immense possibilities for development; they 

 contented themselves rather with examining as many new plants as possible 

 according to the sexual system. During this time, however, there were 

 published a considerable Tiumber of sound systematic works; the study of 

 cryptogams in particular made rapid progress, but nothing was contributed 

 to the development of the system itself until twenty years after Linnaus 's 

 days, when Jussieu's systematic work. Genera -plantarmn, was published. 



Antoine Laurent de Jussieu came of a family that had already given 

 France two eminent botanists, principally in the spirit of Tournefort; es- 

 pecially Bernard de Jussieu, uncle of the above-named, who had made con- 

 siderable additions to a natural system, without, however, succeeding in 

 completing it. A. de Jussieu was born at Lyons in 1748, studied medicine in 

 Paris, and became professor at the Jardin des Plantes, after which he held 

 some other botanical and medical posts and finally became professor of phar- 

 macy in the faculty of medicine. He was active for many years and attained a 

 great age; he died in 1836. In his principal work, mentioned above, Jussieu 

 has set up a complete natural vegetable system, the first of its kind. Like Ray, 

 he makes the cotyledons the chief basis of classification for the vegetable king- 

 dom; in his view this is justified, because the plant arises out of the seed, and 

 the latter's most vital part is the cotyledon — it is compared with the heart 

 of animals. Consequently plants are divided into: acotyledons, monocoty- 

 ledons, and dicotyledons, a system of classification that, thanks to him, has 

 become permanent. These three main divisions are then divided into orders. 



