44 



of plant forms. Linnaeus, however, was wise enough to recog- 

 nize its artificiality. 



From Linnaeus the advance was more rapid, and, while most 

 of the study in plants centered on the work of classification, 

 there were unmistakable signs of other interests. The ideas of 

 ^he classifier were still hampered by the dogma of the constancy 

 of species, which continually clashed with the insistent and un- 

 deniable evidences of the genetic relationships of organic forms. 

 Despite the movement in favor of the idea of the development of 

 species from previously existing forms, despite the views advanced 

 by Lamarck and others at about that time, despite, indeed, the 

 more strictly botanical investigations in the morphological field 

 which were brought forward during the first half of the nine^ 

 teenth century : despite all these things, the botanist was unable 

 to break away from the concept of groups of plants as abstract 

 ideas. It was not until 1859 that the publication of Darwin's 

 " Origin of Species " drove biologists to a different point of view. 

 Then the rational idea of the evolution of organic forms explained 

 in a similar rational fashion the observed genetic relationships of 

 groups of plants. No longer did the classifier hesitatingly 

 admit the possibility of the evolution of species and deny that of 

 genera and higher groups, no longer did he maintain his artificial 

 groups, which had no more relation to each other than successive 

 throws of dice, but he admitted the whole great scheme implied 

 by the evolution of organic forms from preexisting types. 



Naturally, it is difficult to point out at just what time the 

 modern trend of botanical work found its origin, but one can 

 say, in a general way, that it was about the middle of the nine- 

 teenth century, although of the two criteria of progress to which 

 I shall refer, one dates about a decade before, the other about a 

 decade- after that time. The establishment by the botanist Schlei- 

 den in 1838, and by the zoologist Schwann in 1839, of the real 

 nature of the cell, and the acceptance of what may be termed the 

 cell doctrine, at once made possible the development of the study 

 of form and structure, both as to adult and as to embryonic 

 organs. With improved optical apparatus and with improved 

 teclinical methods, many able students added a vast number of 



