380 KARL WILHELM VON NAEGELI. 



Although interesting and suggestive, they hardly possess the same 

 weight as his other writings. He differs with many recent writers 

 in believing that, among forms like bacteria, it is dovibtful whether 

 definite species exist, morphologically speaking, as in higher plants. 

 It is still too soon to say whether his view on this point is correct 

 or not; for, although most bacteriologists do not now agree with 

 Naegeli, it must be admitted that the question is still an open one, 

 and it Avould be rash to predict what would be the general verdict 

 on this point a decade hence. 



Up to this point we have spoken only of the special work which 

 entitles Naegeli to be regarded as one of the foremost botanists of 

 his time, unsurpassed and jDerhaps unequalled in his own special 

 field. But his influence was felt beyond purely botanical circles, 

 and he acquired by his writings on evolution a wide-spread repu- 

 tation among all scientific men. In his doctor's thesis (1840) on 

 the Swiss species of Cirsium, Naegeli foreshadowed a line of study 

 which he afterwards worked out more elaborately in his later work 

 on Hieracium, in which he made a minute and critical study of the 

 variable species of a large genus serve as a groundwork for a con- 

 sideration of the theory of descent. Early in life he believed in 

 the absolute difference of species, although he urged the necessity 

 of the study of development as that which gives real value to the 

 knowledge of mature forms. In a later work, however, he stated 

 that this early belief in the absolute difference of species 'Mid 

 not prevent his believing even then in the origin of species by 

 descent." In his important paper, '*Die Entstehung und Begriff 

 der naturhistorischen Art " (1865), he discussed the Darwinian view 

 of the origin of species, and stated that his own belief in the origin 

 of species by descent had been definitely expressed in a paper pub- 

 lished in 1856. He differed with Darwin in believing that varia- 

 tion occurred in a definite direction, — a view similar to that held 

 by Gray, — and he was unable to accept natural selection as a 

 sufiicient explantion of evolution. His views were peculiar in 

 that he believed that the different groups of plants originated inde- 

 pendently from what he called " Urzellen," and, taking the differ- 

 ent groups as they now exist, he failed to recognize a gradual 

 development of the higher forms from the lower. Without stop- 

 ping to consider his papers on the influence of external conditions 

 in the formation of varieties and the theory of hybrid formation, we 

 need here only refer to ''Die mechanisch-physiologische Theorie 

 der Abstammungslehre " (1884), a work in which he states the 



