1915] 



APPEL — PHYTOPATHOLOGY AND SCIENTIFIC BOTANY 279 



Much more difficult are the systematic relations of the 

 fungi. Many experiments and publications are valueless 

 because the identity of the fungus was not made sure of in 

 every single case. These difficulties are greater in case the 

 fungi in question belong to the Fungi Imperfecti, where very 

 often only the name of the genus has been determined, while 

 the species name was simply made from the name of the host. 

 Moreover, the descriptions of these imperfect fungi are often 

 so insufficient that it is impossible to identify the fungi after- 

 wards, especially when they occur on other plants or on a 

 different or unrecognizable substratum. Within a genus that 

 is rich in species there have sometimes been erected so many 

 species that there is no possibility of identification. We find 

 an instance of this in the genus Fusarium. Several hundreds 

 of species have been described; which of these are identical 

 has not yet been made clear, and in many cases this may never 

 be possible. We cannot always solve the problem by making 

 use of the exsiccata of the author of the species. Moreover, 

 on one species of host several species of Fusarium may be 

 harbored, and the author has often considered them identical. 

 It is further often impossible to find what fungus was the 

 type of the author's description. In such a case the only 

 alternative is a thorough reworking of the taxonomy. How 

 extensive a work this may often involve is instanced by the 



genus Fusarium. To establish the fundamental facts regard- 

 ing the taxonomy within this genus required four years of 



work on my part as well as on the part of my assistant, Dr. 

 Wollenweber, who devoted all of his time to the subject. 



Even after the establishment of these fundamental facts, 

 only a very small part of the species had been determined, and 

 for another two years Wollenweber has been working up the 

 remaining species. I wish only to point out in addition that 

 there exist more genera of this type : Botrytis, Gloeosporium, 

 and Alternaria and its relatives. 



Modern taxonomy of fungi cannot limit itself to the 

 morphology of the species casually collected. It must have 

 the help of pure cultures on various media, for in artificial 

 culture additional differences show themselves. These differ- 



