164 



den change in character among the fungi. The evidence from Edgerton, 

 Shear and Wood, and Dastur, while not so complete, is strong collaterally. 

 It would seem from all this evidence that this phenomenon is common 

 and widely distributed among the fungi, though unquestionably it is more 

 common in some species and races than in others. 



TAXONOMY 



The classification of these Helminthosporium "forms," indeed of all 

 the fungi imperfecti, presents unusual difficulties. That they are only 

 "forms" of which we do not yet know the ' 'perfect" stage, is no more 

 relief from the necessity of classification than is incomplete knowledge 

 adequate reason for delay in attempts to classify other plants. In the 

 present instance some well-defined "species," in the old sense of the word, 

 stand out for example H. ravenelii while, on the other hand, several 

 of the strains of Helminthosporium in my collection differ in one or more 

 slight ways yet agree with each other closely in general type. For ex- 

 ample, my H. No. 1, H. No. 11 (isolated by Stakman from wheat in Min- 

 nesota), H. No. 13, isolated by Durrell in Iowa, H. No. 23, isolated by 

 Weniger in North Dakota, and an unnumbered one isolated by Hoffer 

 in Indiana, are all clearly the same general type of organism, and yet 

 they differ from each other in minor particulars. 



It is evident that we have in the genus Helminthosporium large 

 numbers of races that vary consistently and constantly, though but slightly, 

 from each other. These variations may be morphological in the usual 

 sense of the term, or as shown in cultures, or as demonstrated biomet- 

 rically. It is quite probable that here, too, there are, as elsewhere in the 

 fungi, differences in virulence, and therefore in biologic relationship, and 

 physiologically. Examples are numerous among the fungi where such 

 comparatively minor differences are regarded as of specific rank and the 

 new group is designated by a new binomial. There are also numerous 

 examples where such slightly variant types are regarded as varieties or 

 races 0f the species. These varieties or races have been variously desig- 

 nated as follows (or by the equivalents of these terms in other languages) : 



Physiological species (Hitchcock and Carleton 67) 



Species sorores (Schroeter 101) 



Biologische Spezies (Klebahn 73) 



Biologiske Arten (Rostrup 95) 



Schwester Arten (Schroeter) 



Biologische Rassen (Rostrup 95, 96) 



Specialisirte Formen (Eriksson) 



