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 of 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—?5, 96) 
Specialisirte Formen (Eriksson) 
