THE SPECIES CONCEPT FROM THE POINT OF VIEW 
OF A PLANT PATHOLOGIST 1 
E. C. Stakman 
To the plant pathologist the problem of the species concept is not 
only of academic interest but also of intense practical importance. While 
pathologists as well as other botanists love to seek truth for truth’s sake, 
most of them are under obligation to seek the truth for the good it may do 
in the complex process of preventing the world from starving. The delimi¬ 
tation of species is prerequisite to the experimentation and research of the 
pathologist. It is essential that the specific purity both of the host plant 
and of the pathogene be known. If these fundamental facts are not assured, 
the pathologist is likely to find not truth but error; or, at best, the truth 
is in danger of being badly garbled. The accurate description of species, 
then, is of primary importance, but it is not an end in itself, but only the 
means to an end. However, being the means to an end, the accurate 
description of pathogenic fungi is of greater practical importance to pathol¬ 
ogists than to any other class of botanists. 
It is to be hoped that there will be no unduly severe criticism on account 
of what may seem to some an ultra-utilitarian viewpoint. The fact is 
that the pathologist must learn the effect of pathogenes on the host plant. 
In order to do this, he first must know thoroughly both the pathogene and 
the host plant. He must depend, therefore, on systematic mycology and 
other systematic botany for the tools of his trade. If the tools be unsuitable 
for his work, either he must improve them or he must make his own. There¬ 
fore it is pertinent to inquire what quality of tools have been furnished 
him in the past. 
To the taxonomist of higher plants, and particularly to the geneticist, 
the pathologist is indebted for the proper attitude toward the host plants 
which he uses. The geneticists have given us the pure-line conception for 
higher plants. Pathologists now are avoiding many serious mistakes by 
taking the simple but fundamental precaution of using pure-line host 
material. For example, wheat generally has been considered to be close- 
pollinated. But Hayes has shown that natural crossing may occur in the 
field. Supposing, then, experiments are made on the biologic specialization 
of pathogenic fungi attacking varieties of wheat; what reliance can be 
placed upon the results when bulk material of wheat seed is used? Some 
of the plants very likely will be heterozygous for resistance. This may 
1 Read in the symposium on “The Utility of the Species Concept,” at the joint meeting 
of Section G of the American Association for the Advancement of Science, the American 
Phytopathological Society, and the Botanical Society of America, at Toronto, December 
28, 1921. 
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