Reed: The mildews of the cereals 387 



is susceptible, nor do we know to what extent immunity or sus- 

 ceptibility to a given disease can be transmitted from parent to 

 offspring. The influence of external conditions, the factors of a 

 plant's environment, is yet to be worked out. Further investiga- 

 tions with these resistant varieties and their hybrids should throw 

 considerable light on this question. 



I desire to express my appreciation of Professor R. A. Harper's 

 and also Professor C. Stuart Gager's kindness in reading the manu- 

 script of this paper and for many valuable suggestions. 



University of Missouri, 



Columbia, Mo. 



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