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THE A M ERIC AN XA T URAL IS T [ Vol. LI 



tion of a difference in one pair of genetic factors. It may 

 be that awnlessness is a definite character which is a true 

 allelomorph of the fully-awned condition. Some might 

 prefer, however, to consider awnlessness simply as the 

 absence of awning. In that case we must assmne the 

 presence of an inhibitory factor to account for the partial 

 dominance of the awnless Sixty-Day over the weak-awned 

 Burt. The data at hand seem to point to the presence of 

 an inhibitor to awning in the variety Sixty-Day. A pre- 

 ponderance of awnless yellows in F2 and F3 suggests a 

 linkage of this inhibitory factor with the factor for yellow 

 color in the Sixty-Day. (See Table VII.) Such a finding 

 would be in agreement with the results of Nilsson-Ehle 

 (1914). A very definite linkage of the inhibitory factor 

 with the factor for yellow color has already been observed 

 in a cross between A. fatua and A. sativa var. Sixty-Day. 

 This will be brought out in a later publication. 



TABLE VII 



Certain other crosses with the Burt show that this 

 variety contains a factor for yellow which does not inhibit 

 awning. In the crosses Burt (red) X Swedish Select 

 (white), and Burt X Early Champion (white), the Fo con- 

 tained a certain number of yellow-seeded plants, which in 

 turn gave some yellows in Fo. All of these yellows were 

 fully awned. The existence of this yellow factor in the 

 variety Burt has complicated the study of the yellow of 

 the Sixty-Day in these crosses . The fact of the presence 

 of this yellow in the variety Burt should be kept in mind 

 when Table VII is examined. 



It will be seen in Table VII, that the red grains are 

 nearly as numerous in the 100 per cent, class as in the 



3 The classes are as follows: -0, 1-10, 11-20, . . . ., 91-99, -100. 



