276 



Shull. 



must have been some fundamentally important genotypic feature of the 

 narrow-leafed males used in these crosses is obvious from several con- 

 siderations. The consistency of the results in every mating, regardless 

 of the fact that four different males were used, shows that this absence 

 of females must be due to something more fundamental than a mere 

 individual idiosyncracy, and the same conclusion is further impressed 

 by the results of crosses between these same narrow-leafed males and 

 homozygous broad-leafed females, as given in Table II. 



(b) Crosses between homozygous broad-leafed females and the F 2 

 narrow-leafed males. 



As the homozygous broad-leafed female is here assumed to have 

 the formula XBF.XBF and the homozygous angustifolia-malQ XbF.Xbf 

 there are only two classes of offspring expected; namely, 



XBF.XbF = heterozygous broad-leafed females, 

 XBF.Xbf heterozygous broad-leafed males. 



The results are given below in Table II. This table is divided into 

 two sections; the first section contains 17 sib-crosses and the second 

 presents the results of five " out-crosses" in which the same narrow- 

 leafed males were used. 



Table II. 



Formula: XBF.XBF X XbF.Xbf. 



