154 Plant Genetics 



the most important material in plant genetics today it is 

 very desirable that the histology of the sac should be 

 investigated in detail. It will be realized that xenia 

 supplies a very convenient index for breeders. Corn 

 breeders especially must realize fully the fact of xenia, 

 and they are able to work more intelligently if they under- 

 stand the mechanism, since the principal work in corn 

 breeding has to do with the character of the endosperm. 



Having introduced the phenomenon of double fertili- 

 zation in connection with xenia, its use in explaining other 

 things than the mere fact of xenia may be considered. 

 It will be recalled that East (2) has done a large amount 

 of experimental work with sweet and starchy corn. 

 Careful examination enabled him to distinguish two 

 distinct races of starchy corn. Both races of course had 

 starchy grains, but the starch seemed to be laid down 

 in different ways in the two races. In one race the 

 starch occurred in a loose powdery or floury condition, 

 while in the other race it was compacted into a hard, 

 flinty, or so-called corneous condition. The two races, 

 therefore, may be spoken of as floury and corneous races 

 of starchy corn. 



East made various crosses between these two races 

 to discover the method of inheritance of the two endo- 

 sperm characters. Naturally such characters would 

 be expected to show xenia. In the following descrip- 

 tion, therefore, when the Fi generation is referred to, 

 both the hybrid embryo and the hybrid endosperm 

 surrounding it will be included. 



When East used the floury race as the pollen parent 

 and the corneous race as the ovule parent, the Fi genera- 

 tion was all corneous. When he made the reciprocal 



