156 Plant Genetics 



The conclusion is therefore that this is not a true case 

 of maternal inheritance. East offers a very reasonable 

 explanation of these results, based upon double fertiliza- 

 tion plus the cumulative factor idea. These characters 

 appear superficially to be maternal for the following 

 reasons. The endosperm nuclei are ^x, 2X from the 

 female and ix from the male. In the characters under 

 discussion the presence of two factors always dominates 

 the presence of one factor; thus corneous female crossed 

 with floury male produces progeny which are all pheno- 

 typically (in appearance) corneous, while floury female 

 crossed with corneous male for the same reason produces 

 progeny which are all phenotypically floury. The 

 cumulative factor idea will be recognized. The mother 

 always determines the character of the hybrid endo- 

 sperm because there are always two female nuclei to 

 predominate over the single male nucleus. In the 

 embryo, however, this predominance does not occur, 

 for there only a single female nucleus has fused with 

 a single male nucleus. When this hybrid embryo 

 matures, therefore, it is evident that it will produce 

 gametes of two sorts, 50 per cent corneous and 50 per 

 cent floury. It is evident that the female is really the 

 only decisive factor, so far as the appearance of endo- 

 sperm is concerned, so that the ratios appearing among 

 the female gametes in the Fx generation will be the 

 ratios that will appear also in the F2 endosperms. In 

 other words, 50 per cent of the Fj endosperms will be 

 corneous and 50 per cent floury, no matter what may 

 be the source of the pollen. It is obvious that the 

 explanation of this peculiar form of apparently maternal 

 inheritance depends entirely upon a clear conception of 



