150 Outline of Genetics 



The conclusion is that this is not a true case of mater- 

 nal inheritance. East offers a very reasonable explana- 

 tion of these results, based upon the peculiarities of 

 double fertilization. These characters appear super- 

 ficially to be maternal for the following reasons. 

 The endosperm nuclei are 30:, 2x from the female and x 

 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 that are all phenotypically corne- 

 ous, while floury female crossed with corneous male for 

 the same reason produces progeny which are all pheno- 

 typically floury. The mother always determines the 

 character of the hybrid endosperm because there are 

 always two female nuclei to predominate over the single 

 male nucleus. In the embryo, however, this predomi- 

 nance does not occur, for there only a single female 

 nucleus has fused with the 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. Since the female is really the 

 only decisive factor, so far as endosperm is concerned, the 

 ratios appearing among the female gametes in the Fj 

 generation will be the ratios that will appear also in the 

 F2 endosperms. In other words, 50 per cent of the F, 

 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 the phenomenon of triple fusion. 

 Conversely, this type of inheritance indicates that the 

 triple fusion, instead of being merely a meaningless 



