142 



Plant Genetics 



with those of the earlier generations. Also he has 

 discovered two new pure races of beans which give 

 similar results. It remains to be seen whether this 

 explanation will fit other cases of semi-sterility. 



This theory of semi-sterility of course may have 

 some value in throwing light upon the problem of com- 

 plete self-sterility. It seems to be of greater theoretical 



interest, however, in 

 being the first attempt 

 to include inheritance in 

 gametophytes in an ex- 

 planation of Mendelian 

 results. BELLING him- 

 self does not stress this 

 gametophyte relation- 

 ship ; in fact, he does not 

 use the word " gameto- 

 phyte"; and yet it is 

 probably this gameto- 

 phyte relationship that 



FIG. 33. Diagram showing how 

 the F 2 would be produced according 

 to BELLING'S idea of semi-sterility. 



represents the most 

 significant feature of his 



work and will prove to be the most suggestive feature 

 in future investigations. 



Attractive as this explanation may be, we must 

 realize, however, that as yet it merely explains semi- 

 sterility and does not clear up the fundamental com- 

 plexity of the more general topic of self-sterility, that is, 

 why pollen fails on "own" stigmas and functions on 

 foreign stigmas. 



Very recently an explanation of the more general 

 problem of self-sterility has been proposed by EAST 



