138 Plant Genetics 



by subsequent breeding work. Furthermore, it is the 

 first true Mendelian explanation that has been based 

 on the germinal constitution in the gametophyte as a 

 deciding factor. 



In 1914 Belling (i) published a paper entitled "A 

 study of semi-sterility." Apparently this is not true 

 self-sterility, but it is a closely related phenomenon and 

 may be considered in this connection. Belling was 

 conducting breeding experiments with two races of 

 beans, both of which were completely fertile. When 

 he crossed them, however, the resulting hybrids were 

 semi-sterile. Uniformly just one-half of the pollen 

 grains appeared empty and collapsed, while one-half 

 of the ovules had no embryo sacs. The sterile pollen 

 and ovules appeared in random distribution with the 

 fertile. 



Inbreeding the semi-sterile hybrids. Belling ob- 

 tained an F2 generation which showed the following 

 features: one-half the plants had perfect pollen, the 

 other one-half had a mixture of equal numbers of good 

 and bad pollen grains in all their flowers. The plants 

 which had perfect pollen also had perfect ovules, while 

 the plants with 50 per cent sterile pollen also had 50 

 per cent sterile ovules. In the F3 generation all the 

 descendants from the fertile plants had perfectly good 

 pollen and ovules; but the progeny of the semi-sterile 

 plants again split up into two classes (fertile and semi- 

 sterile) as before. 



Belling states his general conclusion as follows: 

 "The explanation of the random abortion of one-half 

 of the pollen and one-half of the embryo sacs must 

 apparently be by the segregation of Mendelian factors 



