SPECIES HYBRIDIZATION 



237 



ticularly striking. Those F i hybrids are completely sterile with their own 

 pollen. However, it was possible by pollinating the hybrids either with 

 pollen from wheat or rye to obtain a few viable seeds. For wheat pollina- 

 tion the ratio of success was about 3 in one thousand; for rye only one 

 plant was secured from nearly five thousand trials. The pollen grains of 

 the hybrids were apparently completely non-functional, and cytological 

 examination indicated prevailingly irregular divisions and behavior in 

 their production. 



The product of back-crossing the F\ hybrids to wheat gave plants 



B 



U: 







B 



FIG. 100. Sterile hybrids be- 

 tween wheat and rye, A, the wheat 

 parent; C, the rye parent, and B, 

 the Fi hybrid between them. 



(After Jesenko.) 



Fia. 101. Sesqui-hybrids from the Fi wheat X 

 rye crossed back to wheat. (After Jesenko.) 



very similar to wheat. This is illustrated in Fig. 101. Although all 

 these plants resembled wheat in their general characters, they neverthe- 

 less showed wide differences from one another, not only in morphological 

 characters but in physiological ones such as fertility as well. A few of 

 the plants were totally sterile, but some of them were more or less fertile 

 and in general those were most fertile which most closely resembled the 

 wheat parent. In the next following generation, the progeny of those 

 plants which were most fertile consisted of plants which were apparently 

 pure wheat and completely fertile and plants which were less like wheat 

 and- showed lessened fertility as the resemblance to wheat decreased. 



