SPECIES HYBRIDIZATION 237 
ticularly striking. These F’; 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 
Fig. 101.—Sesqui-hybrids from the F; wheat 
Fie. 100.—Sterile hybrids be- 
rye crossed back to wheat. (A/fler Jesenko.) 
tween wheat and rye, A, the wheat 
parent; C, the rye parent, and B, 
the F: hybrid between them. 
(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. 
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