WICnUEA ON HYBKIDS. G7 



tera, and Geum, there was a perpetual decrease of fertility and a 

 general decrepitude, though he does expressly state that this de- 

 pended on imperfection in the pollen. 



2. Different individuals of the same hybrid generation nearly 

 resemble each other in the degree of imperfection in the pollen. 

 This was found to be the case in all experiments with artificial 

 hybrids which for the most part yield a large number of male 

 plants. In wild hybrids, especially of the formula 



$ ( $ (« + &) + 6 (a + b) + 6 (a + b), &o, 

 it is very probable that individuals may be found in which the 

 different degrees of imperfection of pollen may be found in one 

 and the same hybrid. It is possible also that different individuals 

 of the same two species, when hybridizing, may yield different kinds 

 of irregular pollen. 



3. Distantly related species of willow, when combined in hybri- 

 dization, give a more irregular pollen than nearly allied species. 



4. The anomaly of pollen increases with the number of inter- 

 mingled species. 



S S. ( $ (Lapponum + silesiaca) spont. + S (purpurea +viminalis) 

 spont.) has far more sterile grains than S. (purpurea + viminalis) 

 and S. (Lapp onum + silesiaca) spont., which has proportionally 

 regular pollen, while even some ternary hybrids are quite sterile 

 though the parents are fertile. Again, the quinary $ S. ( $ (pur- 

 purea + rep ens) + S aurita) art. + (caprea -+viminalis) art.) has by 

 far a greater number of sterile pollen-grains than all the binary 

 hybrids which are known of its five parents. 



"We now arrive at the female flowers of the hybrids ; but unfor- 

 tunately this part of the subject has engaged Wichura's attention 

 much less than the former. It is indeed overwhelmed with diffi- 

 culties, and would require immense patience to follow it out pro- 

 perly ; for the contents of the embryo-sac could not be observed 

 so easily as those of the anthers. Professor Henslow went as far 

 as could be expected in this direction when he wrote his model 

 treatise on a hybrid Digitalis ; but more is required to satisfy the 

 existing state of science, and a thorough examination of any 

 differences that may exist in the more intimate characters of the 

 ovules in hybrid plants is one of our great desiderata. 



"Wichura, however, remarks that the female sexual apparatus 

 suffers in many cases a certain degree of imperfection. The 

 ovaries of certain willows, which appear to be binary hybrids of 

 8. viminalis, alba, and cinerea with S. triandra, or ternary hybrids 

 of 8. viminalis } caprea, and cinerea, are perfectly sterile. They 



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