066 . THE AMERICAN NATURALIST [Vol. LIII 



been rather conventionally and very loosely assumed that 

 reciprocal crosses are invariably identical in type. That 

 such is not necessarily the case, Darwin's early observa- 

 tions should suffice to indicate. 



The problem of the fertility of selfed and crossed 

 plants engaged Darwin's close interest in forty-one cases 

 belonging to tw^enty-three species. The ratio of the fer- 

 tility of the crossed to that of the self -fertilized plants was 

 found to be as 100 : 60. In another experiment to deter- 

 mine the relative fertility of flowers when crossed or 

 selfed, the ratio in thirty cases belonging to twenty-seven 

 species was as 100:55. 



There is no evidence, Darwin finds, That the fertility of plants goes 



correspondence, either in the parent plants or in the successive genera- 

 tions, between the relative number of seeds produced by the crossed 

 and self -fertilized flowers, and the relative powers of growth of the 

 seedlings raised from such seeds (lb, 327). 



Darwin's investigations were directed quite extensively 

 to the question of self-fertility in plants, a field w^hich 

 bears strongly upon our knowledge of heredity, but in 

 which likewise comparatively little experimental work 

 has been done since his time. As the result of his own 

 studies, supplemented by those of Hildebrand and Fritz 

 Miiller, he was able to say: 



We may therefore confidently assert, that a self-sterile plant can be 



l^ogarding the cause of sterility or inability to accept 

 fertilization, wo arc as irrcatlv at a loss for an explanation 



