HYBRIDISM 11 



elements in hybrid plants are already affected in some 

 degree. But I believe that their fertility has been dimin- 

 ished in nearly all these cases by an independent cause; 

 namely, by too close interbreeding. I have made so 

 many experiments and collected so many facts, showing 

 on the one hand that an occasional cross with a distinct 

 individual or variety increases the vigor and fertility of 

 the offspring, and on the other hand that very close in- 

 terbreeding lessens their vigor and fertility, that I cannot 

 doubt the correctness of this conclusion. Hybrids are 

 seldom raised by experimentalists in great numbers; and 

 as the parent-species, or other allied hybrids, generally 

 grow in the same garden, the visits of insects must be 

 carefully prevented during the flowering season: hence 

 hybrids, if left to themselves, will generally be fertilized 

 during each generation by pollen from the same flower; 

 and this would probably be injurious to their fertility, 

 already lessened by their hybrid origin. I am strength- 

 ened in this conviction by a remarkable statement re- 

 peatedly made by Gartner, namely, that if even the less 

 fertile hybrids be artificially fertilized with hybrid pollen 

 of the same kind, their fertility, notwithstanding the fre- 

 quent ill effects from manipulation, sometimes decidedly 

 increases, and goes on increasing. Now, in the process of 

 artificial fertilization, pollen is as often taken by chance 

 (as I know from my own experience) from the anthers of 

 another flower as from the anthers of the flower itself 

 which is to be fertilized; so that a cross between two 

 flowers, though probably often on the same plant, would 

 be thus effected. Moreover, whenever complicated experi- 

 ments are in progress, so careful an observer as Gartner 

 [would have castrated his hybrids, and this would have 



