280 HYBRIDISM. 



spect to this decrease, it may first be noticed that when 

 any deviation in structure or constitution is common to 

 both parents, this is often transmitted in an augmented 

 degree to the offspring; and both sexual elements in hybrid 

 plants are already affected in some degree. But I believe 

 that their fertility has been diminished in nearly all these 

 cases by an independent cause, namely, by too close inter- 

 breeding. 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 interbreeding lessens their vigor and fertil- 

 ity, that I can not 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 fer- 

 tilized during each generation by pollen from the same 

 flower; and this would probably be injurious to their fertil- 

 ity, already lessened by their hybrid origin. I am 

 strengthened in this conviction by a remarkable statement 

 repeatedly 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 flow- 

 ers, 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 in- 

 sured in each generation a cross with pollen from a dis- 

 tinct flower, either from the same jDlant or from another 

 plant of the same hybrid nature. And thus, the strange 

 fact of an increase of fertility in the successive generations 

 of artificAciUy fertilized hybrids, in contrast with those spon- 

 taneously self-fertilized, may, as I believe, be accounted 

 for by too close interbreeding having been avoided. 



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