222 HYBRIDISM. [CHAP. IX. 



showing on the one hand that an occasional cross with a distinct 

 individual or variety increases the vigour and fertility of the 

 offspring, and on the other hand that very close interbreeding 

 lessens their vigour and fertility, that I cannot doubt the correct- 

 ness of this conclusion. Hybrids are seldom raised by experi- 

 mentalists 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 fertilised 

 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 strengthened in this conviction by a 

 remarkable statement repeatedly made by Gartner, namely, that 

 if even the less fertile hybrids be artificially fertilised with hybrid 

 pollen of the same kind, their fertility, notwithstanding the 

 frequent ill effects from manipulation, sometimes decidedly 

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

 artificial fertilisation, 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 

 fertilised ; so that a cross between two flowers, though probably 

 often on the same plant, would be thus effected. Moreover, 

 whenever complicated experiments are in progress, so careful an 

 observer as Gartner would have castrated his hybrids, and this 

 would have ensured in each generation a cross with pollen from 

 a distinct flower, either from the same plant or from another plant 

 of the same hybrid nature. And thus, the strange fact of an 

 increase of fertility in the successive generations of artificially 

 fertilised hybrids, in contrast with those spontaneously self-fer- 

 tilised, may, as I believe, be accounted for by too close inter- 

 breeding having been avoided. 



Now let us turn to the results arrived at by a third most 

 experienced hybridiser, namely, the Hon. and Eev. W. Herbert. 

 He is as emphatic in his conclusion that some hybrids are perfectly 

 fertile as fertile as the pure parent-species as are Kol renter and 

 Gartner that some degree of sterility between distinct species is a 

 universal law of nature. He experimented on some of the very 

 same species as did Gartner. The difference in their results may, 

 I think, be in part accounted for by Herbert's great horticultural 

 skill, and by his having hot-houses at his command. Of his many 

 important statements I will here give only a single one as an 

 example, namely, that " every ovule in a pod of Crinurn capense 

 fertilised by C. revolutum produced a plant, which I never saw to 

 occur in a case of its natural fecundation." So that here we have 

 perfect or even more than commonly perfect fertility, in a first 

 cross between two distinct species. 





