252 HYBRIDISM. Chap. VIII. 



between Khod. Ponticum and Catawbiense, and that 

 this hybrid "seeds as freely as it is possible to ima- 

 gine." Had hybrids, when fairly treated, gone on de- 

 creasing in fertility in each successive generation, as 

 Gartner believes to be the case, the fact would have 

 been notorious to nurserymen. Horticulturists raise 

 large beds of the same hybrids, and such alone are 

 fairly treated, for by insect agency the several indi- 

 viduals of the same hybrid variety are allowed to freely 

 cross with each other, and the injurious influence of 

 close interbreeding is thus prevented. Any one may 

 readily convince himself of the efficiency of insect- 

 agency by examining the flowers of the more sterile 

 kinds of hybrid rhododendrons, which produce no pol- 

 len, for he will find on their stigmas plenty of pollen 

 brought from other flowers. 



In regard to animals, much fewer experiments have 

 been carefully tried than with plants. If our systematic 

 arrangements can be trusted, that is if the genera of 

 animals are as distinct from each other, as are the genera 

 of plants, then we may infer that animals more widely 

 separated in the scale of nature can be more easily 

 crossed than in the case of plants ; but the hybrids 

 themselves are, I think, more sterile. I doubt whether 

 any case of a perfectly fertile hybrid animal can be 

 considered as thoroughly well authenticated. It should, 

 however, be borne in mind that, owing to few animals 

 breeding freely under confinement, few experiments 

 have been fairly tried: for instance, the canary-bird 

 has been crossed with nine other finches, but as not 

 one of these nine species breeds freely in confinement, 

 we have no right to expect that the first crosses be- 

 tween them and the canary, or that their hybrids, 

 should be perfectly fertile. Again, with respect to the 

 fertility in successive generations of the more fertile 



