238 DEGREES OF STEKILITY. Chat. VIII. 



freely as it is possible to imac^ine." Had liybrids, when fairly 

 treated, always p^ono on decreasing in fertility in each succes- 

 sive generation, as Gartner believed to be the case, the fact 

 would have been notorious to nursery-men. Horticulturists 

 raise large beds of the same hybrids, and such alone are fairly 

 treated, for by insect-agency the several individuals of the 

 same hybrid variety are allowed to freely cross with each other, 

 and the injurious influence of close interbreeding is thus ]irc- 

 vented. Any one may readily convince himself of the eih- 

 ciency of insect-agency by examining the lloAvers 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 jilants. If our systematic arrange- 

 ments 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 ; 

 l)ut the hybrids themselves are, I think, more sterile. 1 doubt 

 whether any case of a perfectly-fertile hybrid animal can be 

 considered as thoroughly well authenticated. It should, how- 

 ever, 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 Avith 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 between them and the canary, or that their Inbrids, 

 should be perfectly fertile. Again, with resjiect to the fertility 

 in successive generations of the more fertile hybrid animals, 

 1 hardly know of an instance in which two fiimilies of the same 

 hyl>rid have been raised at the same time from difierent par- 

 ents, so as to avoid the ill-effects of close interbreeding. On 

 the contrary, brothers and sisters have usually been crossed 

 in each STiccessive generation, in opposition to the constantly- 

 repeated admonition of every breeder. And in this case, it is 

 not at all surprising that the inherent sterility in the hybrids 

 should have gone on increasing. If we were to act thus, and 

 pair brothers and sisters in the case of any pure animal, which 

 from any cause had the least tendency to sterility, the breed 

 would assuredly be lost in a few generations. 



Although I do not know of any thoroughly well-autlienli- 

 catcd cases of perfectly-fertile liybrid animals, I have reason to 



