226 ON THE ORIGIN OF SPECIES 



of Pelargonium, Fuchsia, Calceolaria, Petunia, Rhodo- 

 dendron, etc., have been crossed, yet many of these 

 hybrids seed freely. For instance, Herbert asserts that 

 a hybrid from Calceolaria integrifolia and plantaginea, 

 species most widely dissimilar in general habit, ' re- 

 produced itself as perfectly as if it had been a natural 

 species from the mountains of Chile.' 1 have taken 

 some pains to ascertain the degree of fertility of some 

 of the complex crosses of Rhododendrons, and I am 

 assured that many of them are perfectly fertile. Mr. 

 C. Noble, for instance, informs me that he raises stocks 

 for grafting from a hybrid between Rhod. Ponticum 

 and Catawbiense, and that this hybrid ' seeds as freely 

 as it is possible to imagine.' Had hybrids, when fairly 

 treated, gone on decreasing in fertility in each suc- 

 cessive 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 individuals of the same hybrid variety are 

 allowed to freely cross with each other, and the in- 

 jurious influence of close interbreeding is thus pre- 

 vented. 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 pollen, 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 con- 

 sidered 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 



