8 HYBRIDISM. [Chap. IX. 



a hybrid from Calceolaria integrifolia and plantaginea, 

 species most widely dissimilar in general habit, " re- 

 produces itself as perfectly as if it had been a natural 

 species from the mountains of Chili." I have taken 

 some pains to ascertain the degree of fertility of some 

 of the complex crosses of Ehododendrons, and I am 

 assured that many of them are perfectly fertile. Mr. 

 C. ISToble, 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, always gone on decreasing in fertility in each 

 successive generation, as Gartner believed to be the 

 case, the fact would have been notorious to nursery- 

 men. Horticulturists raise large beds of the same hy- 

 brid, and such alone are fairly treated, for by insect 

 agency the several individuals are allowed to cross freely 

 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 hy- 

 brid Rhododendrons, which produce no pollen, fof 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 

 distinct in the scale of nature can be crossed more easily 

 than in the case of plants; but the hybrids themselves 

 are, I think, more sterile. It should, however, be borne 

 in mind that, owing to few animals breeding freely under 



