283 STBRIDtsM. 



causes the lesser or greater fertility of a species sometimes 

 depends. 



The practical experiments of horticulturists, though not 

 made with scientific precision, deserve some notice. It is 

 notorious in how complicated a manner the species of 

 Pelargonium, Fuchsia, Calceolaria, Petunia, Ehododen- 

 dron, etc., have been crossed, yet many of these hybrids 

 seed freely. For instance, Herbert asserts that a hybrid 

 from Calceolaria integrifolia and plantaginea, sjjecies most 

 widely dissimilar in general habit, "reproduces itself as 

 perfectly as if it had been a natural species from the 

 mountains of Chili." I have taken some pains to ascer- 

 tain 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, 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 hybrid, 

 and such alone are fairly treated, for by insect agency the 

 several individuals are allowed to cross fi-eely 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 Rliododendrons, which 

 produce no pollen, for he will find on their stigmas plenty 

 of pollen brought from other flowers. 



In regard to auim'als, much fewer experiments have been 

 carefully tried than with plants. If our systematic arrange- 

 ments can be trusted, that is, if the genera of animals are 

 as distinct from each others 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 confinement, few experiments have been fairly 

 tried: for instance, the canary-bird has been crossed with 

 nine distinct species of finches, but, as not one of these 



