DEGREES OF STERILITY 303 



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 Pelar- 

 gonium, Fuchsia, Calceolaria, Petunia, Rhododendron, &c., 

 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, "reproduces 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 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 freely with each other, and 

 the injurious influence of close interbreeding is thus pre- 

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

 ency 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 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 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 breeds freely in confinement, we have no right to 

 expect that the first crosses between them and the canary, 



