HYBEIDISM. 
Chap. VIII. 
252 
are perfectly fertile. Mr. C. NoHe^ for instancej informs 
me that he raises stocks for grafting from a hybrid 
between Ehod. Ponticnm and Catawbiense^ and that 
this hybrid seeds as freely as it is possible to ima¬ 
gine.’' Had hybrids^ when fairly treated^ gone on de¬ 
creasing in fertility in each successive 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 indi¬ 
viduals of the same hybrid variety are allowed to freely 
cross 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 rhododendrons, which produce no pollen, 
for he will And 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 
considered 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 
has been crossed with 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 be¬ 
tween them and the canary, or that their hybrids. 
