and although both the ovules and pollen of the same flower were
perfectly good with respect to other species, yet as they were
functionally imperfect in their mutual self-action, we must infer that
the plants were in an unnatural state. Nevertheless these facts show on
what slight and mysterious causes the lesser or greater fertility of
species when crossed, in comparison with the same species when
self-fertilised, 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, Rhododendron, 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, reproduced itself as perfectly as if it
had been a natural species from the mountains of Chile. 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 Rhododendron 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 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 individuals 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 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 considered
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