They are of mixed origin

Usage examples of hybrids.

Although I do not know of any thoroughly well-authenticated cases of perfectly fertile hybrid animals, I have some reason to believe that the hybrids from Cervulus vaginalis and Reevesii, and from Phasianus colchicus with P.

I am strengthened in this conviction by a remarkable statement repeatedly made by Gartner, namely, that if even the less fertile hybrids be artificially fertilised with hybrid pollen of the same kind, their fertility, notwithstanding the frequent ill effects of manipulation, sometimes decidedly increases, and goes on increasing.

Moreover, whenever complicated experiments are in progress, so careful an observer as Gartner would have castrated his hybrids, and this would have insured in each generation a cross with the pollen from a distinct flower, either from the same plant or from another plant of the same hybrid nature.

He is as emphatic in his conclusion that some hybrids are perfectly fertile--as fertile as the pure parent-species--as are Kolreuter and Gartner that some degree of sterility between distinct species is a universal law of nature.

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.

On the other hand, the resemblance in mongrels and in hybrids to their respective parents, more especially in hybrids produced from nearly related species, follows according to Gartner the same laws.

Pacific Ocean, faunas of Paley, on no organ formed to give pain Pallas, on the fertility of the wild stocks of domestic animals Paraguay, cattle destroyed by flies Parasites Partridge, dirt on feet Parts greatly developed, variable, degrees of utility of Parus major Passiflora Peaches in United States Pear, grafts of Pelargonium, flowers of, sterility of Peloria Pelvis of women Period, glacial Petrels, habits of Phasianus, fertility of hybrids Pheasant, young, wild Pictet, Prof.

Chapter VIII Hybridism Distinction between the sterility of first crosses and of Hybrids -- Sterility various in degree, not universal, affected by close interbreeding, removed by domestication -- Laws governing the sterility of Hybrids -- Sterility not a special endowment, but incidental on other differences -- Causes of the sterility of first crosses and of Hybrids -- Parallelism between the effects of changed conditions of life and crossing -- Fertility of varieties when crossed and of their mongrel offspring not universal -- Hybrids and mongrels compared independently of their fertility -- Summary.

Lastly, the hybrids or mongrels from between all the domestic breeds of pigeons are perfectly fertile.

We see this tendency to become striped most strongly displayed in hybrids from between several of the most distinct species.

The importance of the fact that hybrids are very generally sterile, has, I think, been much underrated by some late writers.

On the theory of natural selection the case is especially important, inasmuch as the sterility of hybrids could not possibly be of any advantage to them, and therefore could not have been acquired by the continued preservation of successive profitable degrees of sterility.

Gartner was enabled to rear some hybrids, carefully guarding them from a cross with either pure parent, for six or seven, and in one case for ten generations, yet he asserts positively that their fertility never increased, but generally greatly decreased.

And thus, the strange fact of the increase of fertility in the successive generations of artificially fertilised hybrids may, I believe, be accounted for by close interbreeding having been avoided.

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.