Many hybrids have no propagative power, while in others it is so far limited as to admit only of reversion to the original specific form. When, a hybrid possesses genera tive power, it breeds more readily with an individual of one of its parent stocks than with another hybrid like itself. The most remarkable example on record of generative power in hybrids is afforded by the experiments of M. Roux of Angoultne, who finds that he can cross hares and rabbits to any extent, and who has thus, by breeding ieporides, established a new and lucrative department in agriculture. For a full account of these experiments, which are well deserving of a trial in this country, the reader may consult Brown-Sequard's Journal de la Physiotogie, vpl. ii. pp. 374-83. These experiments have inflicted a severe blow on the popular doctrine of the permanence of species.
Experiments on the hybridization of plants have been very far from confirming the hybrid origin of forms apparently intermediate between other species, and which were once regarded as probably hybrids produced in a state of nature. The interference of man is usually necessary to effect an intermixture, and in many cases in which it has been found possible, it is by no means of easy aceomplish-nent. The predilection for pollen of the same kind appears to be very strong; and if pollen. both of the same and of another kind, is applied to the stigma of a flower, the result is the same as if its own pollen had been there alone. The hybridizer, therefore, must cut away the stamens of the flower of which the pistil is to be impregnated, and carefully prevent all access of pollen other than that which he brings to it. Even with these precautions, it is found
impossible to produce hybrids between some plants of the same family, and not very dissimilar.
Hybrid plants are said to partake generally of the characters of the male more than of the female parent. It is more certain that. valuable results are often obtained as to siaa and abundance of fruit, brilliancy of flowers, hardiness, and other qualities. The question of the continued fertility of true hybrids is one having most important relations to the great questions concerning species. Some assert that neither among animals nor among plants are hybrids fertile for more than one or two generations, if kept by themselves; although they are readily fertile with either of the parent species, to which they become again assimilated. But this opinion is controverted, and the question must, of course, be dedided by observation of facts, in judging of which, however, questions of no little difficulty must often arise as to what are and what are not different species.
The subject of the hybridization of plants was fl:st investigated, and with great care and very numerous experiments, by Kolrenter, in the end of the 18th c. and has been more recently studied with much attention by Dean Herbert of Manchester, Van Mons, and particularly Gaertner.