780 PHYSIOLOGY. 



separated in the different shoots, which present respectively the 

 characters of one or the other of their parents. 



Hybrids rarely produce fertile seeds for many generations, and 

 hence cannot be generally perpetuated with any certainty by 

 them ; if they should be of a woody nature, however, they may 

 be readily propagated by budding, grafting, &c. Hybrids are 

 fertile with the pollen of one of their parents ; the offspring in 

 such a case resembles closely the parent from which the pollen 

 was obtained. By the successive impregnation of hybrids 

 through three, four, or more generations with the pollen of either 

 of their parents, they revert to their original male or female 

 type ; thus, when the hybrid is successively impregnated by the 

 pollen of its male parent, it reverts to the male type ; and when 

 with that of the female, to the female type. The influence of 

 the latter is, however, more gradual. 



Hybrids somewhat rarely occur in wild plants. This arises 

 chiefly from the following causes ; thus, in the first place, the 

 stigma is more likely to be impregnated with the pollen from 

 stamens immediately surrounding it, or from those in other flowers 

 on the same plant, than by that of other and more distant plants ; 

 and, secondly, the stigma has a sort of elective affinity or natural 

 preference for the pollen of its own species. Indeed, Gaertner 

 found, that if the natural pollen and that of another species be 

 applied to the same stigma at the same time, the latter remained 

 inert, and the former alone fecundated the ovules, or was prepo- 

 tent over the other ; and, moreover, that when the natural was 

 applied a short period subsequently to the foreign pollen, the 

 seeds thus produced were never hybrids. Hybrids appear to be 

 produced more frequently in wild plants when the sexes are in 

 separate flowers, and more especially when such flowers are on 

 different plants. 



Hybrids are, however, frequently produced artificially by 

 gardeners applying the pollen of one species to the stigma of 

 another, and in this way, iriiportant and favourable changes are 

 effected in the characters of our flowers, fruits, and vegetables. 

 Such are not, however, commonly true hybrids, but simple cross- 

 breeds. 



Recent investigations would appear to show, that a similar 

 law as regards hybridization occurs in the Cryptogamia as in 

 the Phanerogamia. Thus, Thuret has succeeded in fertilizing 

 the spores of Fucus vesiculosus with the spermatozoids of Fucus 

 serratus, an allied species; but he failed in his attempts to 

 fertilize the spores of one genus of the Melanosporeous Algse by 

 the spermatozoids of another. No other direct evidence has at 

 present been adduced as to the hybridization of Cryptogamous 

 plants, but there can be but little doubt that hybrid Ferns are 

 sometimes produced when a number of species are cultivated 

 together, for it has been noticed that, under such circumstances, 



