PRODUCTION OF HYBRIDS. 845 
ing of two varieties of the same species: these may be termed 
sub-hybrids. 
Asa general rule, true hybrids can only be produced between 
nearly allied species, although a few exceptions occur, where 
hybrids have been formed between allied genera ; these are called 
bigeners. The latter, however, are not so permanent as the 
former, for in almost all cases they are short-lived. 
Hybrids always possess some of the'characters of both pa- 
rents, but they generally bear more resemblance to one than the 
other. Sometimes the influence of the male parent is most evi- 
dent, and at other times that of the female, but no law can at 
present be laid down with regard to the kind of influence ex- 
erted by the two parents respectively in determining the cha- 
racters of the hybrid. In very rare cases it has been noticed 
that different shoots of the same hybrid plant have exhibited 
different characters, some bearing flowers and leaves like their 
male parent, others like the female, and some having the cha- 
racters of both. In such cases, therefore, the hybrid characters 
are more or less separated in the different shoots, which present 
respectively the characters of one or the other of their parents. 
An example of these facts may be seen in Cytisus Adami, pro- 
duced by the true hybridation of Cytisus Laburnuwm and Cytisus 
purpureus. 
Hybrids rarely produce fertile seeds for many generations, 
and hence cannot be generally perpetuated with any certainty 
by them; but if they are of a woody nature, they may be 
readily propagated by budding, grafting, and other analogous 
processes. (See page 107.) 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 re- 
vert 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, how- 
ever, 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 dis- 
tant 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 prepotent over the other; and, moreover, 
that when the natural was applied a short period subsequently 
