262 
HYBKIDISM. 
Chap. VIII. 
gether, in other cases species of the same genus will 
not take on each other. The pear can be grafted far 
more readily on the quince, which is ranked as a distinct 
genus, than on the apple, which is a member of the 
same genus. Even different varieties of the pear take 
with different degrees of facility on the quince; so do 
different varieties of the apricot and peach on certain 
varieties of the plum. 
As Gartner found that there was sometimes an innate 
difference in different individuals of the same two spe¬ 
cies in crossing; so Sagaret believes this to be the case 
with different individuals of the same two species in 
being grafted together. As in reciprocal crosses, the 
facility of effecting an union is often very far from 
equal, so it sometimes is in grafting; the common 
gooseberry, for instance, cannot be grafted on the cur¬ 
rant, whereas the currant will take, though with diffi¬ 
culty, on the gooseberry. 
We have seen that the sterility of hybrids, which 
have their reproductive organs in an imperfect con¬ 
dition, is a very different case from the difficulty of 
uniting two pure species, which have their reproduce 
tive organs perfect; yet these two distinct cases run 
to a certain extent parallel. Something analogous 
occurs in grafting; for Thouin found that three species 
of Eobinia, which seeded freely on their own roots, 
and which could be grafted with no great difficulty 
on another species, when thus grafted were rendered 
barren. On the other hand, certain species of Sorbus, 
when grafted on other species, yielded twice as much 
fruit as when on their own roots. We are reminded by 
this latter fact of the extraordinary case of Hippe- 
astrum. Lobelia, &c., which seeded much more freely 
when fertilised with the pollen of distinct species, than 
when self-fertilised with their own pollen. 
