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but not invariably, be grafted with ease. But this capacity, as in hybridisation, is by no means absolutely governed by systematic affinity. Although many distinct genera within the same family have been grafted
to- gether,
together,
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
dis- tinct
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 Gärtner found that there was sometimes an innate difference in different individuals
of
of
the same two species in crossing; so
Sagaret
Sageret
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 currant, whereas the currant will take, though with difficulty, on the gooseberry.
We have seen that the sterility of hybrids, which have their reproductive organs in an imperfect condition, is a
very
....
different case from the difficulty of uniting two pure species, which have their reproductive organs perfect; yet these two distinct cases run to a
large
certain
extent parallel. Something analogous occurs in grafting; for Thouin found that three species of Robinia, which seeded freely on their own roots, and which could be grafted with no great difficulty on
a fourth
another
species, when thus grafted were rendered barren. On the other hand, certain species of Sorbus, when grafted on other
species
species,
yielded twice as much fruit as when on their own roots. We are reminded by this latter fact of