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 species 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 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 different case from the difficulty
of uniting two pure species, which have their reproductive organs perfect;
yet these two distinct classes of cases run to a large 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 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 cases of
Hippeastrum, Passiflora, etc.
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