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 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.