290 LAWS GOVERNING THE STEBILTTT 



systematic affinity. Although many distinct genera within 

 the same family have been grafted 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 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 

 species in crossing; so 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 

 different case from the difficulty of uniting two pure spe- 

 cies, 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 re- 

 minded by this latter fact of the extraordinary cases of 

 hippeastrum, passiflora, etc., which seed much more freely 

 when fertilized with the pollen of a distinct species than 

 when fertilized with pollen from the same plant. 



We thus see that, although there is a clear and great dif- 

 ference between the mere adhesion of grafted stocks and 

 the union of the male and female elements in the act of 

 reproduction, yet that there is a rude degree of parallelism 

 in the results of grafting and of crossing distinct species. 

 And as we must look at the curious and complex laws gov- 

 erning the facility with which trees can be grafted on each 



