HYBRIDISM 235 



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 varie- 

 ties 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 con- 

 dition, 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 

 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 

 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, etc., which seeded much more freely 

 when fertilised with the pollen of distinct species, than 

 when self-fertilised with their own pollen. 



We thus see, that although there is a clear and 

 fundamental difference 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 



