CiiAi-. Vin. OF FIRST CROSSPIS AND OF HYBRIDS. o|5 



species, can usually, but not iuvariabl}', be grafted with case, 

 liut this capacity, as in hybridization, is by no means absolute- 

 ly jToverned by systematic allinity. Althoup^'h many distinct 

 genera within the same family have been grafted together, in 

 otiier cases species of the same genus will not take on each 

 other. The j)ear can be grafted far more readily on the 

 rpiince, which is ranked as a distinct genus, than on the apple, 

 wliich is a member of the same genus. Even dilferent varieties 

 of the pear take with different degrees of facility on the 

 quince ; so do dilTerent varieties of the apricot and peach on 

 certain varieties of the plum. 



As Gartner found that there was sometimes an innate dif- 

 ference in dilferent individuals of the same two species in 

 crossing ; so Sageret behoves this to be the case with different 

 individuals of the same two species in being grafted together. 

 As in recipi-ocal crosses, the facility of effecting a union is 

 often very far from equal, so it sometimes is in grafting; the 

 couimon gooseberry, for instance, cannot be grafted on tlie cur- 

 rant, Avhereas the currant will take, though with difficulty on 

 the gooseberry. 



AVe have seen that the sterility of hybrids, which have 

 their reproductive organs in an imperfect condition, is a differ- 

 ent case from the dilHculty 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 llo- 

 bini;i, which seeded freely on their own roots, and which could 

 bo grafted with no great difficulty on another species, when 

 thus grafted were rendered barren. On the otiier hand, cer- 

 tain species of Sorbus, when grafted on other species, yielded 

 twice as much fruit as Avhen on their own roots. AVe are re- 

 minded by this latter fact of the extraordinary cases of Ilip- 

 jieastrum, Passillora, etc., which seed much more freely wIkmi 

 fertilized with the ])ollen of a distinct species, than wIk.mi fer- 

 tilized with }K)llen from tlie same plant. 



Wc thus see, that, althougli 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 reproduc- 

 tion, yet that there is a rude degree of parallelism in the re- 

 sults of grafting and of crossing distinct species. And as wc 

 must look at the curious and complex laws governing the 

 facility with which tre(\s can be grafted on each other as inci- 

 dental on unknown differences in their vegetative SA'stcms, so 



