INFLUENCE OF CION AND STOCK. 77 



the quince. Downing asserts that some varieties "are 

 considerably improved in flavor" by working upon quince. 

 Similar results may occur in the dwarfing of apples. 



A favorite illustration in support of the reciprocal influ- 

 ences of stock and cion is the fact of transfer of color or 

 variegation by grafting. Darwin called attention to this 

 phenomenon, and used the term "graft-hybrid" to desig- 

 nate similar mongrel offspring of certain unions. But this 

 class of phenomena seems to follow inoculation rather 

 than grafting per se. The transferable nature of variega- 

 tion is well known in certain species, but it is entirely 

 inexplicable in the present state of our knowledge ; it 

 seems certain, however, that it does not merit attention 

 under a discussion of grafting. So long ago as 1727 vari- 

 egation was designated by Bradley a "distemper," which 

 "may be communicated to every plant of the same tribe 

 by inoculating only a single bud." In our own day, Morren 

 has called it the "contagion of variegation." 



The above outline illustrates the fact that the results 

 of graftage are profoundly modified by conditions. Ad- 

 verse conditions must give unsatisfactory results, and may 

 lead to a premature denunciation of the whole system of 

 propagation upon the roots of other plants. But, on the 

 other hand, proper conditions and good execution afford 

 abundant and positive proof that graftage is essential to 

 best success in many departments of horticulture. 



Limits of Graftage.— Probably all exogenous plants — 

 those which possess a distinct bark and pith — can be 

 grafted. Plants must be more or less closely related to each 

 other to allow of successful graftage of the one upon the 

 other. What the affinities are in any case can be known 

 only by experiment. As a rule, plants of close botanical 

 relationship, especially those of the same genus, graft upon 

 each other with more or less ease ; yet this relationship is 

 by no means a safe guide. A plant will often thrive better 

 upon a species of another genus than upon a congener. 

 The pear, for instance, does better upon many thorns than 



