GRAFT-HYBRIDS AND OTHER CA1MERAS 383 



Modification of One Graft-symbiont by the Other. The repressing 

 or stimulating effects of certain scions on certain stocks is well known. 

 Excellent examples are found in the various "dwarf" rootstocks used in 

 the culture of the pome and citrous fruits. Besides the dwarfing effect 

 of the stock upon the scion, there is often a reciprocal stimulating effect 

 of the scion upon the stock which causes the latter to increase in diameter 

 faster than the scion. A mutually stimulating effect is sometimes ob- 

 served, as in the almond and the peach when used as graft components. 

 The importance of selecting stock of about the same vigor, when grafted, 

 as the scion has long been recognized by nurserymen. The fact that 

 grafts usually exhibit a certain amount of modification according to the 

 kind of stock used has given rise to many reputed cases of deleterious 

 effects and extreme modifications due to grafting. 



A matter of considerable economic importance involving this question 

 concerns the culture of wine grapes. After the introduction of American 

 vines and their hybrids into the phylloxera-infested districts of France 

 there was widespread concern over the possibility that the quality of the 

 French wines would be injured by grafting on the new stocks. Many 

 investigations were carried on. Although in the earlier stages of the 

 work some very definite effects of stock on scion were reported, the 

 evidence as a whole is considered by leading investigators as indicating 

 merely that the stock may either increase or decrease the capacity of the 

 scion according to the combination used. It has been concluded that 

 where due account is taken of affinity of stock and scion, if other condi- 

 tions are favorable, grafting has caused no deleterious effect on yield or 

 quality. 



A specific case of supposed deleterious effects attributed to the in- 

 fluence of stock on scion was observed by Paelinck. A dark-red variety 

 of cherry, Early Rivers, was grafted on mahaleb stock. The resulting 

 tree bore fruit which was yellowish white in color, of smaller size and 

 which matured 8 days later than Early Rivers. Scions from this white- 

 fruited tree were grafted on mazzard stock which has small black fruit 

 "to see whether the white fruits would revert to the dark color." The 

 result as one would expect was negative. Undoubtedly this was a case 

 of bud mutation. 



Other reputed extreme effects of graf t-symbionts involve the supposed 

 transfer of characters from the one to the other. Baur asserts that after 

 reviewing the accounts of many grafting experiments he has reached 

 the conclusion that most of the reciprocal effects between stock and 

 scion can be explained on the basis of modification in nourishment. 

 Moreover, where this explanation does not hold there is a more probable 

 cause than the notion of transfer of characters. For example, in the case 

 of Daniel's eggplant which, when grafted on tomato bore tomato-shaped 



