566 FUNDAMENTALS OF FRUIT PRODUCTION 



Though these two views differ in details, they agree in the general 

 harmfulness of great differences in the starting season between stock and 

 cion. The very fact that these differences can become harmful is evi- 

 dence against any considerable modification of either stock or cion in 

 season of growth inception. 



In brief, then, the influence of the stock on the season of the cion may 

 be stated, for spring manifestations, in Knight's words: "The graft, or 

 bud, whenever it has become firmly united to the stock, wholly regulates 

 the season and temperature, in which the sap is to be put in motion, in 

 perfect independence of the habits of the stock, whether these be late 

 or early." Concerning the effects on autumnal processes, it may be said 

 that some influences exist but may be obscured by the climate and that 

 they are not necessarily parallel to the nature of the stock. 



Hardiness. — As to the effects of the stock on the hardiness of the cion 

 there is considerable conflict of evidence, due in part, perhaps, to lack 

 of precise definitions. It is frequently stated in European pomological 

 literature that pears on quince stock are much freer from canker than on 

 pear stock. Elsewhere in this work rather strong evidence is cited to 

 show that the common frost canker of Europe is associated with lack of 

 maturity. Evidence presented earlier in this section suggests that cer- 

 tain stocks may affect the season of maturity of the tops. 



Hardiness has been shown to be involved to a great extent with water- 

 retaining capacity which in turn appears to depend in no little degree on 

 maturity. It may be affected by cultural practices and in some cases, 

 apparently, by the stocks used. The stock may, to this extent, be con- 

 sidered to induce hardiness in the top. If, however, the conception of 

 hardiness be that of a specific property which is present or absent there 

 is no evidence that it is transmitted from stock to cion. It is conceivable 

 that a stock may in itself be hardy but through the congeniality of the 

 graft it may actually diminish the hardiness of the cion. 



Fruit growers of the upper Mississippi Valley have a well defined 

 belief that such varieties as Jonathan and Grimes are rendered hardier 

 by topworking on Haas, Oldenburg and similar hardy varieties. It 

 seems plausible that with some varieties there is a certain increase in 

 hardiness due to a slightly earlier maturity; more important, however, 

 is the consideration that the cases under examination are not so much 

 cases of increasing hardiness as they are of substituting a hardy variety 

 in those parts of the tree that are particularly susceptible to winter injury. 

 Even though the hardiness of the cion were not increased in the least, a 

 tree of Jonathan topworked into Oldenburg framework could not help 

 but be hardier, though only within limits. Macoun,^''^ in Canada, top- 

 working such varieties as Baldwin into hardy stocks, was unable to 

 increase the hardiness sufficiently to stand a test winter. 



Hedrick^^ reports that Mahaleb stock makes hardier tops in cherries, 



