THE RECIPROCAL INFLUENCES OF STOCK AND CION 579 



Sometimes grafting has opposite effects. Without specifying as to 

 the effect on fruitfulness, Jost records that Pistacia vera (the pistachio 

 nut) as a seedUng Uves at the most 150 years, on P. lentiscus only 40, while 

 on P. terehenthinus it reaches 200 years. 



General Influence of Stock on Cion. — Such evidence as is available 

 on the influence of stock on cion has been presented. This influence 

 wherever it is positive, is, almost without exception, quantitative. There 

 is no doubt of the influence of stock on vigor and form of growth; there 

 seems httle reason to doubt some influence of the stock on the termination 

 of the growing season, which is, after all, only a phase of vigor. If, now, 

 the effect of stock on vigor be accepted, all other influences of stock on 

 cion can be explained through that one influence. None of these influ- 

 ences differs from effects that might be secured from so manipulating 

 cultural conditions as to modify vigor. Cultural conditions can be 

 changed to induce early fruiting or late growth or earlier ripening or 

 hardiness or disease resistance or increased fruit-bud formation or better 

 setting of fruit or larger or better ripened fruits. Girdling the grape 

 will increase the sugar content and size of the fruit. The dwarfed trees 

 of China that bear inferior undeveloped fruit are on their own roots j^"" 

 the inferiority of the fruit is brought about by manipulation, not by any 

 influence of stock on cion. 



The influence of the stock on cion is not to be minimized; much 

 harm has come from ignoring it. Frequently it is of extreme importance. 

 However, it is important to the cion only as its vigor is important to the 

 cion and as the graft union is satisfactory; the cion, for adjustment to one 

 locality or purpose, may require a vigorous stock; for adjustment to 

 another locality or purpose it may require a less vigorous stock or one 

 that thrives in a soil of peculiar character. Adjustment of stock to cion, 

 then, should be made with these factors in mind. In addition, the choice 

 of stock should, where choice is possible, be made with soil, pests and 

 cultural practices in view; conversely these should be considered in their 

 relation to the stock as well as to the top. 



INFLUENCE OF CION ON STOCK 



Instances of apparent influence of cion on stock are more striking in 

 plants other than those grown for their fruit, possibly because the 

 interest of the fruit grower is centered chiefly in the cion and minor influ- 

 ences on the stock are less likely to attract attention. Furthermore, an 

 influence of cion on stock might involve a reaction on the cion and so 

 be attributed to the effect of stock on cion. However, a few cases, some 

 undoubted and some less clearly defined, are available for consideration. 



Just as among the influences of the stock on the cion, the effect on 

 vigor and form of the cion are the most obvious, possibly because most 



