92 



UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



In ungrafted vines this exchange takes place readily and all the 

 branches and all the roots are well nourished. In grafted vines, owing 

 to the fact that the stock and scion are of different species and, there- 

 fore, of different structure and composition, there is some interference 

 with the exchange, resulting in a slight weakening of the whole vine. 

 This weakening, under proper conditions, is so slight that it does not 



FIG. 1. Showing effect on Resistant Stock of allowing the scion roots to remain. 

 (Redrawn after Viala and Ravaz.) 



A. Old grafted vine with large top roots (S) from scion. Note small, weak resistant stock (R). 



B. Normal grafted vine on which no scion roots have been allowed to develop. Note smooth 



union (U) and strong resistant stock (R). 



detract from the usefulness of the vine, and, in fact, like many other 

 slightly weakening causes, it usually has the effect of producing an 

 increased tendency to fruitfulness. If, however, the scion is allowed to 

 make its own roots, the return stream of nutritive material takes the 

 course of least resistance and goes principally into the scion roots. The 

 result is that these grow vigorously, so long as the phylloxera is absent, 

 and the roots of the resistant stock are starved and finally die. This 



