318 EXPERIMENTS WITH PLANTS 



In order to increase the production of fruit, various 

 methods are employed. The best method is to increase 

 the vigor of the tree by good tilth and occasional 

 application of fertilizers. In applying fertilizers, it is 

 to be noted that nitrogen tends to produce vegetative 

 growth at the expense of fruit, while phosphoric acid 

 tends rather to produce fruit (this effect of phosphoric 

 acid has been demonstrated in some cases but not 

 generally) : potash is probably the most necessary 

 fertilizer for orchards. 



If the growth is so vigorous that the tree produces 

 wood at the expense of fruit, this tendency may 

 be checked by seeding down for a time, decreasing 

 the amount of tillage and using mineral rather than 

 nitrogenous fertilizers. 



A local check is often applied, in the case of a 

 branch which does not bear, by ringing or girdling. 

 This varies in degree from simply running a knife 

 around the branch near its base to removing a strip 

 of bark from one to several inches wide (see p. 257), 

 or simply by cutting a notch. 



Partially cutting off the water supply by bending, 

 twisting, breaking or notching the branch often causes 

 it to bear. In bending the branch, it is turned down- 

 ward and fastened in that position. This method is 

 used most frequently for Grapes and fruit trees trained 

 against walls. Twisting acts like bending but more 

 energetically ; the branch is twisted half-way round ; 



