CITRUS CULTURE IN PORTO RICO 



23 



Decay may set m before the scars heal, continue into the trunk, and 

 eventually cause the death of the tree. The root growth of such trees 

 is frequently too slow to permit the sap to reach the leaves rapidly 

 enough to prevent wilting, especially when the air is dry and moving 

 fast. 



The value of wind protection for young trees is mainly that of 

 maintaining a humid atmosphere. With the checking of excessive 

 air movement the tree may survive under conditions which would 

 make growth impossible without wind protection. The checking of 

 excessive air movement also promotes the growth of beneficial fungi. 



Figure 14. — Two-year-old tree which was planted on mound. 

 The mound has practically disappeared and the crown 



roots are exposed 



This was noted in the groves first planted on the island. Most of 

 the trees in these groves were severely attacked by the purple scale, 

 which was not kept in check by beneficial fungi until after wind pro- 

 tection was established. Nowadays newly planted trees which are 

 similarly exposed do not suffer from scale to such an extent, because 

 the beneficial fungi, especially the red-headed fungus (Sphcerostilbe 

 coccophila ) , seem to be able to maintain themselves under more ad- 

 verse conditions than formerly. Planting tall-growing plants for 

 cover crops among the young trees has nevertheless proved to be a 

 most economical and time-saving practice in the establishment of 

 citrus plantations. Under this practice cultivation during the first 

 few years consists in plowing under as soon as it matures each crop of 



