CONTRIBUTIONS FROM THE WISLEY LABORATORY. 501 



Frequently, too, the dead tissue of the spot drops out and leaves a hole 

 in the leaf, in the same way as the tissue killed by the ' shot-hole ' 

 fungus in peaches. In very bad cases the leaves themselves drop pre- 

 maturely, so that a branch may become defoliated for a great part of 

 its length. The first indication of the attack is the appearance of a 

 purplish tinge on the affected area. 



The part of the tree most usually affected in the past year was the first 

 9 to 12 inches of the growth made in the early part of the season, but 

 later on in the autumn it frequently happened that the greater part of 

 the foliage became more or less affected. 



The Injury to the Trees.— As all the food upon which the tree depends 

 for its existence and growth is made in the green leaves, and there 



only, it is obvious that anything that interferes to the destruction of 

 the tissues of these organs, reducing their effective area, must seriously 

 handicap the tree, not only in the season of the attack, but also in those 

 immediately following. For in each season a certain amount of the food 

 made in the leaves is sent into the stem, where it forms a reserve of food 

 to serve for the start of growth in the next year, and upon this reserve 

 depends to a large extent the power of the tree to withstand adverse 

 conditions during the early part of the growing season ; and the same 

 factor largely determines the weight of fruit that may be borne without 

 materially weakening the tree. When the attack follows weakening from 

 any other cause, the result may be little short of disastrous. In the train 

 of such reduction of effective leaf area, particularly if the attack be 

 recurrent, must come lessened vitality, inability to recoup losses due 

 to the attacks of aphides and other insects, lessened crops (though, 



