DISEASES 95 



the leaf, fruit or branch. As a rule, the leaves and fruits 

 which are attacked have a tendency to drop from the tree. 

 The general treatment for these Diseases is to spray with 

 some fungicidal mixture, like the Bordeaux mixture or the 

 ammoniacal carbonate of copper. The treatment is useful 

 in proportion as it is applied early and thoroughly. After 

 the fungus once gets into the tissues of the host-plant, it is 

 difficult, if not impossible, to kill it. If, however, the fungi- 

 cide is upon the plant before the fungus is, the parasite 

 may not be able to obtain a foothold. Even after it does 

 obtain a foothold, it is probable, however, that the spray 

 will check its spread by preventing the development of its 

 external parts. 



(2) The physiological and bacterial Diseases, or those 

 which are termed constitutional troubles. In these cases 

 there are rarely any definite spots, as in the attacks of 

 parasitic fungi, but the entire leaf, or even the entire plant, 

 or a large part of it, shows a general weakening and Dis- 

 ease, as if there were some cutting off of the accustomed 

 source of nourishment. Such Diseases are very likely to be 

 seen in a general yellowing and death of the leaf, in the 

 dying of the leaf along the main veins and around the 

 edges, showing that the difficulty is one which affects the 

 entire leaf, and not any particular part of it. In general, 

 there is a tendency for the foliage in plants so attacked to 

 wither up and hang on the tree for a time. The peach- 

 yellows and pear blight are Diseases of this kind. There 

 are no specific treatments for troubles of this sort. They 

 must be approached by what physicians call prophylaxis 

 that is, by methods of sanitation and prevention. The dis- 

 eased plants or parts are cut away and burned. All those 

 conditions which seem to favor the development of the Dis- 

 ease are removed. Varieties which are particularly sus- 

 ceptible are discarded. Careful management in matters of 

 this sort is often much more important than any attempt at 

 specific treatment. 



