32 Disease and Death of Trees — Generalities 



Nevertheless, since different parts are interdependent 

 for their nutrition, any interference in feeding arrangements 

 will be more or less felt, at least in all growing parts which 

 organically belong together. It is, therefore, usually, one 

 side of the crown, in sympathy with the same side of the root 

 system, which is diseased or dead, while the other side may 

 remain alive and even ^^gorous. 



This fact, together with the ability of trees to replace lost 

 parts, makes it possible to resuscitate and restore quite 

 dilapidated specimens by surgery and proper treatment, 

 and to prolong their life almost indefinitely. 



General Causes of Disease. There are two general causes 

 of disease, namely, unfavorable environment and parasitic 

 organisms (which, however, should really be considered a 

 part of the en\dronment) . Under the influence of these 

 two we may group for diagnosis and treatment four classes 

 of troubles to which trees are exposed, namely: physiolog- 

 ical diseases which are produced by generally unfavorable 

 conditions of growth in atmosphere, cHmate, or season, and 

 soil; mechanical injuries, which destroy living parts or else 

 weaken the dead wood of the body; attacks of fungi and 

 other plants; and attacks of insects. 



Usually several of these causes work together or are even 

 interdependent, and it is not always easy to tell which is the 

 primary, which the secondary, cause of the diseased or abnor- 

 mal condition. This difficulty of diagnosis is especially 

 experienced when there are no visible signs of insect or fungus 

 pests present and when the trouble seems not localized but 

 exhibits itself in general debihty or sickly appearance. 



Fungus attacks are usually secondary results of mechan- 

 ical injuries, and insect pests become in most cases fatal 

 only when other debilitating causes are at work simulta- 

 neously. 



