CHAPTER X. 



" CANKER " : THE LARCH DISEASE. 



THERE is a large and important class of diseases 

 of standing timber which start from the cortex and 

 cambium so obviously that foresters and horticulturists, 

 struck with the external symptoms, almost invariably 

 term them " diseases of the bark " ; and since most of 

 them lead to the production of malformations and 

 excrescences, often with outflowing of resinous and 

 other fluids, a sort of rough superficial analogy to 

 certain animal diseases has been supposed, and such 

 terms as " canker," " cancer," and so forth, have been 

 applied to them. 



Confining our attention to the most common and 

 typical cases, the following general statements may be 

 made about these diseases. They usually result from 

 imperfect healing of small wounds, the exposed cortex 

 and cambium being attacked by some parasitic or 



Q2 



