FUNGI 275 



flows from branch stubs serve as indications, while soundings 

 on the trunk often furnish information. An increment borer 

 is useful for taking borings to determine the internal condi- 

 tion of the tree. 



A humid atmosphere, at least in the zone in which the 

 fungi are developing, favors their growth because both the 

 mycehum and the sporophores dry out very easily and require 

 large amounts of water. 



The regions where fungi are found in greatest profusion 

 have humid, relatively warm cKmates, which produce a dense 

 forest; and within such regions the stands growing on damp 

 soils are likely to show the greatest injury. The effect of 

 climatic factors such as temperature, sunlight, and moisture 

 apparently is not the same for all "groups of fungi ^ ^^^ ^ and 

 still furnishes a field for investigation. With advancing age 

 the amount of injury and the production of sporophores 

 increases.* 



Extent and Character of the Injury. — Both insects and fire 

 are more destructive in their effects upon the forest than 

 are fungi. Yet the latter have the capacity for inflicting 

 injury on a large scale. Witness the chestnut blight, Endo- 

 thia parasitica, which has exterminated commercially the 

 chestnut {Castanea dentatd) over thousands of square miles 

 along the Atlantic seaboard in a period of less than 20 years. 

 The rapidity of this attack and the completeness of the 

 destruction over a large region are not characteristic of the 

 work of most species of fungi. 



On the average they work more slowly than fire and in- 

 sects, are disseminated unnoticed, may exist within their tree 

 hosts for many years before revealing their presence and often 

 consume several decades in accomplishing the death and 

 destruction of a single tree. 



The extent of the damage caused by fungi is more difficult 



