426 DISEASES OF i;CONOMIC PLANTS 



trunk. The fungus has also been found growing on 

 trees many years after they had died. Neighboring trees 



Fig. 185. — Log rotted by Polyporus Schweiaitzii. After von Schrenk. 



generally become infected from a diseased tree, through the 

 small fibrous roots. 



Root rot {Polyporus Schweinitzii Fr.). — A destructive 

 root rot of spruce, fir, arbor vitae, and pine, by weakening the 

 root or trunk, leads to the overthrow of the tree by wind. 



