DISEASES OF ECONOMIC PLANTS 



trunk. The fungus has also been 

 trees many years after they had died. 



found growing on 

 Neighboring trees 



Fig. 185. — Log rotted by Polyporus Schweinitzii. 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 vitse, and pine, by weakening the 

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



