372 



Diseases of Economic Plants 



ests. In Europe, where it is greatly dreaded, it is customary 

 to prevent its spread by trenching. Groups of infected trees 

 and trees near them may be cut to advantage to protect other 

 trees. Other toadstool fungi that cause root-rot are Cli- 



FiG. 195. — Log rotted by Polyporus schweinitzii. After von Schrenk. 



tocybe, Tricholoma, and Septobasidium. Root-rots are also 

 due to other fungi, chiefly the following: 



Ozonium Root-rot (Ozonium omnivorum Sh.). — Elm, 

 basswood, oak, cottonwood, mesquite, china tree, mulberry, 

 apple, and pear are affected by this rot, which has been de- 

 scribed and discussed on page 23. 



