TREES AND TIMBEB 



421 



White rot {Polyporus squamosus (Huds.) Fr.). — In 

 Europe this rot affects several species of maples, the pear, 

 oak, elm, walnut, linden, willow, ash, birch, beech, and 

 horse-chestnut. In 

 America it has been 

 reported from Min- 

 nesota. The wood 

 becomes imusually 

 white and bears scat- 

 tered series of white 

 lines. 



The nearly circular 

 fruiting bodies are 

 stalked and often at- 

 tain a diameter of 15 

 cm. \Mien young, 

 they are soft, but 

 later become very 

 tough. The upper 

 surface is scaly and 

 rough. 



Sapwood rot 

 {Fomes fomcntarivs 

 (L.) Fr.). — This rot 

 abounds throughout the northern part of the United States, 

 as one of the most common diseases of deciduous trees, 

 chiefly affecting the beech, white, paper, and yellow birches. 



Decay begins in the outer sapwood and proceeds inward. 

 The wood is marked by irregular black Unes, the boundaries 

 between diseased and normal wood. Wben wholly rotten, 

 the wood is soft and spongy and light yellow in color. 



Fig. 181. — Fomes fomentanus showing hoof-shaped 

 sporophore. After Atkinson. 



