POPLAR DISEASES 



307 



pecially apple, are often attacked when orchards are near 

 forested areas. The maples, especially striped and silver, 

 are commonly attacked when mixed in the forest with beech 

 and aspen. Trees of all ages become infected and it is not 

 imcommon to find ninety per cent or more of second growth 

 trees less than five inches in diameter severely decayed. The 

 form of the fruiting-bodies and the characters of the decay are 

 similar for all the kinds of trees affected. 



Symptoms. 



Cross-sections of limbs or trunks affected by the common 

 white wood-rot show that the decay starts in the center of the 

 heartwood and gradually extends outward toward the sap- 

 wood. The outline 

 of the decayed area 

 is never regular and 

 certain annual rings 

 are invaded on one 

 side before they are 

 on the other. The 

 decayed wood is 

 soft and whitish, 

 with but few cracks 

 orfissures. Numer- 

 ous narrow and 

 more or less con- 

 centrically arranged 

 black lines are com- 

 mon in the decayed 

 area. Bordering the white rotted area is_ a continuous black 

 line with a dark-colored zone between it and the normal 

 wood (Fig. 58). The black line marks the region of greatest 

 activity of the advancing mycelium in converting the normal 

 wood into the soft white product of decay. The sapwood and 



Fig. 59. — Fruiting-body of Fames igniarius. 



