OAK DISEASES 251 



larly destructive and common in the Southwest and along the 

 Pacific Coast. In poplar it is found rarely and then often fol- 

 lowing the common white wood-rot caused by F. igniarms. The 

 white pocketed rot of the heartwood of oaks is confined largely 

 to the upper portions of the larger and older trees. 



Symptoms. 



The first evidence of this rot in oaks is a discolored water- 

 soaked area in the heartwood. Later delignification results in 

 the medullary-rays turning white. In longitudinal section 

 this produces a mottled appearance of white irregular lines 

 running lengthwise and broader white areas joining these at 

 intervals. The wood between these white areas is slightly dis- 

 colored. In more advanced stages, the white areas involve 

 adjacent tissues and become more extensive and less definitely 

 linear. The small amount of discolored wood between the 

 white areas remains firm. Irregularly distributed in the de- 

 cayed wood are brown areas varying from an eighth to a half 

 inch across. The wood surrounding the white pocketed surface 

 is discolored and water-soaked. In some species the symptoms 

 vary slightly from those described above. In chestnut oak 

 the spring-wood of the annual rings is yellowish white and the 

 tissue between these concentric zones is light brown. In 

 poplar the rot as seen in cross-section produces alternate zones 

 of whitish and yellow tissue. The same brown areas are present 

 as in the oak. 



The sporophores formed at branch wounds on the oaks are 

 flat and shelf-like or hoof-shaped, but when formed directly 

 from the bark they are almost globose. A peculiar diagnostic 

 character of these sporophores consists in a hard, granular 

 sandstone-like core with radiating white mycelial strands run- 

 ning through it. This core extends back into the rotted wood 

 of the tree for a short distance. The upper surface is rusty 

 yellow or brown and at first is hairy but later becomes smooth. 



