OAK DISEASES 



253 



and the larger roots. The decay extends from the surface of 

 the ground upward in the heartwood for a distance of one to a 

 few feet and in its final stages leaves a large hollow cavity. 



Symptoms. 



When badly rotted trees are cut, they fall after the thin shell 

 of heartwood is cut through and the trunk carries with it the 

 partially rotted hollow cylinder of wood from the stump. The 

 odor of the freshly cut rotted wood is very strong and resembles 

 anise oil. The first indication of the decay is seen in longi- 

 tudinal section as a yellowish or whitish area from four to eight 



Fig. 50. — Fruiting-body of Polyporus Berkeleyi. 



inches long. The summer-wood in this region is delignified 

 and the ipdividual fibers are separated by the dissolving of the 

 cementing layer between them. As the decay progresses the 

 dense whitish summer-wood is completely destroyed. This 

 leaves the medullary-rays and strands of porous spring-wood 

 intact. The interwoven rays and strings of wood are brownish 

 at first but soon are covered with whitish mycelium. The 

 strands slowly become more brittle and finally collapse, leaving 

 a hollow cavity. The decayed area becomes larger and is 

 bordered by a zone of whitish wood with the string and ray 

 rot stage projecting into the hollow cavity. 

 The sporophores arise from the exposed larger roots or may 



