256 MANUAL OF TREE DISEASES 



discolored region and develop into white pockets. They are 

 located partiaUy in the porous spring-wood of one ring and in 

 the summer-wood of the adjoining ring. Later the pockets 

 become hollow and have a white lining. They become larger 

 in time until finally limited by reaching a large medullary- 

 ray on each side. Only a narrow layer of brownish wood 

 separates the adjoining pockets. In longitudinal sections, the 

 pockets are seen to be from three to five times as long as wide. 

 The discolored area extends from one to six feet beyond the 

 region showing the pockets. In the first stages of the decay, 

 this rot closely resembles the white piped butt-rot caused by 

 Polypory^ croceus (see page 258). The latter rot usually ex- 

 tends its activities more rapidly upward than radially, causing 

 the decay of a few annual rings, while the honeycomb-rot in 

 white oak, at least, spreads uniformly in both directions. 

 Freshly cut wood affected by this rot is said to have the odor 

 of old honeycomb. 



The sporophores are rarely available to identify this rot in 

 living trees, except when a large area of the affected heartwood 

 is exposed. Sporophores develop on the felled timber in a 

 year or two and continue to form for several years. They are 

 from a quarter of an inch to two inches wide, rather thick 

 shelving bodies occurring one over the other in long rows. The 

 upper surface is at first downy and light yellowish brown, later 

 becoming smooth and gray. Concentric furrows mark the 

 upper surface into zones which vary in color. The under 

 surface is light yellowish brown and smooth. 



Caiise. 



The honeycomb heartwood-rot of oaks is caused by the 

 fungus, Stereum subpUeatum. The fruiting-bodies described 

 above are annual structm-es which become dry and persist 

 through the ^\Tnter and may revive the following season. The 

 spores are borne over the entire smooth under surface of the 



