West: Undescribed Timber Decay of Hemlock 265 



ting paper. As the rot progresses, numerous checks or horizontal 

 cracks appear. These do not appear to be due to shrinkage but 

 rather to have been dissolved out by the action of the hyphae. 

 They extend individually only through a single layer of spring- 

 wood, but in the later stages of the decay, short vertical cracks 

 connect the horizontal and a complete network is formed which 

 becomes completely filled with white mycelium. The wood at 

 this stage splits very easily along the annual rings into con- 

 centric layers. On the inner side of these layers, the network of 

 cracks filled with the white mycelium, shows up very conspicu- 

 ously. At the same time or a little before, numerous black dots 

 make their appearance at irregular intervals throughout the de- 

 cayed wood. They increase in number and sometimes form lines 

 as the wood goes into the later stages of decay. They are more 

 or less distinct in outline and are harder than the surrounding 

 wood. They vary slightly in color but are usually so dark a 

 brown that they appear black to the unaided eye. They are 

 usually not more than a few millimeters in any dimension. 



The fungus is primarily a cellulose destroyer but soon attacks 

 lignified structures also. The mycelium attacks first the medul- 

 lary rays and partially destroys them. All free cellulose is ab- 

 sorbed at this stage since various tests for it gave negative results 

 in the rays and traceids alike. The fungus now fills the ray cavi- 

 ties with a mass of tangled hyphae, frequently containing some 

 of the thick elements found in the context of the pileus. At 

 this same time it attacks the tracheids, starting at the bordered 

 pits. These are eaten out until only irregularly shaped holes 

 remain. The hyphae may now pass easily from one tracheid to 

 the next by simply dissolving a hole in the wall. The hyphae 

 branch freely throughout the wood and seldom pass from one ray 

 to the next without doing so. Clamp connections are very abund- 

 ant and seem to be the rule. Occasionally they occur at branches 

 and cause the mycelium to appear swollen at the joints, which is 

 not really the case. As a rule the hyphae are hyaline, slender, 

 4-8 /X in diameter, except in the rays mentioned above, and are 

 filled with many small oil globules. However where the black 

 spots appear, the hyphae are often thicker and shorter jointed 



