100 
over which the dissemination of primary inoculum takes place may, 
however, be long, as the sporophores of polypores often cease spore- 
production under adverse weather-conditions. With more favorable 
conditions it is resumed. 
Pathological Histology. The decay-process caused by this fungus in 
spruce is of two kinds. In the cross- and longisections of spruce wood 
where pockets are not formed, NOTE :— 
21. That the medullary ray-cells are destroyed and from these 
the mycelium spreads to the adjoining tracheids. DRAw. 
22. That the elements of the spring wood are destroyed before 
the thicker-walled summer elements. 
23. That the first noticeable change in the cell-walls is the separa- 
tion of the middle wall-layer from the outer layer. It has not been deter- 
mined that this is due to the shrinking of the middle layer as a result of 
the disintegration of the outer layer. DRaw. 
24. That when a hypha makes a hole through a cell-wall the 
hole is at first cylindrical but changes by enlarging in the middle. Draw. 
25. That the outer wall-layer of each cell separates from the 
outer wall-layer of the neighboring cell. DRaw. 
26. That, following this stage, the middle wall-layer is changed 
into cellulose. Then there are left for a time only the outer and inner 
lignified layers which later also change to cellulose. DRAW. 
27. That the middle layer disappears first, then the outermost 
layer is dissolved. DRAW. ; 
28. That the only portion of the wall resisting decay is the inner- 
most layer of the cell-wall. pRaw. 
In cross- and longisections of spruce wood where pockets are formed, 
NOTE :— 
29. The general appearance of the pockets under low-power; 
their location, abundance of mycelium, and the black lines surrounding 
the pockets. DRAW. 
30. The black line under the high-power. Of what is it com- 
posed? DRAW. 
31. The fine mycelium around the margin of the pocket. 
DRAW. 
32. That the progress of the decay around the margin of the 
pocket proceeds as follows:—The entire wall is changed into cellulose; 
the elements become separated by the dissolving of the middle-lamella; 
the outermost wall-layer then dissolves and the wall becomes thinner 
and thinner until only the innermost layer is left. DRAW showing the 
progressive stages. 
REPORT 
1. From the studies made of this decay-process, write a concise 
account of the steps involved. (See U.S. Agr. Dept., Veg. Phys. and Path. 
Div. Bul. 25:31-40, pl. VI-X.) 
