POLYPORACEOUS WOOD-ROTS OF TREES 
The wood-rots of trees, as a class of diseases, catise more economic loss 
than any other type of enphytotic disease of trees. The difficulty in con- 
trolling wood-rot diseases is due largely to their insidious nature and to the 
relatively small amount of work which has been done on them. The 
control of wood-rots in the forest is one of the important measures In 
forest-management, which must soon be recognized. Since the fruit- 
bodies of the fungi causing wood-rots are the chief signs by which these 
diseases may be recognized, it is important that the student gain a working- 
knowledge of their identification. 
SYMPTOMS 
Sections from different deciduous and coniferous trees, showing the 
character of a few common wood-rots, are provided. OBSERVE:— 
1. That the decayed wood is, in some cases, darker in color than 
in the normal, usually reddish or brownish. Such wood-rots are called 
“sed-rots.” The color is caused by residual substances left by the causal 
fungus. DRAW. 
2. In other cases the rotted wood is lighter in color than the 
normal wood and often is almost white. Such wood-rots are called ‘‘white- 
rots.” The change in color is due to the delignification of the wood-ele- 
ments, leaving the whitish cellulose cell-walls. No colored residue is 
left as in the red-rots. DRAW. 
3. That certain wood-rots at first appear in the heart-wood 
and work out toward the sap-wood, while others work from the start 
chiefly in the sap-wood. The former are known as “‘heart-rots” and the 
latter as ‘‘sap-rots.”” DRAW. 
4. That, in some wood-rots, the tissue is entirely decayed leaving 
holes or pockets. Usually these holes are surrounded by a white border 
that represents the cellulose fibers which were not dissolved. DRAW. 
5. That, in other cases, the decay results in a uniform change to 
a weak cellulose structure but in no place are the tissues entirely destroyed. 
DRAW. 
6. The black lines bordering the decayed portion of the wood in 
many wood-rots. This line is usually due to both the color of the feeding- 
hyphae and to the first products of the decay-process in solution in the sap. 
DRAW. 
ETIOLOGY 
The majority of wood-rots are caused by basidiomycetous fungi be- 
longing to the two large families, Agaricaceae (toad-stools) and Poly- 
poraceae (polypores or bracket-fungi). The polypores are by far the more 
important of the two groups. 
The main distinction between the Agaricaceae and Polyporaceae is in 
the morphology of the under side of the fruit-body. The hymenium, each 
basidium of which bears four sporidia on sterigmata, is spread over the 
plate-like or tube-like surfaces which hang vertically from the cap or pileus. 
Examine the prepared sections of the hymenium of a toad-stool or 
polypore with the microscope. OBSERVE :— 
_ 7. The irregular tangled mycelium making up the trama or 
supporting-structure for the hymenium. 
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