SOME PARASITIC POLYPORACEAE. 
BY CLARENCE D. LEARN. 
Up to within the past eight or ten years, very little attention had been paid 
in America to the study of those forms of fungi causing forest diseases. The 
reasons are obvious. Previously, the occurrence of a few diseased trees was 
practically unnoticed, due to the vast area of our forests. But, with the ad- 
vance of the lumberman in the last decade, the situation has changed, and a 
demand has arisen among all classes of people for a more economical and 
rational treatment of the existing forest lands. The diseased trees of the 
primeval forest were ignored, as they were so few in comparison with the 
sound ones. While now the marked appreciation in the value of timber, cause 
the timber destroying agencies to become of immediate interest. These silent 
enemies of the forest are working here and there, not 'attracting the attention 
of the casual observer as do the careless habits of the lumberman and the 
forest fires. 
The polypores were formerly supposed not to be of a parasitic nature, and 
the papers published upon them dealt only with the fruiting portion. While 
now their parasitic nature is established. The effect brought about through 
the growth of the fungus, is the important economic question which is con- 
sidered in the present paper. 
The field for work on forest diseases is a large one, and its possibilities are 
just becoming apparent. Compared with other fields of activity, there are but 
a few workers, among the more prominent of whom we might name Drs. von 
Schrenk, Spaulding, Metcalf, Hedgecock, and Professor Atkinson. The govern- 
ment is just beginning to take cognizance of these fungi as producing diseases 
of forest, nut, and shade trees as is shown by Orton and Ames in Plant Diseases 
in 1907, where mention of them is made forty-eight times. 
In the present paper, I shall present a study of some of the higher fungi of 
the family Polyporaceae, and describe the characteristic changes which their 
mycelia induce in the wood of the trees in which they grow. These fungi were 
observed in the field causing the decay ascribed to them. 
The relation of the fungus to its host is a definite one. The question of the 
spore gaining its entrance is somewhat problematic. That any here studied 
gained entrance unaided, I believe is not safe to assert. Few of the fungi can 
gain an entrance unaided through the living layer of cambium tissue, which 
envelopes the entire tree, and while uninjured, serves as an effectual barrier 
against many of these enemies. For their entrance, fungi are usually de- 
pendent upon some agencies, usually gaining entrance through mechanical 
injuries to the host. There must be some condition conducive to infection, 
either a broken branch, a wound, or lack of vitality. When a tree once be- 
comes diseased, the mycelial threads spread rapidly, filling the heart wood with 
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