16 College of Forestry 
value of the timber produced, either by diminishing the 
value of the wood cut or by retarding or preventing the 
growth of the trees themselves. 
Polyporus pargamenus, while of rare occurrence on 
coniferous woods, grows on all or nearly all of the dico- 
tyledonous woods occurring within its range, especially on 
the sapwood, and exhibits no perceptible preference for any 
particular species. On account of its wide geographic dis- 
tribution and its ability to grow on and destroy so many 
different kinds of wood it should be regarded, in the United 
States at least, as second probably only to its near relative, 
Polyporus versicolor (L.) Fr., in being the most common of 
the wood-destroying fungi which attack the dead wood of 
dicotyledonous trees. As a usual rule Polyporus pargamenus 
is confined to dead trees and fallen woody parts, although 
frequently it may become a wound parasite and thus attack 
living trees whenever they become injured. ‘The decay is 
at first restricted to the sapwood, but, under favorable con- 
ditions, after the destruction of the sapwood the fungus may 
advance and gradually decay the heartwood also. Thus the 
whole tree may be rendered valueless for lumber and of but 
little value for fuel. To the living forest trees, therefore, 
this class of fungi is a constant menace, and to the dead trees 
and fallen trunks, almost a certain evil. 
These saprophytes are of great importance in two ways. 
From the standpoint of man’s narrower economy they are 
directly injurious by virtue of the enormous losses sustained 
as a result of the decay of wood and timbers. From the 
standpoint of the -broader economy of nature they are the 
scavengers which retard the accumulation of plant débris. 
As such their ability vastly outweighs those effects detri- 
mental to man’s interest. 
It was not until 1833 that we had the first attempt, by 
Theodor Hartig, at a scientific investigation of the decay 
of wood. Of course the earlier explanations of the causes 
of disease were bound to be defective in accordance with the 
condition of botanical science at that time, but with the 
advent of time the basic principles became established 
