The Biology of Polyporus Pargamenus Fries 165 
plants, as the one studied here, seem to have acquired the 
ability to avail themselves of the parasitic habit, while dur- 
ing the greater part of their lives they are true saprophytes. 
In other words, at times in their development they may 
become parasitic, though nominally they are saprophy tic. 
Like many other fungi, Polyporus pargamenus possesses 
great adaptability, as shown by the fact that it attacks living 
tress as well as dead trees, stumps, and logs, thus showing 
that it may be either saprophytic or parasitic. Although it 
usually is found on dead wood, it may occur frequently on 
living trees where these have been severely wounded. This 
fungus is to be classed with the hemisaprophytes (the facul- 
tative parasites of DeBary). It is a plant that is wont to 
pass through its whole dev elopment as a saprophyte, its nat- 
ural habitat being moist dead wood ; under certain conditions, 
however, it may become a wound parasite. 
The effect of such a parasite on the host may remain 
unnoticed for some time, since the growth of the mycelium 
is very slow at first and only a few ‘wood cells are attacked. 
Upon becoming securely established within the tissues of 
the host, the mycelium spreads rapidly, permeating a larger 
volume of wood. After the mycelium penetrates the tissues 
of the host to a sufficient extent to be-enabled to extract from 
them adequate nutrient materials for its sustenance, thereby 
causing what we call decay, it may produce fruiting bodies. 
The appearance of the fruit bodies often is the first notice- 
able indication of the presence of a fungous disease (Plate 
XXX.) The first appearance of the fruit-bodies on the 
bole of the infected tree, therefore, gives us an indication 
of the approximate development of the mycelium within the 
sapwood. As the vegetative part of the fungus increases in 
consequence of its age, so does the number of fruit-bodies 
increase. The dead portion of the sapwood is disintegrated 
slowly and, from contact with this, the adjoining living cells 
are reduced in vitality and ultimately die. When this stage 
is reached the effect on the host may be noticed in the dead 
branches at the top of the tree and the pale color of the 
remaining foliage. The fruit-bodies, like most annual ones, 
