24 
IOWA ACADEMY OF SCIENCE 
holes or changing it to a brittle substance having none of the properties of 
wood. These changes weaken the trunk, and now it is only a question of 
time until the tree is broken by the wind. 
That some fungi possess great adaptability is shown by Elfvingia megaloma, 
which attacks both living and dead trees, as well as stumps and logs, showing 
it to be both parasitic and saprophytic. Pyropolyporus conchatus also has this 
dual nature. The greater majority of parasitic diseases, however, is induced by 
a wound. As stated before, in most instances there must be some means for 
the spore to gain access other than directly through the cambium layer. Hence 
if it be true that injury is necessary for infection, we might decrease the pos^ 
sibility of attack by care in handling trees to be transplanted, in pruning, and 
also in protection. The true parasite is not to be found among the specimens 
under consideration in this paper. Very few wood rotting fungi are capable 
of entering an uninjured tree. Nearly all gain lodgement in wounds, grow in 
from these, and rot the wood. 
The effect of parasite on the host may remain unnoticed for some time, as 
the growth is very slow. The first noticeable indication of . the presence of a 
fungus disease is the sporophore. As the age of the fungus increases the 
greater is the number of sporophores, of which I have seen as many as twenty- 
five on a single host. When this stage is reached, the effect may be noticed in 
the dead branches at the top, and pale color of foliage. When the host becomes 
thus infected it succumbs to the wind by either being broken off or up-rooted. 
A microscopic examination of some of these diseases shows that the wood 
tissues are penetrated by tiny mycelial threads. These threads are seen to 
attach themselves to the cell walls, and to pierce it in all directions. Thus 
these tiny threads form a network in the wood, and as they increase in number, 
they dissolve the walls of the wood cells converting them into food for their 
own consumption. In some cases it is the woody cell wall alone that is 
attacked; in other cases they consume the starch found in the cells; but 
in all cases of decay we find these mycelial threads are responsible for the 
mischief. These fine threads are the vegetative body of the fungus, the little 
shelf its fruiting body, on which it produces myriads of tiny spores. 
The economic side of the problem is also worthy of our consideration. We 
find that there are but a very few kind of trees, if any at all, that are not sub- 
ject to fungus diseases; and that both dead and living trees are attacked. A 
tree does not lie on the ground any time until it is nearly covered with fungus 
growth. If one is to realize any value from diseased trees they must be used 
before they reach the last stage, or before they fall. Some of these diseases 
affect the heart wood, rendering it useless for lumber, and . of little value as 
fuel. That this problem is of the greatest importance is evidenced by the 
attitude of the government in studying its character, and trying to determine 
some means of prevention. 
The species discussed in this paper are the most characteristic and common 
of this region, infesting our chief forest trees. They are Pyropolyporus ignior 
rius (L.) Murrill; Pyropolyporus Everhartii (Ellii & Gall.) Murrill; Pyropoly- 
porus fulvus (Scop.) Murrill; and Elfvingia megaloma (Lev.) Murrill. 
Pyropolyporus igniarius: The sporophores of this fungus are among the 
commonest and best known of the largest fungi. The hoof-like shelves of this 
fungus occur widely distributed throughout the United States on the apple, oak, 
alder, beech, birch, maple and other species of broad leaved trees. In Plant 
