rds are very
unfortunate and inappropriate. Many of these shelving or bracket fungi
are perennial and live from year to year. They may therefore be found
during the winter as well as in the summer. The writer has found
specimens over eighty years old. The shelves or brackets are the fruit
bodies, and consist of the pileus with the fruiting surface below. The
fruiting surface is either in the form of gills like _Agaricus_, or it
is honey-combed, or spinous, or entirely smooth.

[Illustration: FIGURE 10.--Polyporus borealis. Strands of mycelium
extending radially in the wood of the same living hemlock spruce shown
in Fig. 9. (Natural size.)]

=Mycelium of the Wood Destroying Fungi.=--While the fruit bodies are on
the outside of the trunk, the mycelium, or vegetative part of the
fungus, is within the wood or bark. By stripping off the bark from
decaying logs where these fungi are growing, the mycelium is often found
in great abundance. By tearing open the rotting wood it can be traced
all through the decaying parts. In fact, the mycelium is largely if not
wholly responsible for the rapid disintegration of the wood. In living
trees the mycelium of certain bracket fungi enters through a wound and
grows into the heart wood. Now the heart wood is dead and cannot long
resist the entrance and destructive action of the mycelium. The mycelium
spreads through the heart of the tree, causing it to rot (Fig. 10). When
it has spread over a large feeding area it can then grow out through a
wound or old knothole and form the bracket fruit body, in case the
knothole or wound has not completely healed over so as to imprison the
fungus mycelium.

[Illustration: PLATE 2, FIGURE 11.--Mycelium of Agaricus melleus on
large door in passage coal mine, Wilkesbarre, Pa. (1/20 natural size.)]

=Fungi in Abandoned Coal Mines.=--Mushrooms and bracket fungi grow in
great profusion on the wood props or doors in abandoned coal mines,
cement mines, etc. There is here an abundance of moisture, and the
temperature conditions are more equable the year around. The conditions
of environment then are very favorable for the rapid growth of these
plants. They develop in midwinter as well as in summer.

=Mycelium of Coal Mine Fungi.=--The mycelium of the mushrooms and
bracket fungi grows in wonderful profusion in these abandoned coal
mines. So far down in the moist earth the air in the tunnels or passages
where the coal or rock has been removed is at all time