s nearly saturated
with moisture. This abundance of moisture, with the favorable
temperature, permits the mycelium to grow on the surface of the wood
structures as readily as within the wood.

In the forest, while the air is damp at times, it soon dries out to such
a degree that the mycelium can not exist to any great extent on the
outer surface of the trunks and stumps, for it needs a great percentage
of moisture for growth. The moisture, however, is abundant within the
stumps or tree trunks, and the mycelium develops abundantly there.

So one can understand how it is that deep down in these abandoned mines
the mycelium grows profusely on the surface of doors and wood props.
Figure 11 is from a flashlight photograph, taken by the writer, of a
beautiful growth on the surface of one of the doors in an abandoned coal
mine at Wilkesbarre, Pa., during September, 1896. The specimen covered
an area eight by ten feet on the surface of the door. The illustration
shows very well the habit of growth of the mycelium. At the right is the
advancing zone of growth, marked by several fan-shaped areas. At the
extreme edge of growth the mycelium presents a delicate fringe of the
growing ends where the threads are interlaced uniformly over the entire
area. But a little distance back from the edge, where the mycelium is
older, the threads are growing in a different way. They are now uniting
into definite strands. Still further back and covering the larger part
of the sheet of mycelium lying on the surface of the door, are numerous
long, delicate tassels hanging downward. These were formed by the
attempt on the part of the mycelium at numerous places to develop
strands at right angles to the surface of the door. There being nothing
to support them in their attempted aerial flight, they dangle downward
in exquisite fashion. The mycelium in this condition is very soft and
perishable. It disappears almost at touch.

On the posts or wood props used to support the rock roof above, the
mycelium grows in great profusion also, often covering them with a thick
white mantle, or draping them with a fabric of elegant texture. From the
upper ends of the props it spreads out over the rock roof above for
several feet in circumference, and beautiful white pendulous tassels
remind one of stalactites.

[Illustration: FIGURE 12.--Agaricus campestris. Spore print. (Natural
size.)]

=Direction in Growth of Mushrooms.=--The direction of growth which these