the stem is usually attached at
the center, and the majority of the species grow on the ground, while
the species of _Pleurotus_ are especially characterized by growing on
wood. Some species, at least, appear to grow from the ground, as in
Pleurotus petaloides, which is sometimes found growing on buried roots
or portions of decayed stumps which no longer show above ground. On the
other hand species of _Clitocybe_, as in C. candida (Fig. 91), often
have an eccentric stem. This presents to us one of the many difficulties
which students, especially beginners, of this group of fungi meet, and
also suggests how unsatisfactory any arrangement of genera as yet
proposed is.

=Pleurotus ulmarius= Bull. =Edible.=--The elm pleurotus is so called
because it is often found growing on dead elm branches or trunks, or
from wounds in living trees, but it is not confined to the elm. It is a
large species, easily distinguished from the oyster agaric and the other
related species by its long stem attached usually near the center of the
cap, and by the gills being rounded or notched at their inner extremity.
The cap is 5--12 cm. broad, the stem 5--10 cm. long, and 1--2 cm. in
thickness.

[Illustration: FIGURE 106.--Pleurotus ulmarius. Under view and section
(natural size). Copyright.]

The =pileus= is convex, the margin incurved, then nearly expanded,
smooth, firm, white or whitish, or with shades of yellow or brown on the
center, and the flesh is white. The =gills= are broad, rather distant,
sinuate, white or nearly so. The =spores= are globose, 5--8 mu in
diameter. The =stem= is firm, eccentric, usually curved because of its
lateral attachment on the side of the tree, and the horizontal position
of the pileus.

The elm pleurotus has been long known as an edible fungus, and is
regarded as an excellent one for food on account of its flavor and
because of its large size. It occurs abundantly during the late autumn,
and at this season of the year is usually well protected from the
attacks of insects. It occurs in the woods, or fields, more frequently
on dead trees. On shade trees which have been severely pruned, and are
nearly or quite dead, it sometimes appears at the wounds, where limbs
have been removed, in great abundance. In the plants shown in Fig. 105
the stems are strongly curved because the weight of the cap bore the
plant downward. Sometimes when the plant is growing directly on the
upper side of a branch or log, the stem may