irregular and the margin wavy,
especially when old. It is quite firm, but the margin splits quite
readily on being handled. The color varies greatly, white, yellowish,
gray, or brownish and lilac tints. The flesh is white. The =stems= are
usually attached to the pileus, at or near one edge. The =gills= are
white, broad, not at all crowded, and extend down on the stem as in the
oyster agaric. They are white or whitish, and as in the other related
species are sometimes cracked, due probably to the tension brought to
bear because of the expanding pileus. The =spores= are tinged with lilac
when seen in mass, as when caught on paper. The color seems to be
intensified after the spores have lain on the paper for a day or two.

It is very difficult to distinguish this species from the oyster agaric.
The color of the spores seems to be the only distinguishing character,
and this may not be constant. Peck suggests that it may only be a
variety of the oyster agaric. I have found the plant growing from a dead
spot on the base of a living oak tree. There was for several years a
drive near this tree, and the wheels of vehicles cut into the roots of
the tree on this side, and probably so injured it as to kill a portion
and give this fungus and another one (_Polystictus pergamenus_) a start,
and later they have slowly encroached on the side of the tree.

Figure 108 represents the plant (No. 3307, C. U. herbarium) from a dead
maple trunk in a woods near Ithaca, collected during the autumn of 1899.
This plant compares favorably with the oyster agaric as an edible one.
Neither of these plants preserve as well as the elm pleurotus.

=Pleurotus dryinus= Pers. =Edible.=--_Pleurotus dryinus_ represents a
section of the genus in which the species are provided with a veil when
young, but which disappears as the pileus expands. This species has been
long known in Europe on trunks of oak, ash, willow, etc., and occurs
there from September to October. It was collected near Ithaca, N. Y., in
a beech woods along Six-mile creek, on October 24th, 1898, growing from
a decayed knothole in the trunk of a living hickory tree, and again in a
few days from a decayed stump. The pileus varies from 5--10 cm. broad,
and the lateral or eccentric stem is 2--12 cm. long by 1--2 cm. in
thickness, the length of the stem depending on the depth of the
insertion of the stem in a hollow portion of the trunk. The plant is
white or whitish, and the substance is quite fir