be central.

=Pleurotus ostreatus= Jacq. =Edible.=--This plant is known as the oyster
agaric, because the form of the plant sometimes suggests the outline of
an oyster shell, as is seen in Fig. 107. It grows on dead trunks and
branches, usually in crowded clusters, the caps often overlapping or
imbricated. It is large, measuring 8--20 cm. or more broad.

The =pileus= is elongated and attached at one side by being sessile, or
it is narrowed into a very short stem. It is broadest at the outer
extremity, where it becomes quite thin toward the margin. It is more or
less curved in outline as seen from the side, being depressed usually on
the upper side near the point of attachment, and toward the margin
convex and the margin incurved. The color is white, light gray, buff or
dark gray, often becoming yellowish on drying. The =gills= are white,
broad, not much crowded, and run down on the stem in long elevated lines
resembling veins, which anastomose often in a reticulate fashion. The
=spores= are white, oblong, 7--10 mu long. The =stem= when present is
very short, and often hairy at the base.

The oyster agaric has long been known as an edible mushroom, but it is
not ranked among the best, because, like most _Pleuroti_, it is rather
tough, especially in age. It is well to select young plants. Figure 107
is from plants (No. 2097, C. U. herbarium) collected at Ithaca, N. Y.

[Illustration: PLATE 34, FIGURE 107.--Pleurotus ostreatus. Under view
showing decurrent and anastomosing gills on the stem. Cap white, light
gray, buff, or dark gray in color. Spores white (natural size, often
larger). Copyright.]

=Pleurotus sapidus= Kalchb. =Edible.=--This plant usually grows in large
clusters from dead trunks or branches or from dead portions of living
trees. It grows on a number of different kinds of trees. The stems are
often joined at the base, but sometimes the plants are scattered over
a portion of the branch or trunk. The cap is from 5--10 cm. broad.
The plants occur from June to November.

[Illustration: PLATE 35, FIGURE 108.--Pleurotus sapidus. Color of cap
white, yellowish, gray, or brownish, with lilac tints sometimes. Spores
lilac tinted in mass (1/2 natural size). Copyright.]

The =pileus= is convex, the margin incurved when young, and more or less
depressed in age, smooth, broadened toward the margin and tapering into
the short stem, which is very short in some cases and elongated in
others. Often the caps are quite