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 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 µ 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.]