As they grow older, especially after they are picked, the gills turn in a few hours to a light brown and finally to a dark chestnut-brown, almost black, color. The usual diameter of fully-expanded specimens of the common mushroom is one and a half to three inches, though smaller and larger specimens are some times found. When one day old, a mush room is usually still edible, but insect larvae soon attack it, traveling up through the stem into the cap, and de composition rapidly follows.
About Washington the common mush room occurs oftenest on lawns and in pastures and especially in neglected fields where weeds have been succeeded by a scant covering of grass. F. V. Coville (Circ. No. 13, Division of Botany, U. S. Dept. of Agriculture, '93).
While the horse-mushroom (A garieus arrensis, Schaeffer—Figs. 2 and 3) agrees in most details with the common mush room, the surface of the cap is darker colored than in cam pcstris, though speci mens of a considerably lighter shade of brown are often found; it is larger, and the ring is wider and thicker than in the other. Usually the ring is distinctly marked on its upper surface by a series of lines where the edges of the gills before expansion have pressed against it. The horse-mushroom is not always dis tinguished from the common mushroom by the market people, and, indeed, in its technical characteristics it is closely re lated to that species. Its characteristic place of growth about Washington is not in fields, but in gardens, especially very rich or heavily fertilized ones, where it often occurs in cold frames or around hot beds. F. V. Coville (Circ. No. 13, Division of Botany, U. S. Dept. of Agri culture, '98).
In the fairy-ring mushroom (Fig. 5— Marasmius arcades, Bolt, Fr.) the stem has no ring. The gills are comparatively few and far apart; and the cap, as it be comes widely expanded, has a peculiar knob-like projection in the centre. The cap and stem have a pinkish-buff color, and the gills a lighter shade of the same, varying in its younger stages toward a cream color. The spores are white, and in ascertaining their color the cap should be laid on some dark-colored, preferably black, paper. The fairy-ring mushroom is one of the commonest species on the lawns in the city of Washington. In general, they can be found in any old and well kept lawn. The ring (Fig. 4) is due to the
uniform annual growth of the mycelium. This, starting at a central point, grows each year a few inches outward, the older portion beginning to die at the centre. Thus a small circular band is formed and each year this increases in size, growing regularly on the outside and dying as regularly on the inside.
The fairy rings, except when young, seldom form complete circles, usually ap pearing as broken rings or crescents. Several crops of mushrooms are produced on a single ring during a season. The most abundant crop coming after the autumn rains. F. V. Coville (Circ. No. 13, Division of Botany, U. S. Dept. of Agriculture, '9S).
Not only are the spores of the shaggy mushroom black, but the whole plant, beginning at the outer edge of the cap, dissolves when the mushroom is about a day old, into an inky-black fluid (Fig. 6). Some of this inky fluid has dropped from the large specimen upon the small one at the left and has run down its stem. At the right is a specimen showing the characteristic appearance of the cap which, except in its latest stages. has somewhat the form of a closed umbrella. In their early stages the cap, gills, and stem are white, excepting frequently the apex of the cap, which is often dark colored, as in the figure. The surface of the cap is covered with delicate lacerated scales. The ring is only very loosely at tached, either to the stem or to the mar gin of the cap, and sometimes is wholly free from both, early dropping down to the base of the stern. In the white part of the cap the juice is as colorless as water; toward the margin it is wine colored. In this stage the mushroom is still in condition to be eaten, but when the juice turns black the mushroom is too old for the table. This mushroom has as its favorite place of growth, not fields and pastures, but shaded situations, where the ground is rich or well supplied with thoroughly decomposed wood or other vegetable matter.
It grows in greatest abundance in the low grounds near the Potomac, shaded by willows or rank weeds. The season of greatest abundance is the late autumn, in November and early December. F. V. Coville (Circ. No. 13, Division of Botany, U. S. Dept. of Agriculture, '98).