=Agaricus (Psalliota) campestris= Linn. =Edible.=--This plant has been quite fully described in the treatment of the parts of the mushroom, and a recapitulation will be sufficient here. It grows in lawns, pastures, by roadsides, and even in gardens and cultivated fields. A few specimens begin to appear in July, it is more plentiful in August, and abundantly so in September and October. It is 5--8 cm. high (2--3 inches), the cap is 5--12 cm. broad, and the stem 8--12 mm. in thickness. The =pileus= is first rounded, then convex and more or less expanded. The surface at first is nearly smooth, presenting a soft, silky appearance from numerous loose fibrils. The surface is sometimes more or less torn into triangular scales, especially as the plants become old. The color is usually white, but varies more or less to light brown, especially in the scaly forms, where the scales may be quite prominent and dark brown in color. Sometimes the color is brownish before the scales appear. The flesh is white. The =gills= in the young button stage are white. They soon become pink in color and after the cap is expanded they quickly become purple brown, dark brown, and nearly black from the large number of spores on their surfaces. The gills are free from the stem and rounded behind (near the stem). The =stem= is white, nearly cylindrical, or it tapers a little toward the lower end. The flesh is solid, though the central core is less firm. The =veil= is thin, white, silky, and very frail. It is stretched as the cap expands and finally torn so that it clings either as an annulus around the stem, or fragments cling around the margin of the cap. Since the =annulus= is so frail it shrivels as the plant ages and becomes quite inconspicuous or disappears entirely (see Figs. 1--7). [Illustration: FIGURE 17.--Agaricus rodmani. Entirely white, showing double veil or ring. (Natural size.) Copyright.] Variations in the surface characters of the cap and stem have led some to recognize several varieties. This is known as the common mushroom and is more widely known and collected for food than any other. It is also cultivated in mushroom houses, cellars, caves, abandoned mines, etc. =Agaricus (Psalliota) rodmani= Pk. =Edible.=--Rodman's mushroom, _Agaricus rodmani_, grows in grassy places along streets of cities, either between the curbing and the walk, or between the curbing and the pavement. It is entirely white or whitish and sometimes tinged with yellowish at the center of the pileus. The plants are 4--8 cm. high, the cap 5--8 cm. broad and the stem 1--2 cm. in thickness. [Illustration: FIGURE 18.--Agaricus arvensis, fairy ring.]