In the genus Agaric us the spores at maturity are either purple-brown in mass or blackish with a purple tinge. The annulus is present on the stem, though disappearing soon in some species, and the stem is easily separated from the substance of the pileus. The gills are free from the stem, or only slightly adnexed. The genus is closely related to Stropharia and the species of the two genera are by some united under one genus (Psalliota, Hennings). Peck, 36th Report, N. Y. State Mus., p. 41-49, describes 7 species. Lloyd Mycol. Notes, No. 4, describes 8 species. C. O. Smith, Rhodora, I: 161-164, 1899, describes 8 species.

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.

*For analytical key to the genera see Chapter XXII (Chemistry And Toxicology Of Mushrooms).

Figure 17. Agaricus rodmani

Figure 17

Agaricus rodmani. Entirely white, showing double veil or ring.

(Natural size.) Copyright.

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).

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.

The pileus is rounded, and then convex, very firm, compact and thick, with white flesh. The gills are crowded, first white, then pink, and in age blackish brown. The stem is very short, solid, nearly cylindrical, not bulbous. The annulus is quite characteristic, being very thick, with a short limb, and double, so that it often appears as two distinct rings on the middle or lower part of the stem as shown in Fig. 17. This form of the annulus is probably due to the fact that the thick part of the margin of the pileus during the young stage rests between the lower and upper part of the annulus, i. e., the thick veil is attached both to the inner and outer surface of the margin of the cap, and when it is freed by the expansion of the pileus it remains as a double ring. It is eagerly sought and much relished by several persons at Ithaca familiar with its edible qualities. The plant closely resembles A. campestris var., edulis, Vittad. (See Plate 54, Bresadola, I Funghi Mangerecci e Velenosi, 1899) and is probably the same.

Figure 18. Agaricus arvensis, fairy ring

Figure 18

Agaricus arvensis, fairy ring.

Agaricus (Psalliota) arvensis Schaeff. Edible. - The field mushroom, or horse mushroom, Agaricus arvensis, grows in fields or pastures, sometimes under trees and in borders of woods. One form is often white, or yellowish white, and often shows the yellow color when dried. The plant sometimes occurs in the form of a fairy ring as shown in Fig. 18. It is 5-12 cm. high, the cap from 5-15 cm. broad and the stem 8-15 mm. in thickness.

Figure 19. Agaricus silvicola

Figure 19

Agaricus silvicola. White to cream color, or yellow stains.

(Natural size.) Copyright.

The pileus is smooth, quite thick and firm, convex to expanded. The gills are first white, then tinged with pink and finally blackish brown. The stem is stout, nearly cylindrical, hollow, bulbous. The veil is double like that of Agaricus placomyces, the upper or inner layer remaining as a membrane, while the lower or outer layer is split radially and remains in large patches on the lower surface of the upper membrane.