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. [Illustration: FIGURE 19.--Agaricus silvicola. White to cream color, or yellow stains. (Natural size.) Copyright.] =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. 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. [Illustration: FIGURE 20.--Agaricus silvicola, showing radiately torn lower part of veil. (Natural size.) Copyright.] =Agaricus (Psalliota) silvicola= Vittad. =Edible.=--The _Agaricus silvicola_ grows in woods, groves, etc., on the ground, and has been found also in a newly made garden in the vicinity of trees near the woods. It is an attractive plant because of its graceful habit and the delicate shades of yellow and white. It ranges from 10--20 cm. high, the cap is 5--12 cm. broad and the stem 6--10 mm. in thickness.