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In the genus Agaricus 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. 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).

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.

Figure 18.—Agaricus arvensis, fairy ring.

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 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.

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.

The pileus becomes convex, and expanded or nearly flat, and often with an elevation or umbo in the center. It is thin, smooth, whitish and often tinged more or less deeply with yellow (sulfur or ochraceous) and is sometimes tinged with pink in the center. The flesh is whitish or tinged with pink. The gills when very young are whitish, then pink, and finally dark brown or blackish brown, much crowded, and distant from the stem. The stem is long, nearly cylindrical, whitish, abruptly enlarged below into a bulb. It is often yellowish below, and especially in drying becomes stained with yellow. The ring is thin, membranaceous, delicate, sometimes with broad, soft, floccose patches on the under side. The ring usually appears single, but sometimes the veil is seen to be double, and the outer or lower portion tends to split radially as in A. arvensis or A. placomyces. This is well shown in large specimens, and especially as the veil is stretched over the gills as shown in Fig. 20.

From the form of the plant as well as the peculiarities of the veil in the larger specimens, it is related to A. arvensis and A. placomyces, more closely to the former. It occurs during mid-summer and early autumn. Figure 10 is from plants (No. 1986 C. U. herbarium) collected in open woods at Ithaca.

Plate 4.—Agaricus placomyces. Figure 21.—Upper view of cap, side view of stem. Figure 22.—Under view of plant showing radiately torn under side of the double veil. (¾ natural size.) Copyright.

Plate 5, Figure 23.—Agaricus placomyces. Three different views, see text for explanations. Dark scales on cap. (Natural size.) Copyright.

Agaricus (Psalliota) subrufescens Pk. Edible.—The Agaricus subrufescens was described by Dr. Peck from specimens collected on a compost heap composed chiefly of leaves, at Glen Cove, Long Island. It occurs sometimes in greenhouses. In one case reported by Peck it appeared in soil prepared for forcing cucumbers in a greenhouse in Washington, D. C.

According to the description the pileus becomes convex or broadly expanded, is covered with silky hairs and numerous minute scales. The color is whitish, grayish or dull reddish brown, the center being usually smooth and darker, while the flesh is white. The gills change from white to pinkish and blackish brown in age. The stem is long, nearly cylindrical or somewhat enlarged or bulbous at the base, first stuffed, then hollow, white. The annulus is thick, and the under side marked by loose threads or scales.

This plant is said to differ from the common mushroom (A. campestris) in the more deeply hemispherical cap of the young plant, the hollow and somewhat bulbous stem, and in the scales on the under side of the annulus. In fresh plants the flesh has also a flavor of almonds. It is closely related to A. silvaticus Schaeff., p. 62, T. 242, Icones Fung. Bav. etc., 1770, if not identical with it. A. silvaticus has light ochraceous or subrufescent scales on the cap, a strong odor, and occurs in gardens as well as in the woods.

Agaricus (Psalliota) fabaceus Berk., was described in Hooker's London Journal of Botany, 6: 314, 1847, from specimens collected in Ohio. The plant is white and is said to have a strong but not unpleasant odor. Agaricus amygdalinus Curt., from North Carolina, and of which no description was published, was so named on account of the almond-like flavor of the plant. Dr. Farlow suggests (Proc. Bost. Soc. Nat. Hist. 26: 356–358, 1894) that A. fabaceus, amygdalinus, and subrufescens are identical.

Agaricus (Psalliota) placomyces Pk. Edible.—The flat-cap mushroom, Agaricus placomyces Pk., occurs in borders of woods or under trees from June to September. According to Peck it occurs in borders of hemlock woods, or under hemlock trees. At Ithaca it is not always associated with hemlock trees. The largest specimens found here were in the border of mixed woods where hemlock was a constituent. It has been found near and under white pine trees in lawns, around the Norway spruce and under the Norway spruce. The plants are from 5–15 cm. high, the cap from 5–12 cm. in diameter, and the stem 6–8 mm. in thickness.

The pileus when young is broadly ovate, then becomes convex or fully expanded and flat in age, and is quite thin. The ground color is whitish, often with a yellowish tinge, while the surface is ornamented with numerous minute brownish scales which are scattered over a large part of the cap, but crowded or conjoined at the center into a large circular patch. This gives to the plant with its shapely form a beautiful appearance. In the young stage the entire surface of the pileus is quite evenly brown. As it expands the outer brown portion is torn asunder into numerous scales because the surface threads composing this brown layer cease to grow. These scales are farther apart toward the margin of the cap, because this portion of the cap always expands more than the center, in all mushrooms. The gills are at first white, or very soon pink in color, and in age are blackish brown. Spores 5–8 × 3–4 µ.

The stem is nearly cylindrical, hollow or stuffed, white or whitish, smooth, bulbous, and the bulb is sometimes tinged with yellow. The veil is very handsome, and the way in which the annulus is formed from it is very interesting. The veil is quite broad, and it is double, that is, it consists of two layers which are loosely joined by threads. In the young stage the veil lies between the gills and the lower two-thirds of the stem. As the pileus expands the lower (outer part) layer of the veil is torn, often in quite regular radiating portions, as shown in Fig. 22. An interesting condition of the veil is shown in the middle plant in Fig. 23. Here the outer or lower layer of the veil did not split radially, but remained as a tube surrounding the stem, while the two layers were separated, the inner one being still stretched over the gills. It is customary to speak of the lower part of the veil as the outer part when the cap is expanded and the veil is still stretched across over the gills, while the upper portion is spoken of as the inner layer or part. It is closely related to A. arvensis, and may represent a wood inhabiting variety of that species.

Agaricus (Psalliota) comtulus Fr.—This pretty little agaric seems to be rather rare. It was found sparingly on several occasions in open woods under pines at Ithaca, N. Y., during October, 1898. Lloyd reports it from Ohio (Mycolog. Notes, No. 56, Nov. 1899), and Smith from Vermont (Rhodora I, 1899). Fries' description (Epicrisis, No. 877) runs as follows: "Pileus slightly fleshy, convex, plane, obtuse, nearly smooth, with appressed silky hairs, stem hollow, sub-attenuate, smooth, white to yellowish, annulus fugacious; gills free, crowded, broad in front, from flesh to rose color. In damp grassy places. Stem 2 inches by 2 lines, at first floccose stuffed. Pileus 1–1–½ inch diameter. Color from white to yellowish."

Figure 24.—Agaricus comtulus (natural size, sometimes larger). Cap creamy white with egg-yellow stains, smoky when older. Stem same color; gills grayish, then rose, then purple brown. Copyright.

The plants collected at Ithaca are illustrated in Fig. 24 from a photograph of plants (No. 2879 C. U. herbarium). My notes on these specimens run as follows: Plant 3–6 cm. high, pileus 1.5–3 cm. broad, stem 3–4 mm. in thickness. Pileus convex to expanded, fleshy, thin on the margin, margin at first incurved, creamy white with egg yellow stains, darker on the center, in age somewhat darker to umber or fuliginous, moist when fresh, surface soon dry, flesh tinged with yellow. The gills are white when young, then grayish to pale rose, and finally light purple brown, rounded in front, tapering behind (next the stem) and rounded, free from the stem, 4–5 mm. broad. Basidia clavate, 25–30 × 5–6 µ. Spores small, oval, 3–4 × 2–3 µ, in mass light purple brown. The stem tapers above, is sub-bulbous below, yellowish and stained with darker yellowish threads below the annulus, hollow, fibrous, fleshy. The veil whitish stained with yellow, delicate, rupturing irregularly, portions of it clinging to margin of the pileus and portions forming a delicate ring. When parts of the plant come in contact with white paper a blue stain is apt to be imparted to the paper, resembling the reaction of iodine on starch. This peculiarity has been observed also in the case of another species of Agaricus. The species is regarded with suspicion by some. I collected the plant also at Blowing Rock, N. C., in September, 1899. The caps of these specimens measure 4 cm. in diameter.

Agaricus diminutivus Pk., is a closely related species. It is distinguished chiefly by its somewhat larger size, and purplish to reddish brown hairs on the surface of the pileus, and by the somewhat larger spores, which, however, are small. I have found it at Ithaca, the surface of the pileus hairy, with beautiful, triangular, soft, appressed, purplish scales.