This section is from the book "Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc.", by George Francis Atkinson. Also available from Amazon: Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc..
The genus Bolbitius contains a few species with yellowish or yellowish brown spores. The plants are very fragile, more or less mucilaginous when moist, usually with yellowish colors, and, what is the most characteristic feature beside the yellowish color of the spores, the gills are very soft, and at maturity tend to dissolve into a mucilaginous consistency, though they do not deliquesce, or only rarely dissolve so far as to form drops. The surface of the gills at maturity becomes covered with the spores so that they appear powdery, as in the genus Cortinarius, which they also resemble in the color of the spores. In the mucilaginous condition of the gills the genus approaches Coprinus. It is believed to occupy an intermediate position between Coprinus and Cortinarius. The species usually grow on dung or in manured ground, and in this respect resemble many of the species of Coprinus. Some of the species are, however, not always confined to such a substratum, but grow on decaying leaves, etc.
This plant was found abundantly during May and June, 1898, in a freshly manured grass plat between the sidewalk and the pavement along Buffalo street, Ithaca, N. Y.
Bolbitius variicolor. Cap viscid, various shades of yellow, or smoky olive; gills yellowish, then rusty (natural size).
The season was rainy, and the plants appeared each day during quite a long period, sometimes large numbers of them covering a small area, but they were not clustered nor cespitose. They vary in height from 4-10 cm., the pileus from 2-4 cm. broad, and the stem is 3-8 mm. in thickness. The colors vary from smoky to fuliginous, olive and yellow, and the spores are ferruginous.
The pileus is from ovate to conic when young, the margin not at all incurved, but lies straight against the stem, somewhat unequal.
In expanding the cap becomes convex, then expanded, and finally many of the plants with the margin elevated and with a broad umbo, and finely striate for one-half to two-thirds the way from the margin to the center. When young the pileus has a very viscid cuticle, which easily peels from the surface, showing the yellow flesh. The cuticle is smoky olive to fuliginous, darker when young, becoming paler as the pileus expands, but always darker on the umbo. Sometimes the fibres on the surface of the cap are drawn into strands which anastomose into coarse reticulations, giving the appearance of elevated veins which have a general radiate direction from the center of the cap. As the pileus expands the yellow color of the flesh shows through the cuticle more and more, especially when young, but becoming light olive to fuliginous in age. In dry weather the surface of the pileus sometimes cracks into patches as the pileus expands. The gills are rounded next the stem, adnate to adnexed, becoming free, first yellow, then ferruginous. The basidia are abruptly club-shaped, rather distant and separated regularly by rounded cells, four spored. The spores are ferruginous, elliptical, 10-15 x6-8 µ, smooth. The stem is cylindrical to terete, tapering above, sulphur and ochre yellow, becoming paler and even with a light brown tinge in age. The stem is hollow, and covered with numerous small yellow floccose scales which point upward and are formed by the tearing away of the edges of the gills, which are loosely united with the surface of the stem in the young stage. The edges of the gills are thus sometimes finely fimbriate.
At maturity the gills become more or less mucilaginous, depending on the weather. Plants placed in a moist chamber change to a mucilaginous mass. When the plants dry the pileus is from a drab to hair brown or sepia color (Ridgeway's colors). Figure 158 is from plants (No. 2355 C. U. herbarium).