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..
This species was named B. vermiculosus because it is sometimes very "wormy." This is not always the case, however. It grows in woods on the ground, in the Eastern United States. It is from 6-12 cm. high, the cap from 7-12 cm. broad, and the stem 1-2 cm. in thickness.
The pileus is thick, convex, firm, smooth, and varies in color from brown to yellowish brown, or drab gray to buff, and is minutely tomentose. The flesh quickly changes to blue where wounded, and the bruised portion, sometimes, changing to yellowish. The tubes are yellowish, with reddish-brown mouths, the tube surface being rounded, free or nearly so, and the tubes changing to blue where wounded. The stem is paler than the pileus, often dotted with short, small, dark tufts below, and above near the tubes abruptly paler, and sometimes the two colors separated by a brownish line. The stem is not reticulated. Figure 169 is from a photograph of plants (No. 4132 C. U. herbarium) collected at Blowing Rock, N. C, during September, 1899.
Boletus obsonium (Paul.) Fr. - This species was not uncommon in the woods at Blowing Rock, N. C, during the latter part of August and during September, 1899. It grows on the ground, the plants usually appearing singly. It is from 10-15 cm. high, the cap 8-13 cm. broad, and the stem 1-2 cm. in thickness, considerably broader at the base than at the apex.
The pileus is convex to expanded, vinaceous cinnamon, to pinkish vinaceous or hazel in color. It is soft, slightly tomentose, and when old the surface frequently cracks into fine patches showing the pink flesh beneath. The thin margin extends slightly beyond the tubes, so that it is sterile. The flesh does not change color on exposure to the air. The tubes are plane, adnate, very slightly depressed around the stem or nearly free, yellowish white when young, becoming dark olive green in age from the color of the spores. The tube mouths are small and rotund. The spores caught on white paper are dark olive green. They are elliptical usually, with rounded ends, 12-15 x 4-5 µ. The stem is white when young, with a tinge of yellow ochre, and pale flesh color below. It is marked with somewhat parallel elevated lines, or rugae below, where it is enlarged and nearly bulbous. In age it becomes flesh color the entire length and is more plainly striate rugose with a yellowish tinge at the base. The stem tapers gradually and strongly from the base to the apex, so that it often appears long conic.
The plant is often badly eaten by snails, so that it is sometimes difficult to obtain perfect specimens. Figure 170 is from a photograph of plants (No. 4092 C. U. herbarium) from Blowing Rock, N. C.