This last genus is apt to be confused with certain species of Boletus which have a distinct radiate arrangement of the tubes. It is questionable whether it is clearly distinguished from the genus Boletus. BOLETUS Dill. Of the few genera in the _Polyporaceæ_ which are fleshy and putrescent, _Boletus_ contains by far the largest number of species. The entire plant is soft and fleshy, and decays soon after maturity. The stratum of tubes on the under side of the cap is easily peeled off and separates as shown in the portion of a cap near the right hand side of Fig. 169. In the genus _Polyporus_ the stratum of tubes cannot thus be separated. In the genera _Strobilomyces_ and _Boletinus_, two other fleshy genera of this family, the separation is said to be more difficult than in _Boletus_, but it has many times seemed to me a "distinction without a difference." The larger number of the species of _Boletus_ grow on the ground. Some change color when bruised or cut, so that it is important to note this character when the plant is fresh, and the taste should be noted as well. =Boletus edulis= Bull. =Edible.= [_Ag. bulbosus_ Schaeff. Tab. 134, 1763. _Boletus bulbosus_ (Schaeff.) Schroeter. Cohn's Krypt, Flora. Schlesien, p. 499, 1889].--This plant, which, as its name implies, is edible, grows in open woods or their borders, in groves and in open places, on the ground. It occurs in warm, wet weather, from July to September. It is one of the largest of the Boleti, and varies from 5--12 cm. high, the cap from 8--25 cm. broad, and the stem 2--4 cm. in thickness. [Illustration: PLATE 56, FIGURE 164.--Boletus edulis. Cap light brown, tubes greenish yellow or yellowish; stem in this specimen entirely reticulate (natural size, often larger). Copyright.] The =pileus= is convex to expanded, smooth, firm, quite hard when young and becoming soft in age. The color varies greatly, from buff to dull reddish, to reddish-brown, tawny-brown, often yellowish over a portion of the cap, usually paler on the margin. The flesh is white or tinged with yellow, sometimes reddish under the cuticle. The =tubes= are white when young and the mouths are closed (stuffed), the lower surface of the tubes is convex from the margin of the cap to the stem, and depressed around the stem, sometimes separating from the stem. While the tubes are white when young, they become greenish or greenish-yellow, or entirely yellow when mature. The =spores= when caught on paper are greenish-yellow, or yellow. They are oblong to fusiform, 12--15 µ long. The =stem= is stout, even, or much enlarged at the base so that it is clavate. The surface usually shows prominent reticulations on mature plants near the tubes, sometimes over the entire stem. This is well shown in Fig. 164 from plants (No. 2886, C. U. herbarium) collected at Ithaca, N. Y.