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..
Boletus luteus Linn. (B. subluteus Pk.) This species is widely distributed in Europe and America, and grows in sandy soil, in pine or mixed woods or groves. The plants are 5-8 cm. high, the cap 3-12 cm. in diameter, and the stem 6-10 mm. in thickness. The general color is dull brown or yellowish brown, and the plants are slimy in moist weather, the stem and tubes more or less dotted with dark points. These characters vary greatly under different conditions, and the fact has led to some confusion in the discrimination of species.
The pileus is convex, becoming nearly plane, viscid or glutinous when moist, dull yellowish to reddish brown, sometimes with the color irregularly distributed in streaks. The flesh is whitish or dull yellowish. The tube surface is plane or convex, the tubes set squarely against the stem (adnate), while the tubes are small, with small, nearly rounded, or slightly angular mouths. The color of the tubes is yellowish or ochre colored, becoming darker in age, and sometimes nearly brown or quite dark. The stem is pale yellowish, reddish or brownish, and more or less covered with glandular dots, which when dry give a black dotted appearance to the stem. In the case of descriptions of B. luteus the stem is said to be dotted only above the annulus, while the description of B. subluteus gives the stem as dotted both above and below the annulus.
Boletus luteus. Cap viscid when moist, dull yellowish to reddish brown, tubes yellowish stem punctate both above and below the annulus (natural size). Copyright.
The spores are yellowish brown or some shade of this color in mass, lighter yellowish brown under the microscope, fusiform or nearly so, and 7-10 x 2-4 µ. The annulus is very variable, sometimes collapsing as a narrow ring around the stem as in Fig. 173, from plants collected at Blowing Rock, N. C, September, 1899 (5. sub-luteus Pk.), and sometimes appearing as a broad, free collar, as in Fig. 174. The veil is more or less gelatinous, and in an early stage of the plant may cover the stem as a sheath. The lower part of the stem is sometimes covered at maturity with the sheathing portion of the veil, the upper part only appearing as a ring. In this way, the lower part of the stem being covered, the glandular dots are not evident, while the stem is seen to be dotted above the annulus. But in many cases the veil slips off from the lower portion of the stem at an early stage, and then in its slimy condition collapses around the upper part of the stem, leaving the stem uncovered and showing the dots both above and below the ring (B. subluteus).
An examination of the figures of the European plant shows that the veil often slips off from the lower portion of the stem in B. luteus, especially in the figures given by Krombholtz, T. 33. In some of these figures the veil forms a broad, free collar, and the stem is then dotted both above and below, as is well shown in the figures. In other figures where the lower part of the veil remains as a sheath over the lower part of the stem, the dots are hidden. I have three specimens of the B. luteus of Europe from Dr. Bresadola, collected at Tren-to, Austria-Hungary : one of them has the veil sheathing the lower part of the stem, and the stem only shows the dots above the annulus; a second specimen has the annulus in the form of a collapsed ring near the upper end of the stem, and the stem dotted both above and below the annulus; in the third specimen the annulus is in the form of a broad, free collar, and the stem dotted both above and below. The plants shown in Fig. 174 (No. 4124, C. U. herbarium) were collected at Blowing Rock, N. C, during September, 1899. They were found in open woods under Kalmia were the sun had an opportunity to dry out the annulus before it became collapsed or agglutinated against the stem, and the broad, free collar was formed. My notes on these specimens read as follows: "The pileus is convex, then expanded, rather thick at the center, the margin thin, sometimes sterile, incurved. In color it runs from ecru drab to hair-brown with streaks of the latter, and it is very viscid when moist. When dried the surface of the pileus is shining. The tubes are plane or concave, adnate, tawny-olive to walnut-brown. The tubes are small, angular, somewhat as in B. granulatus, but smaller, and they are granulated with reddish or brownish dots. The spores are walnut brown, oblong to elliptical, 8-10 x 2-3 µ. The stem is cylindrical, even, olive yellow above, and black dotted both above and below the annulus.
Plate 62, Figure 174
Boletus luteus. Cap drab to hair-brown with streaks of the latter, viscid when moist, tubes tawny olive to walnut-brown, stem black dotted both above and below the broad, free annulus (natural size). Copyright.