The boletes of Michigan, by Alexander H. Smith and Harry D. Thiers.

BOLETUS 339
Pileus 4-12 (18) cm broad, convex with the margin regular to
irregular, becoming broadly convex to depressed-convex or nearly plane;
surface dry and velvety to subtomentose, in age finally irregularly rimose
to areolate, often merely unpolished at maturity; bright yellow on the
young incurved margin, remainder dull yellow to yellow-brown ("ocheryellow" to "buckthorn-brown"), at times darker when young and then
"raw-umber" to "Dresden-brown," slowly becoming "buckthornbrown," when dried retaining these colors. Context thick, firm, yellow
but quickly changing to blue when cut, taste mild, odor none; with
KOH orange, with FeSO4 the yellow areas fading to pallid.
Tubes 1-2 cm deep, adnate becoming depressed around the stipe,
pale yellow quickly staining blue when cut; pores dark yellow-brown
("argus-brown" to "Sudan-brown"), small (about 2 per mm), bluish
bruised and staining darker brown with KOH.
Stipe 4-8 cm long, 10-25 mm thick, equal, solid, bright yellow
within but soon blue when cut; surface reticulate in apical region to
one-third the distance to the base, ground color ochraceous but this
shaded from the grayish to brownish pruina, often reddish at the base
and soon dingy brownish where handled (after the blue fades out), base
at times with a velvety covering.
Spore deposit dull olivaceous; spores (9) 11-14 (15) X 3.5-5 u,
smooth, no apical pore evident, in face view nearly oblong to slightly
ventricose, in profile slightly inequilateral with a shallow suprahilar depression, with an inconspicuous hyaline sheath, pale ochraceous to pale
tawny in KOH and not appreciably darker in Melzer's, smooth, wall
slightly thickened, no fleeting-amyloid reaction observed.
Basidia 4-spored, 17-25 X 8-10 i, short-clavate, hyaline to dingy
buff in KOH and in Melzer's. Pleurocystidia scattered, 35-55 X 9-14 i,
fusoid-ventricose, the neck often curved and apex subacute, thin-walled,
hyaline in KOH or content in part yellowish, in Melzer's often with dark
yellow-brown pigment in the neck. Cheilocystidia about like the pleurocystidia but usually narrowly fusoid-ventricose and 30-45 X 7-10 i, hyaline to yellow-brown in KOH and often darker brown revived in
Melzer's, the pigment apparently in the wall to some extent in some
pilei but regularly in the cell content.
Tube trama of gelatinous divergent hyphae with thin walls and no
incrustations (the Boletus subtype). Pileus cuticle a trichodermium of
narrow (4-7 u) hyphae with end-cells at times narrowly clavate, soon
collapsing to form a cutis of interwoven hyphae, their content golden
yellow in KOH and orange-brown in Melzer's. Clamp connections none.
No amyloid cell inclusions seen but few scattered granules present between the hyphae in some mounts.