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

TYLOPIL US

105

standing, in Melzer's weakly dextrinoid, no amyloid inclusions present;
wall up to 0.4 g thick; spore outline in exceptionally large spores tending to angularity.
Basidia 4-spored, 8-12 i in diameter, hyaline in KOH. Pleurocystidia rare, more or less fusoid-ventricose, 33-47 X 9-15 A, apex acute
to subacute, content dull brown in Melzer's, hyaline or nearly so in
KOH (after standing 20 minutes or more).
Tube trama lacking hyphae with amyloid inclusions or amyloid
walls. Pileus cuticle of interwoven hyaline hyphae 6-12 p in diameter
with long to short tubular to slightly inflated cells but mostly the cells
elongate, content hyaline in KOH, and in Melzer's ochraceous, walls thin
and lacking incrustations, end-cells merely blunt but varying in shape
from subcylindric to fusoid-ventricose. Hyphae next to cuticle merely
yellow in Melzer's. Clamp connections absent.
Observations.-The changing pileus context to blue and then blackening should distinguish T. fumosipes from T. umbrosus if the rooting base
is poorly developed. In Smith 62850 the injured context stained blue
slowly.
45. Tylopilus umbrosus (Atkinson) Smith & Thiers
Mycologia 60:950. 1968
Boletus umbrosus Atkinson, Joum. Mycol. 8:112. 1902.
Illus. Figs. 27-28.
Pileus 5-9 cm broad, convex then expanded, subtomentose, in age
becoming finely areolate, mummy-brown to walnut-brown, fleshy; flesh
whitish, very slowly changing to flesh color and then brown. Tubes
convex, white at first, then becoming pale brown, in age deeper brown,
when bruised becoming dark brown. Stipe colored like the pileus, 8-10
cm long, 1.5-2 cm thick, broadly and irregularly furrowed to rugose
longitudinally, with very minute dark points under a lens; base tapered
into a short root.
Spores 11-14 X 4.5-5.5 ju, smooth, pale in KOH but not hyaline
(the darkest a pale bister) smooth, thin-walled, lacking apical differentiation, wall cyanophyllic in young stages but not at maturity or staining
blue only slowly on standing a day or so; shape in face view elliptic to
oval and in profile subelliptic to very obscurely inequilateral (note that
in lactic acid mounts some young spores inflated to 6-7, but in KOH
or Melzer's mounts from the same hymenophore no such wide spores
were evident).