North American species of Mycena.

266 NORTH AMERICAN SPECIES OF MYCENA

were not seen. The cheilocystidia, which are quite numerous, measure 26-34 X 8-12 gu and are clavate; their apices are covered with
scattered short rodlike projections. The gill trama is homogeneous.
The pileus trama is very distinctive. The surface of the pileus is
covered with a very thin layer (one hypha L in thickness) of nongelatinous hyphae, the walls of which give off numerous short rodlike
projections. Beneath this is a broad layer of gelatinous hyphae
almost half the thickness of the cap. Below the gelatinous layer is a
region of enlarged cells which have smoky-brown contents (this layer
would ordinarily be the hypoderm), the trama next to the subhymenium is filamentous, but only a thin layer is present, and the subhymenium is not gelatinous. The gill edges do not gelatinize, and
there is no gelatinous layer over the stipe. Iodine reactions were not
obtained.
I have one small collection from Lake Timagami, Ontario, which
may be this species. However, it lacked an alkaline odor. Mains
(32-121) has one collection from Rock River, Michigan, which also
appears to belong here, but he did not note the odor. Numerous
collections of a small Mycena from around Mt. Baker, Washington,
also apparently should be referred here, but they did not have a very
distinct gelatinous layer beneath the pellicle. In fact, it could be
demonstrated only from dried material revived in KOH. These
collections also lacked a distinctive odor. Overholts, 18792, found
what appears to be the typical form of this species in Colorado. The
following are his notes:
"Pileus 3-8 mm. broad, campanulate, 'neutral gray' to pallid
neutral gray, pruinose to glabrous, dry, striate almost to apex, flesh
tough, thin, whitish, somewhat alkaline; gills adnexed or free, distant,
1 mm. broad, unequal, white; stipe central, terete, equal, white (at
least at apex), glabrous above, with a few white hairs, hollow, 3-4 cm.
long, 0.5-1 mm. thick; spores white, 6-7 X 3-4 A-."
The collection was meager, but the caps I sectioned had a gelatinous layer like those from around Mt. Baker. The cheilocystidia
were typical. M. pusilla is closely related to M. constans, but differs
in having a rather thick pellicle that in wet weather causes the cap
to be subviscid. This is quite a contrast to the thick gelatinous layer
beneath the pellicle of M. constans. The gills of the latter were
described as uncinate, whereas those of M. pusilla are rather broadly
adnate and, though more ascending, somewhat resemble those of
M. latifolia.