North American species of Mycena.

INTRODUCTION

3

almost always furnished with short protuberances or with the ends
straightened to form numerous hairs. Stipe central, cartilaginous,
more or less fistulose, with the base frequently bristling with-rhizoids,
the fundamental hyphae often containing numerous nuclei. Lamellae confluent with the flesh of the pileus, thin, often ascending
and more or less adnate, more rarely arcuate-decurrent; medial strand
regular or interwoven; subhymenium ramose, generally thin, lacking
calloses at the transverse walls or these not strongly basophile; basidioles cylindric, the nuclei superposed; mature basidia more or less
clavate, the fusion nucleus characteristically undergoing three successive divisions in the normal form; cystidia almost always present,
smooth or roughened. Spores white in mass or rarely tinged yellowish (latter observation by R. Maire), smooth or nodulose, almost
always with a thin wall, generally uninucleate in four-spored forms.
Saprophytic species habitually epiphytic or lignicolous.
The definition adopted in the present work is as follows: Stipe
cartilaginous, tubular or hollow, glabrous or appressed-fibrillose;
pileus variously shaped but usually conic or convex, margin usually
straight and appressed against the stipe when young but sometimes
incurved at first, fragile, fleshy, or somewhat cartilaginous in consistency but hardly reviving when remoistened (M. corticola excepted), usually membranous to submembranous; lamellae usually
ascending-adnate or hooked, often arcuate and occasionally decurrent
(if decurrent, the margin of the pileus not incurved); spores white
in deposit, thin-walled, smooth, falsely echinulate (see Fayodia), or
nodulose, amyloid reaction either positive or negative; cystidia usually
present, at least on the gill edges though often embedded and difficult to locate; gill trama usually interwoven; pileus trama characterized by some differentiation either of the hyphae of the cuticle or
of those beneath it.
As one can readily see, this definition is somewhat broader than
that of Fries and, in addition, places emphasis on microscopic characters. Certain species formerly included in Collybia and Omphalia
are here transferred to Mycena. Those with an incurved margin
and white or bright-colored pigments (in contrast to the gray, brownish-gray, bluish-gray, or black forms) are admitted to Mycena if
cheilocystidia are present and the gills are adnate. If the gills are
decurrent and the cap margin is incurved at first, the species are retained in Omphalia, provided the stipe is not viscid. The latter
look like small species of Clitocybe and have their relationships with