North American species of Mycena.

76 NORTH AMERICAN SPECIES OF MYCENA

a moderately long stipe, but this, according to my experience, is not a
common occurrence.
In northern California I have collected a form (8174) on redwood
twigs which is watery white, or merely tinged very pale watery gray
around the disc, and which fades to a dead white. Its cheilocystidia
are 40-54 X 10-16 /, clavate with the neck elongated, or with several
long fingerlike projections arising from the apex. Its spores are 7-9
(10) X 4-5 1A. I have but one collection and, as yet, insufficient data
to dispose of it satisfactorily. It appears to be very close to M. subcana and may be only a chance pale variation. I have observed
similar variations for such well-known species as M. megaspora.
SECTION DEMINUTIVAE
As is to be expected, a section based on size or stature of the fruiting body is almost certain to be artificial. The present grouping,
however, is much less artificial than one might suppose. In the
series of small white species we find three groups which appear quite
distinct but, nevertheless, are closely related. The first is distinguished by the absence of cheilocystidia. The other two are distinguished by the presence of cheilocystidia, which are smooth in one
and clavate-roughened in the other. These groups intergrade with
the white species of the section Adonidae. Here, as in the Adonidae,
no sharp distinction exists between Mycena and Omphalia. For
practical purposes I have included in the key most of the American
species of both groups. The only forms omitted are those that resemble small species of Clitocybe, that is, have an inrolled margin
and truly decurrent gills.
The small white species grouped here are among the most difficult
to work with that I have found anywhere in the Agaricaceae. The
difficulty rests largely in obtaining enough specimens in a single
locality to characterize the species in question. One cannot, or certainly should not, pick up scattered fruiting bodies during the course
of a days' collecting and consider them all to belong to one species
simply because they look alike and have the same microscopic characters. The iodine reaction of the spores must also be obtained, and
that can be done only on dried specimens. It is very seldom that
one finds fruiting bodies with such distinctive microscopic characters
that he can describe a species from a small number of carpophores.
M. setulosa, however, is such an example.