North American species of Mycena.

DIAGNOSTIC CHARACTERS

to be difficult for the beginner to interpret. The chief reason for this
situation lies in the fact that the various species show all degrees of
reaction from very positive to completely negative. The details of
the technique employed to determine the character are discussed
later (p. 35). In a strong positive reaction the spore becomes dark
violet, and the change is clear either in daylight or under a daylight
bulb. However, as one examines specimens in which the reaction is
weaker, it is necessary to use daylight. In a weak reaction the spores
become very pale bluish gray, and not all of them react. As Kuhner
has pointed out, groups of immature spores along the gills frequently
give a clear reaction when others fail to do so. An excellent way to
get a quantitative test is to make a spore print, preferably heavy, on
a slide, and when it is thoroughly dry, to test it with a drop of iodine
solution. If amyloid, the spore deposit will become dark or pale
gray or violet; if nonamyloid, it will remain practically hyaline or
become slightly yellowish when viewed against white paper.
Basidia
The size and shape of the basidia are of little taxonomic significance except in some of the small species, where they are relatively
obese (15-18 X 7-8 p) or relatively narrow (15-24 X 5-6,u). The
number of spores borne on a basidium is also of little help to the
taxonomist except as it applies to the spore size of one-, two-, and
three-spored forms (see the discussion on p. 24).
Cystidia
The markings, shape, and distribution of the cystidia are among
the most important characters used to distinguish species of Mycena.
A cystidium in Mycena may be defined as any sterile cell in the
hymenium or along the edges of the gills. In the dark-spored agarics,
where the paraphyses or pseudoparaphyses are often differentiated
from the basidia, this definition would not apply. The cystidia that
occur on the faces of the gills are termed "pleurocystidia"; those on
the edges, "cheilocystidia." For convenience the sterile cells projecting from the surface of the pileus are termed "pilocystidia"; those
projecting from the surface of the stipe, "caulocystidia." When
studying the pilocystidia one should be careful to distinguish between
differentiated hyphal cells and the short, often somewhat contorted
processes which arise from the walls of the hyphae forming the pellicle