North American species of Mycena.

DIAGNOSTIC CHARACTERS

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vived in KOH. In such mounts the pellicle swells appreciably and
has a characteristic translucent appearance. Since a gelatinous
pellicle is usually readily separable from the pileus, one must be
careful not to tear it off when cutting sections.
The hypoderm, when present, usually lies next to the pellicle, but
it is not characteristic of all Mycenae. In a vertical section of a
pileus it can be seen as a layer one or several cells thick in which the
hyphae are much larger than those forming the remainder of the
flesh. There are all degrees of differentiation of the hypoderm. In
some it can be recognized only with difficulty, whereas in others it
occupies most of the thickness of the pileus, the filamentous trama
then being reduced to a narrow band. Gelatinous layers of narrow
hyphae, even though they may occur just beneath a nongelatinous
pellicle, are not classified as hypodermal tissue. In such forms, if a
hypoderm is present, it will be found beneath the gelatinous layer.
Gelatinous layers which occur in the tissue of the pileus instead of
on the surface are very important taxonomically. These can be
observed only with the aid of a microscope.
Iodine Reactions of the Flesh
Iodine reactions, which have been used by recent investigators
as a rather important character, have been included in this study.
The examinations must be made from dried material, and for this
reason the reactions are most useful to the specialist. They are often
weak, however, and are interpreted with some difficulty. A positive
amyloid reaction for the tissue of the pileus and gills is not the same
as one for the spores. These tissues turn a dark vinaceous red or
almost purple in a good positive reaction and remain hyaline or become yellowish to dull brown in one that is negative. Gelatinous
layers remain hyaline or become faintly yellowish. According to my
experience, a positive reaction may be distinctive only in limited
areas, or be weak and inconclusive throughout. In many species the
tissue of the stipe will give an exceedingly strong positive reaction.
Viscidity of the Stipe
Viscidity of the stipe has been used to distinguish a subgenus of
Mycena. It can be ascertained by means of a microscopic study of
dried specimens almost as easily as from fresh material. Cross sections of the stipe of a viscid species show the usual fundamental and