North American species of Mycena.

24 NORTH AMERICAN SPECIES OF MYCENA

spore is characteristic of most of the section Typicae. In the series
of small white species one frequently finds subfusoid spores or the
long, narrow type (see M. gypsea and 1M1. delicatella). There does not
appear to be much correlation between shape and iodine reaction.
Those of M. paucilamellata are more or less aciculate and amyloid.
It is now generally recognized that the spores from two-spored
basidia are larger than those from four-spored individuals of the same
species and that this difference and the two-spored condition together
are not of sufficient taxonomic importance to justify the erection of
new species. The increase in spore size in two-spored forms appears
to be the result of the distribution of the contents of the basidium to
two instead of four spores. If only one spore is produced, it is much
larger than either of the pair if two are produced; if three spores are
formed, the size is usually intermediate between that of typically twoand four-spored forms. In fruiting bodies in which the various
basidia of a pileus produce one, two, three, and four spores, the collector is certain to obtain a very confusing spore deposit. Consequently, in measuring the spores of a Mycena care must be taken to
examine the basidia of the cap from which the deposit was obtained.
The character of producing two instead of the normal four sterigmata
on a basidium seems to be constant in some forms but variable in
others. Since it is found in forms in which the nuclear behavior appears to be normal as well as in the parthenogenetic forms, it cannot
be regarded as correlated with a definite type of nuclear history.
In general, the spores from four-spored and two-spored forms are
of the same shape. In M. supina, however, this is not true. In the
four-spored form they are globose or nearly so; in the other they are
broadly ellipsoid. The spores from monosporous basidia are frequently quite misshapen.
The spores are smooth in all but a few species. In the section
Nodulosae of Mycenella they are nodulose; in the section Pseudoechinulatae they appear echinulate under ordinary magnifications, but
in reality are smooth. The thickened inner wall is filled with fine
pores which create an echinulate appearance. Some investigators
recognize these two sections as distinct genera (Mycenella and Fayodia). No species with truly echinulate spores are included in Mycena.
The iodine reaction of the spore wall is another character of major
importance, but I have minimized its use in the keys as much as
possible because of the difficulty of determining it on fresh material.
It is a character of considerable value to the specialist, but one likely