The North American species of Psathyrella.

1972]

PSATHYRELLA

17

In some species having thick-walled cystidia the apex may be ornamented with
crystals which in NH3 turn green to olive. Kihner and Romagnesi (1953)
emphasized this feature. In KOH a number of species have cystidia in which
the walls become vinaceous to vinaceous brown. These are the two most important
chemical reactions associated with cystidia in the genus, and neither is as reliable
for taxonomic purposes as one would like to have them be. In two species the
content of the cystidia (at least some of them) is amyloid.
Pleurocystidia vary greatly in size but less so in shape. Certain patterns,
however are important. Kiihner and Romagnesi (1953) used the outline of the
apex in optical section as a major character, and my investigation has supported
this evaluation. This does not mean, however, that in a given species one cannot
find both types. The significant shapes for the cystidial apex are as follows:
broadly rounded (Fig. 24), obtuse (Fig. 102), subacute (Fig. 284), and acute
(Fig. 285). For any given species, variation is likely to encompass any two
adjacent designations. In the broadly rounded type one often finds that the
apex may become spathulate (in optical section) due to a tendency to bifurcate
or to develop 1-3 protrusions which if they elongate become finger-like processes.
This tendency is readily observed in the exannulate variety of P. kauffmanii and
in P. spadiceogrisea. Their presence in P. cornifericystis suggested the species
epithet. No instance of clavate-echinulate cystidia as found in Mycena has been
observed. Size is important in a secondary way for there appears to be a
breaking point at about 50 Iu for length. Many species have typically shorter
cystidia and in some groups such as the stirps Obtusata, they are mostly longer.
Two points should be kept in mind in measuring cystidia: first, cut sections
of the gills in the usual way and then crush the sections by pressure on the cover
glass to the point of separating the cystidia from the hymenium. They may have
a narrow (2-4 / wide) pedicel that is 15-20, long. Many of these cystidia
originate in the gill trama but are not obviously connected to any laticiferous
hyphal system. Secondly, one should measure cystidia from mature basidiocarps
to be sure that they are fully elongated.
The content of the Psathyrella cystidium is monotonously homogeneous-in
water, KOH or in Melzer's, but in a few species one finds a large globule. Kiihner
and Romagnesi (1953) noted this in P. gossypina, and I have noted it in P.
fraxinophila, P. canadensis and P. delineata as commented upon in the text. In
subgenus Homophron two species have been discovered in which cystidia are
sometimes filled with refractive particles. Kiihner and Romagnesi (1953) and
Heineman (1942) noted amyloid content in P. cotonea (lacrymabunda) and P.
hispida respectively. A diligent search was made on the North American representatives of the genus but no additional species showing this feature were
discovered. No species were discovered having amyloid or dextrinoid cystidial
walls, though in a few the cystidial walls are yellow in KOH. The only generalization I am tempted to make about the cystidia in Psathyrella is that they are
monotonous in that a general pattern is followed through the genus-with some
diversity in chemical features and in the shape of the apex.
Cheilocystidia. These fall readily into two categories: those more or less
resembling the pleurocystidia morphologically, and those which are clavate to
subglobose. In the latter the walls of some, at least in many species, are ochraceous
in KOH and this may extend to the hyphae giving rise to them. Those resembling
the pleurocystidia typically are shorter than the latter due to having shorter
necks. Basidia seldom occur on the gill edge in significant numbers in Psathyrella