The North American species of Psathyrella.

16

MEMOIRS OF THE NEW YORK BOTANICAL GARDEN

[VOL. 24

palisade. It is to be supposed, also, that there are basidium-like cells which,
genetically, are not destined to function as basidia. In looking at the hymenium
under a microscope, however, one cannot separate one kind from the other.
The term basidiole is applied to both since the morphology is that of the immature
basidium. In Psathyrella, however, there are many species in which nearly all
of the "basidioles," by the time the hymenium is mature, enlarge to globose or
elliptic in shape (in optical section) and hence are morphologically different
from young basidia which are clavate. Such enlarged cells are here termed
brachybasidioles and it is interesting to note, again, that these have reached
a high degree of development in Coprinus, adding to the morphological specialization of the hymenial elements. Their function in the hymenium appears to be
to form a cellular pavement for the support of the basidia. Although the development of brachybasidioles is a most important feature in the systematics of the
family Coprinaceae, it turned out to be impractical to use its presence in a
major way in the taxonomy of Psathyrella. First, there is no single line of
development in Psathyrella featuring the differentiation of brachybasidioles.
They appear in most of the sections here recognized, but are most frequent in
subgenus Psathyrella, the group most similar to Coprinus. Secondly, their
differentiation in Psathyrella is often delayed until full maturity of the hymenium
or later, so that in basidiocarps younger than those indicated, they cannot be
demonstrated conclusively. Also, and this is a practical consideration in Psathyrella, they often revived very poorly and this makes their presence in specimens
dried 25-100 years almost impossible to demonstrate. Consequently, in spite of
their general phylogenetic significance, I gave up trying to base a section upon
them in subgenus Psathyrella.
Cystidia. These cells differ from basidia, basidioles and brachybasidioles in
that they occur more or less at random in the hymenium and are not a basic
element as are the other structures just mentioned, i.e., one finds many species
featuring a lack of cystidia in the Agaricales as an order. In keeping with my
plan from previous works (Smith, 1947) cystidia on the face of the gill are
termed pleurocystidia, those on the edge of the gills cheilocystidia, and those on
the stipe caulocystidia. If cystidioid cells occur randomly on the pileus they are
termed pileocystidia. All are end cells of hyphae or hyphal branches. As a rule
they are much larger than basidia (at least in Psathyrella) and are characteristically fusoid-ventricose in shape (Fig. 71).
Cystidia may also be classified according to type: Those shown in Fig. 71
are termed leptocystidia and feature thin, smooth walls. Thick-walled cells
(Fig. 459) have been termed lamprocystidia (or metuloids), but in Psathyrella
one finds many species with cystidial walls of intermediate thickness to the
degree that the terms can be applied to advantage only to the extremes. In the
following descriptions the term pleurocystidium is used since it is necessary
to describe the morphology of the cell anyway. The function of these cells
is not too clearly known, but it is assumed that they are evaporating agentspossibly keeping the humidity high in the region where the young basidiospores
are forming. This could account for some of the deposits one observes over
the upper part or over the apex of many cystidia. As to wall thickenings, it
may be worthy of note that in a number of species of subgenus Pannucia there
is a slight thickening in the wall from the base to near the apex and the wall
in the apical region is thin and less refractive under transmitted light than is
the remainder. In these cystidia the thin-walled apical portion may revive much
more slowly than the remainder and more frequently carries granular deposits.