The North American species of Psathyrella.

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MEMOIRS OF THE NEW YORK BOTANICAL GARDEN

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are greatly inflated cells in chains of 2-4. The degree to which this type has
developed in Psathyrella needs further study. In the present work reliance has
been placed on the morphology of the layer as observed on tangential sections
of the pileus approximately midway between the pileus margin and the disc.
This degree of standardization has been found practical in the taxonomy of the
genus.
The features of the cuticular cells themselves are important enough to deserve
comment. The walls are characteristically smooth and thin, but in some species
the cells are so closely compacted that the wall between two cells seems to be
0.5 /A or slightly more thick. Usually careful observation will show a line (resembling a "middle lamella") indicating that actually two cell walls are involved
instead of one. Ordinarily this can be readily demonstrated under the low-power
oil immersion system. In some species with highly colored (in KOH) subeuticular
hyphae, the layer of cuticular cells next to the subcutis may show deposits of
pigment in the angles of the cells but it appears more as if a liquid had hardened
on the walls and in the angles rather than occurring as incrustations (possibly
arising from the breaking up of an outer wall layer, for instance). If the cuticle
is hymeniform, the pedicels of the cells often show somewhat thickened colored
walls even though the thin wall of the inflated portion appears to be hyaline.
Color, as ascertained under the microscope, however, deserves a few words of
comment at this point. First, the thinner the wall the more likely it will appear
hyaline under transmitted light. In the matter of hyaline, ochraceous, and brown
(including differentiating between rusty brown and vinaceous-brown) I could not
discern a significant difference between an apochromatic optical system and an
orthochromatic system. In using the keys in the text, therefore, either system
should work if the source of light and the filter system of the microscope do not
distort color unduly. As near as I have been able to ascertain from the species
studied to date, there are very few in which the color of the cuticular cells in
KOH or in Melzer's is significant in taxonomy. The outstanding exception is the
group containing P. tsugae and P. subalpina where the walls are characteristically
brown in KOH. In the majority of species the color ranges from hyaline to
ochraceous and if present fades on standing in the mounting medium. In a few
it may be tawny to brown but fades rapidly enough to cause one to question
its value in species recognition-too much depends on the age of the basidiocarp.
Cell content, as viewed in KOH or in Melzer's was singularly monotonous and
negative. Occasionally one finds cells with a "colloidal" content but this is
common throughout the Agaricales and as yet the only place where it might
have significance is in the boletes where such cells also give a bright orange to
red reaction.
The Stipe. The hyphae are typically elongate, thin-walled, and hyaline in
KOH, but in a few species the cross walls become brown in KOH thus forming
a striking appearance in crushed mounts. This appears to be a valuable taxonomic
feature and one deserving more detailed study to correlate data from the same
specimens fresh and when dried-especially those in which the stipe is brown or
becomes brown by late maturity.
Summary. It may be said that hyphal characters of the basidiocarp as
distinct from end cells and any tissues the latter form, are important in the
systematics of the family Coprinaceae but are of secondary importance in the
delimitation of species in Psathyrella. The features which appear to have some
importance in the taxonomy of the genus are cell inflation, KOH reaction (as
to color) on transverse septa, presence of wall thickenings and wall incrustations