The North American species of Psathyrella.

1972]

PSATHYRELLA

19

where an occasional pseudocystidium occurs. In general, and as one would
expect, the hyphae near the gill edge are less inflated than those farther toward
the gill attachment to the pileus. In species showing strong color in the hyphal
walls (in KOH), the color is less pronounced near the gill edge. A number of
species have numerous cheilocystidia with yellow walls, and in some of these
this pigmentation (in KOH) extends to the tramal hyphae near the edge.
The flush of rose-color in certain species, such as P. gracilis, may possibly
be associated with this KOH reaction but definitely is not always so. The
pigment as seen in fresh material occurred within the cells as well as between
them in the areas where it developed, and was diffuse in water mounts.
The Trama of the Pileus. The above observations on the lamellar trama apply
almost equally well to the trama of the pileus. In the latter, however, there is
a distinct concentration of wall and incrusting pigments in the subcuticular
region. Here one can usually readily observe the concentration of pigment (in
KOH) on and adjacent to the cross walls of the hyphae. Psathyrella is the
only genus known to me featuring the combination of this distribution of hyphal
incrustations and their reaction in KOH, i.e. the incrusting material disappearing
as the pileus matures and ages. As one would expect, this varies in degree
between species, but in my estimation is to be regarded as an important generic
character.
In the pileus as well as in the lamellae, the degree of cell-inflation varies
with the species, usually being greatest in those more delicate, such as P. atomata
or P. typhae. It may be said of Psathyrella as a genus that the trend in evolution
is for the individual species to use less and less organic substance in the framework
of the basidiocarp. Hence those with small basidiocarps are generally to be
regarded as more advanced toward the direction of Coprinus than the larger
species. Certainly it is truly remarkable how little substance the basidiocarps
of species in subgenus Psathyrella contain. The reduction in substance appears
to be correlated with the degree to which the hyphal cells inflate, but is further
correlated with the reduction in the number of hyphae involved. It would be
interesting to study mycelial growth in terms of grams of mycelium produced
in relation to the weight of the basidiocarps produced and correlate both with
the weight and number of spores produced to determine, if possible, the quantitative relationships in an attempt to establish a "reproductive" factor as an indicator
of efficiency in matters of survival. Perhaps some day in a genus like Psathyrella
some meaningful estimates can be arrived at.
The cuticle of the pileus in Psathyrella is described as cellular but at least
three conditions are represented and they are intergrading to the point that
their use individually in taxonomy is ambiguous. First, the surface hyphae may
be composed of short inflated cells and their arrangement radial so that when
sections are cut tangential to the pileus one gets the impression of a "cellular"
layer of more or less isodiametric cells covering the interwoven hyphae of the
subcuticular region. Sections cut radial to the pileus, of course, will quickly
orient the observer as to the true condition. This layer may be 1-3 hyphae deep.
This feature (the development of the cuticle) is of some importance as in many
species the layer may be only one hypha deep. The opposite extreme is a
hymeniform palisade of hyphal end cells. Were it not for the intermediates,
these two types might furnish a basis for dividing Psathyrella into two genera.
As it stands, however, most species feature a cuticle 1-2 cells deep and both
types of cells are present in varying densities. A third type, reminiscent of the
Boletaceae is the trichodermial type in which the elements of the trichodermium