The North American species of Psathyrella.

1972]

PSATHYRELLA

13

were russet (rusty brown) in 20 per cent H2S04. In P. foenisecii they were
tawny in concentrated acid and did not disintegrate. In P. hirtosquamulosa in
concentrated acid they were avellaneous. In P. jalapensis they became hyaline
immediately. In P. michiganensis, yellow, P. obtusata, hyaline, P. subrubella,
tawny, etc.
A critical study needs to be made using various concentrations of sulphuric
acid. It is obvious that different color reactions will be found, and to me at least,
a reaction which disintegrates the spore wall in a short time is too severe. In
my estimation it is significant that a brown reaction is obtained in a fair number
of species when more dilute solutions are used, and it may be possible to trace
the development of the sulphuric acid-stable wall components by this method.
Also, color reactions obtained with dilute solutions, it seems to me, are likely
to be more significant in indicating slight differences in chemical composition.
Spore shape. This is more easily described than spore color, and it can also
be illustrated. In the taxonomic treatment in this work, spore shape is described
along with the other details of the spore according to a definite plan, as previously
stated.
The simplest spore to describe is one which is terete as viewed in an imaginary
cross section. Such a cross section would be represented by a circle of the diameter
of the spore. To describe such a spore the standard terms applying to the simple
geometric figures they most closely resemble are used: ellipsoid, ovoid, globose,
etc. These apply to 3-dimensional objects. Since in Psathyrella the spore is
often of one shape in face view and another in profile, these two views are
described separately in terms of the optical section (a 2-dimensional figure). The
terms applied are elliptic, if the ends are rounded and the sides are somewhat
convex (or at least not parallel), oblong is most like elliptic but with blunter ends
and parallel or nearly parallel sides; ovate is the shape of a hen's egg, etc.
Psathyrella frustulenta has ellipsoid spores. In Psathyrella, however, very few
species have spores of the simplest shape. In most a "verbal picture" can be best
realized only by reference to more than one term, to account for variation.
The majority of species have spores which in face view are elliptic or vary
slightly from this configuration and the term subelliptic is applied to include
such deviations. I have religiously tried to avoid compound terms that are
self-contradictory such as "elliptic-fusoid." Major variations from the norm
(elliptic) are important taxonomically. One common type is described as ovate,
here defined as the outline of a hen's egg seen in optical section; in this case the
broad end of the spore is toward the attachment to the basidium. It is a simple
progression from this type to that shown in Fig. 19 for P. hirtosquamulosa in
which the spore in face view resembles in shape the flat side of a kernel of
ordinary field corn, and is so described. If the spore in face view is isodiametric,
it is to be described as circular in outline, or if almost isodiametric, subcircular.
Under no circumstances should a spore with a length-width ratio of 1-0.7 be
described as globose (3-dimensional) or circular (2-dimensional term). Psathyrella spores commonly vary enough to justify using two of the above terms to
describe them. If subglobose is the norm, the variation is likely to be to globose
or to broadly ellipsoid or both. In the descriptions the face view is often given
as elliptic to ovate, and the profile view given separately.
In my plan of presentation I have tried to give the commonest shape first
and the deviations following it, i.e., "elliptic to oblong, rarely ovate" means that
most spores are elliptic in face view but a number are oblong (less than 50 per
cent), and that a few are broadest near the base. Spores of one species may be