The North American species of Psathyrella.

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MEMOIRS OF THE NEW YORK BOTANICAL GARDEN

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remember that you are going to get many sections of pith in the mount along with
the sections of fungus tissue. Remove the pith with a suitable implement. Mount
sections in the various media already mentioned for the study of fresh material
and study the cells and tissues as desired. Be sure to note color differences in
spores, thickness of the cystidial walls (if thick enough to measure), and compare
this data with that obtained from fresh material. For instance, the amyloid
reaction of spore and hyphal walls is often stronger on material dried and then
revived, than on the same structures when fresh, in a given species. Never mix
the KOH with the Melzer's solution. Students are tempted to save time by making
one mount and slowly drawing the various mounting media through the mount
by adding the new medium on one side and absorbing the old medium at the
opposite side. This does not work for the combination of KOH and Melzer's.
Chemical Reactions on Fresh Material. Most work done on the fleshy fungi in
this category has been on an empirical basis. Any chemical one thought of trying
was used. It has been found, however, that certain chemicals do give apparently
constant color changes and some of these appear to indicate significant differences
between taxa. In Psathyrella, however, to date, chemicals have been found to be
relatively inactive. They have been given little importance in the present work
but deserve further study. KOH (a 2.5 per cent solution) gives certain color
changes in cystidial walls, and ammonia gives some color changes on cystidial
incrustations (Kiihner and Romagnesi, 1953). KOH also produces color changes
in spore and hyphal walls and on hyphal incrustations. The latter changes are best
seen on revived material on sections under the microscope.
Tests on the fresh context are usually made by placing a piece of context on a
glass slide and then placing the chemical on the fungus tissue. View against white
paper. If more than one chemical is being tested be sure that contamination is
avoided. Ammonia, for instance, is very volatile and the fumes by themselves
may cause a color change on a pileus. I always apply it last in a series.
MICROSCOPIC FEATURES OF PSATHYRELLA
Spores
The features of the spores are the most important of all taxonomic characters
in the genus, but taken alone do not necessarily indicate relationships between
species. The spores in Psathyrella show considerable range in diversity centered
around a central pattern which is aptly described as being monotonous relative to
both spore size and shape. This has made it necessary to standardize the descriptions so that differences and similarities are most readily apparent. As can be
seen from a glance at the descriptions, the order of treating spore characters is
roughly as follows: size (length and width, or if the spore is flattened to some
degree both the width in profile followed by the width in face view are given).
Type and degree of ornamentation is described next and then the presence (and
features) of the apical germ pore. Next, the shape of the spore in face view is
followed by the shape in profile view. In older descriptions very often when spores
were quite different in appearance in face and profile view, the differences were
merely regarded as "variation." Color in KOH and in Melzer's follows spore shape,
and lastly the thickness of the wall is given in approximate values. Generally
speaking, thickness of the spore wall in Psathyrella is about at the thickness
which cannot be measured accurately with the light microscope.
Spore size is very constant throughout the family Coprinaceae, but one must
be careful to check the number of spores borne on a basidium. It was established