The North American species of Psathyrella.

8

MEMOIRS OF THE NEW YORK BOTANICAL GARDEN

[VOL. 24

The Microscopic Features from a Study of Fresh Material: Spores. Remove
some spores from the spore deposit with a scalpel or penknife, and transfer them
to a drop of water on a microscope slide by simply washing them off. Place a
cover slip over the drop containing the spores and wipe away the surplus water.
One will always start with a drop that is too large. After a few trials, however,
one will learn how small a drop is needed to cover the area under the cover slip
without having any extra. Air bubbles in the mount can be eliminated by applying pressure on the cover slip with a tooth pick or needle. Do not use your finger
as it will leave a grease spot on the surface of the glass. When the slide made in
water is finished, make similar mounts in Melzer's reagent (see p. 443), and one
in KOH in that order. Examine the KOH mount first and note the spore color.
At first it is likely to be some shade of chocolate color, often the color of powdered
cocoa. Next examine the water mount and note the color of the spores-it may
not be the same as in KOH. Repeat the process with the slide in Melzer's. Then
go back and reexamine the KOH mount. By this time, for some species of
Psathyrella at least, the spores may have become dark chocolate color. In other
species the spores in KOH may be nearly hyaline or they slowly become so in
about 15 minutes.
Next one should closely observe the details of the spore. This is done by using
an oil-immersion lens of numerical aperture of 1.25 to 1.3 (or 1.4 if such is available). A 10 x eye-piece is also recommended. Place a drop of immersion oil on
top of the coverglass over the object to be examined and lower the objective into
the oil. Then slowly focus with the fine adjustment until the spores are sharply
defined. Use a no. 1 cover slip and a minimal amount of the mounting medium.
If there is any indication that the spore surface is not perfectly smooth repeat the
examination using the mount made in Melzer's. For details of the spore structure
and ornamentation see p. 10.
Details of the Basidiocarp. After the spores have been studied one is ready to
consider the microscopic features of the basidiocarp itself. The hymenium is
usually studied first. For this purpose cross sections of the gills are made by
cutting a wedge-shaped piece out of the pileus with 2-3 complete gills on the
under side of it. Hold the piece of tissue between the thumb and forefinger of
your left hand (if you are right-handed) in such a way that the long axis of the
gill is roughly parallel with the long axis of the thumb and with the gill tissue
extending beyond the fingers far enough so that when you cut off (and throw
away) the projecting part you are next able to cut across the gills fairly near a
point half way between the two extremities (point of attachment to stipe and
margin of the pileus). Next cut with a slicing motion to obtain the sections. These
will stick to the razor blade and should be washed off in the material in which
the mount is being made-water, KOH, or Melzer's, for instance. Tease the mass
of sections apart with the aid of a needle and place a cover slip on the mount.
It is worth while learning to make free hand sections in this manner because it
eventually saves you a great deal of time. Sections mounted in water, or in KOH,
can be studied immediately, but those mounted in Melzer's need to stand
10-15 minutes to allow the hyphal cells to revive properly. Cross sections of
the gills made in the above manner should show the hymenium (basidia and
basidioles along with pleurocystidia if such are present), see p. 16. On some of
the sections one should also note the cells forming the edge of the gills (cheilocystidia), see p. 16. The arrangement of the threads of the gill trama (the hyphae)
and the details of their cells may also be studied (p. 18). Another way of
demonstrating cheilocystidia is to mount a gill edge flat on the slide. To do this