North American species of Mycena.

TECHNIQUE AND MATERIAL

33

(illustrated in Plate 99) with electricity as the source of heat. The
frames of the racks have interchangeable parts held together by onequarter-inch bolts with winged nuts. The racks can be set up or
taken down in a few minutes, and when demounted they can be
conveniently packed in an automobile. The shelves for the specimens were built by soldering wire screening between two metal frames.
The metal frames make the shelves compact and easy to stack in the
back of a car. The screens are rather fine-meshed because specimens
shrink considerably in drying and are easily lost. The secret of the
drying process is to have a steady current of warm air (not too hot)
circulating through the piles of specimens on the shelves. The lowest
shelf is kept far enough above the source of heat to prevent it from
becoming too hot to touch. I usually put the tough woody fungi or
the pliant types like Marasmius on the lowest shelf and the watery
ones on the uppermost. Mycenae can easily be dried on any shelf.
When dry, a collection with its label is wrapped in waxed paper in the
same manner as a fresh collection and stored in a carton. When removed from the drier the specimens are very brittle, but, although
wrapped in waxed paper, they soon absorb enough moisture from the
atmosphere to make them pliant. In this condition they can be
packed tightly in cartons without danger of breakage. They are
shipped to the laboratory at frequent intervals, where they are fumigated with paradichlorbenzene and sealed up until such time as the
expedition has been completed and they can be restudied.
LABORATORY TECHNIQUE
Methods of studying herbarium specimens vary considerably
with the individual, and so I shall briefly describe those used in this
work. In the first place, microscopic studies of fresh specimens are
checked by a reexamination of the collections in the laboratory. The
procedure for studying dried specimens is as follows: The part to be
sectioned is moistened with 70 per cent alcohol to wet the surface
and drive out the air. Then it is immersed in water until it softens.
The softened material is next placed between two pieces of pith, and
freehand sections are made with a sharp razor. These are cut in
such a way as to give cross sections of the gills as well as sections
through the pileus showing the structure of the flesh. They are
mounted on a slide in a drop or two of 2 per cent KOH. If they are
to be tested with iodine, the sections are placed in a drop or two of the
reagent and allowed to stand for a short time (5-20 minutes) before