Appendices & Glossary - Botanical Research Institute of Texas

COLLECTING HERBARIUM SPECIMENS/APPENDIX EIGHT
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and doing preliminary pressing there. Such a press is usually referred to as a “field press” and generally
consists only of straps, lightweight end boards, two or three cardboards, and newspapers (Fig. 181). Because
of the absence of blotters and most cardboards, a field press is much lighter than a regular press
and is thus suitable for carrying some distance in the field. Specimens pressed in this way can later be
rearranged (leaves flattened, etc.) before being put between blotters and cardboards for final pressing
and drying. However, instead of using a field press, practicality sometimes dictates that plastic bags be
used to transport the plants back to a car, kitchen table, laboratory, etc., for pressing. We have found
that carrying a number of large zip-type bags (which can be reused) inside a plastic trash bag works
well. Plants collected in this way and sprinkled with water can often be stored overnight in the plastic
bag in a refrigerator with little loss of quality. In the past, botanists temporarily stored specimens in a
metal container (called a vasculum) in folds of wet paper.
The pressing process begins by putting the plant in a single half-sheet of newspaper (22" 14")
folded crosswise (the folded half-sheet of newspaper should thus measure 11" 14"). While this size
may seem arbitrary, all subsequent steps in the collecting/herbarium process are tied to this size—
these include plant dryers, cardboards and blotters for drying, specially designed herbarium storage
cases, certain size shipping boxes, etc. The leaves, flowers, and other structures should be arranged in
as natural a manner as possible on the newspaper, while at the same time trying to avoid excessive
overlap. Folding or bending the plant is often necessary, as is the trimming off of excess material.
When trimming is done (e.g., excess leaves removed), it should be carried out in a way that makes it
clear that material was removed (e.g., a portion of the petiole of a removed leaf should be left). In order
to insure the best possible results, delicate structures such as flowers can be given additional padding
with small pieces of blotter or pads made of folded pieces of newspaper or paper towels. Another consideration
is that leaves should be arranged so that both surfaces can be seen (hair characters of the
lower surface are often important); likewise, all parts of the plant, especially reproductive structures,
should be accessible for study. At least some flowers should be spread open so that the internal structures
will be visible for examination. A number (corresponding to a number in a collecting notebook)
is written on the lower corner of the half-sheet of newspaper on the left edge or bottom adjacent to the
folds. Permanent, bold red felt-tip markers are very handy for marking newsprint. An absorbent felt or
thick paper blotter is then placed on each side of the fold of newspaper containing the specimen, and
this “sandwich” is placed between two pieces of corrugated cardboard. Additional plants are treated in
the same fashion until all have been put in the press. The result is the following sequence: cardboard,
blotter, fold of newspaper with plant, blotter, cardboard, blotter, fold of newspaper with plant, etc. (Fig.
181). While it may at first seem a waste of space, specimens of only one species should be placed in
each fold of newspaper—this prevents getting “mixed collections” that are often confusing. It is also
necessary to treat each species separately because, as discussed below, it is important to accurately
record detailed written information about each one. After the plant material has been placed in newspaper
between blotters and cardboards, wooden (or other stiff material) end boards are put on each
side of the entire stack and straps are used to apply pressure, thus “pressing” the plants (Fig. 181). In this
manner, as the plants dry they do not shrivel and high quality specimens can be obtained. The blotters
wick moisture away from the plants and the corrugations in the cardboards allow water to easily escape
the press. Some botanists use only cardboards (no blotters), with little loss of specimen quality;
this is frequently done when the weight of the press is an important consideration or when a source of
blotters is not available. In order to speed the drying process (a necessity in humid areas such as many
places in the tropics), a heat or forced air source is often necessary. An easy way to heat a press is to
leave it in the back seat or trunk of a car. A car roof rack is also an excellent place for a plant press. Plant
dryers utilizing light bulbs as a heat source are easy and inexpensive to build and are often used by
professional botanists; however, care should be taken to avoid the danger of fire (Fig. 181). Thick materials
(e.g., fruits, very thick stems, material of plants such as cacti) may be sliced in order to allow appropriate
drying and to prevent unwieldy structures in the press.
Plants should stay in the press until they are dry. The time necessary is quite variable, depending on
whether a heat source or forced air source is used, the type of plant, the humidity of the ambient air,
etc. If any part of the plant is moist to the touch, it needs additional drying. Removing plants too