How to Make a Scientific
will learn how plant specimens are pressed, mounted and labeled by observing
several herbarium specimens of preserved plants. Students will then
work in groups of two to construct their own plant presses from materials
that have already been cut to size by the teacher.
NOTE: Do not expect students to cut the materials
for the plant press unless you have a large table-type paper cutter
and plan to make a lesson out of measuring and cutting.
BACKGROUND: When scientists preserve a specimen
of a plant (or part of a plant) they usually flatten it, dry it, and
mount it on special paper. Preserved in this way the plant specimen
can be stored for many years without falling apart.
Students need to be taught to select specimen material
that clearly represents the plant they are collecting. Picking a few
leaves or flowers usually does not give a representative picture of
a plant. Pieces of specimen plant material need to be large enough to
show the characteristics of normal growth and development. Taking a
branch, stem or even the entire plant may be required to get a good
specimen. Plants that show unnatural growth, damage or deterioration
will not be good specimens when dried and mounted. Stress the need
to collect good specimens.
Once a good specimen is collected, the specimen is flattened in a plant
press. A plant press is made of newspapers, cardboard, blotter paper
and wood and is held together with two straps.
Out in the field students may experience some difficulty placing plants
in the plant press, especially on a windy day. Some of these problems
can be controlled by leaving the press in a sheltered place and bringing
the plant specimens to the press. Or, the press can be left in the classroom
and plants can be brought back from the field in plastic or paper bags.
Note: It is very important that collection data be kept with
each separate plant specimen. If the plant is not placed directly
in the press at the collection site, care must be taken that the correct
information is recorded and attached to the plant specimen (see
MATERIALS FOR A PLANT PRESS
The top and bottom boards for a plant press
should be precut from one-quarter inch plywood slightly larger than
a folded section of a newspaper; cut 2 boards about 30.5 cm X 40.5 cm
(12 X 16 inches) for each press. Cardboard and blotter paper should
also be cut to the same size. Note: before cutting anything,
measure the folded newspaper that will be used in the press. Newspapers
vary in size, so measure first.
The press is then assembled by layering the newspapers, blotters, and
cardboard. There is no rule for how many of each to use. Usually 5-10
pieces of cardboard and blotter paper are interspaced with three or
four pieces of newspaper. Some plant collectors prefer to keep the newspapers
separate until a piece is needed. When a specimen is collected it is
placed in the folded newspaper and slipped between blotters into the
press. The press is held together by two straps with friction buckles.
The next page Student
Activity Sheet 3a shows students how the plant press is assembled.
Additional information on drying plant specimens is found in Making
Sure Specimens Dry