Teaching People Plant Collecting

Activity #3

How to Make a Scientific
Plant Collection

OBJECTIVE: Students 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 Activity #4).

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

Evaluation

The University of Arizona
Department of Biochemistry and Molecular Biophysics
General Biology Program for Secondary Teachers
warder@email.arizona.edu