Plant Collecting & Mounting Guidelines
by Collection Assistant Meg Burroughs
Plant specimens are ready to be mounted after they have been pressed, dried, identified, frozen, and labeled with their collection data (see Collecting Guidelines).
Plants are mounted to 11.5" x 16.5" archival herbarium paper, for support and to facilitate handling and preservation. The museum uses water-based white adhesive glue. This type of glue is completely reversible and cost effective.
The mounting process begins with the label, which is always glued fully to the bottom right corner of the herbarium sheet. Any annotation labels are glued fully when possible and placed directly above the collection data label. The upper right corner is reserved for the museum name and the plant accession number. These two restricted areas often limit plant placement and fitting of the specimen or specimens in the limited space. Plant placement is facilitated with the use of a mock herbarium sheet that can be used over and over again so as to prevent the archival paper from being soiled. A mock herbarium sheet may be made from a species cover cut to 11.5" x 16.5" with the restricted areas blocked out. This allows for preparatory work such as trimming or soil removal, and for finding the best angle for vegetative, floral, or fruit part(s) before the final gluing. (photo)
Displaying all aspects of the plant is important (photo). Care must be taken to represent the variety of features present, such as leaf size, leaf shape, and leaf arrangement. As far as possible make sure each specimen shows the range of flowered and/or fruit stages present. Flowers as well as fruits should face front and back when possible, or be placed in a packet. Reproductive parts also need be shown and at least one leaf should be turned over to show the underside. Roots are also a key to identification and often need to have dirt brushed away with natural bristle brushes used just for that purpose. Any seeds or loose plant fragments are placed in a folded paper packet and glued to the sheet, most often in the upper left area. At times, small resealable bags are used to contain tiny parts and are used inside packets, which come in various sizes. Large fruits are filed separately and indicated as such on the main label. A common cafeteria tray is used to hold the adhesive, which is about the same size as a herbarium sheet and will accommodate most plants. The glue is spread on a tray with a natural bristle brush to cover the surface and diluted with as little water as possible to obtain the best mixture suited for each type of plant.
First the label is glued in place. Then the plant is put directly in the glue, and the leaves and stems are gently pressed with a tool to make sure they have contact with the adhesive (photo). The plant is lifted from the glue with tweezers (forceps) and placed on the herbarium sheet in the predetermined arrangement (photo). Paper towels blot any excess glue, and a sheet of waxed paper is added to protect the upper surface. A corrugate (pressing cardboard) is added as a cushion between layers and to aid in drying. The process then begins again with the next herbarium sheet.
Various weights are used to press the mounted specimens until dry (photo). Large weights press a stack of newly mounted specimens, while loosely filled sandbags of various sizes are used on top of the waxed paper when an individual specimen is both bulky and flat. Small flat metal weights, covered in a plastic tape to prevent rust, are also used.
After drying overnight, the stacking process is reversed. The weights are removed along with the cardboard and the waxed paper. Both the cardboard and waxed paper may be reused. Each dry specimen is then carefully examined. If any repair is needed the specimen is put aside and filed back into the bundle after repairs have been made. Plants are placed back into a species cover, gently tied, and put in the freezer for several days to assure that they are contamination free. (photo)
Strapping is done by volunteers and is the last step in the mounting process (photo). During strapping, adhesive is drawn across parts of the specimens at intervals to hold loose stems or leaves. Dots of glue are also used on edges of leaves or stems to assure firm attachment.
A final freezer placement for several days is made before specimens are added to the database and then filed with the more than 600,000 specimens in the museum's permanent collection.