Collecting and preserving plants

Photo courtesy of Philadelphia's Academy of Natural Sciences Although they are nearly 200 years old, the dried leaves and flowers that Lewis collected, mounted and labeled are in remarkably good shape. This specimen is Oregon grape (Berberis aquifolium), the state flower of Oregon.

Before setting out on his epic journey across the continent, Meriwether Lewis spent several weeks in Philadelphia being tutored in medicine, botany, geology and other disciplines by the leading American scientists of the day. No doubt it was during this hurried apprenticeship that he learned the proper techniques for obtaining and preserving plant specimens.

He apparently was a good student. During the Corps of Discovery's 28-month trip from St. Louis to the Pacific and back, Lewis collected and preserved hundreds of specimens of plants he thought were interesting or believed were new to science. Although many of the specimens were destroyed accidentally (ruined by water while in storage) before they could be sent back to the East Coast, 226 of them survive today at the Academy of Natural Sciences in Philadelphia. Although they are nearly 200 years old, the specimens are generally in fine condition and are among the academy's prized possessions

The techniques for preserving and mounting plant specimens have changed little since the 1600s, when botanists and collectors first began scouring the world in search of new plants to bring back to Europe for medicinal, horticultural or scientific purposes. Botanists today, like their counterparts more than 400 years ago, collect a sample of the plant, press and dry it, and then affix it to a sheet of heavy paper. A label is attached to the sheet indicating where, when and by whom the plant was collected, giving its full Latin name, common name, and other pertinent data - the color of the flower, for example, which will fade over time. A collection of such specimen sheets is called an herbarium. Large botanic gardens often maintain herbariums containing more than a million specimens.

When properly mounted, dried plants also are aesthetically pleasing, and can be displayed like any other work of art. They also can serve as scrapbook mementos of a noteworthy trip. To emulate Lewis and assemble your own herbarium specimens, you need only a few simple tools: clippers, plastic bags, a plant press, mounting paper, and glue or tape.

The most important of these items is a plant press. Although presses are available commercially, you can make your own out of scraps of plywood, pieces of cardboard, sheets of newspaper and bungee cords.

First, cut two pieces of quarter- or half-inch plywood into rectangles. Ideally, they should be 12 by 17 inches (professionally prepared herbarium specimens are mounted on sheets 11.5 by 16.5 inches), but the press can be smaller if you don't want to deal with such an awkwardly large mount. Building a frame that's 9 inches by 12 inches allows you to use letter-size paper for your mounts, which will then fit in standard file drawers.

Cut several pieces of corrugated cardboard and sheets of newspaper the same size as the plywood. Place one piece of plywood on a flat surface, lay a sheet of card board on top, and then place a piece of newspaper atop the cardboard. Place a plant specimen on the newspaper, and then put another layer of newspaper on top of the plant. Continue sandwiching plants between sheets of newspaper, which will absorb moisture from the plant tissues, and insert a sheet of cardboard every few layers to allow air to penetrate the stack.

When you have placed all your specimens between layers of newspaper, add a final piece of cardboard and top the stack with the second sheet of plywood. Use bungee cords or straps with buckles to cinch the stack together fairly tightly. Place it in a warm, dry place for several days or a week, until the plants are dry.

Make sure that the plant is arranged in the press the way you wish it to appear when mounted, as it will be impossible after a day or two to bend the drying stems without breaking them. Botanists arrange the specimen to show the inside and outside of the flower petals, as well as the upper and lower surfaces of leaves, but collectors planning to display a plant for purely decorative purposes concentrate instead on orienting the specimen in a visually pleasing manner.

Botanists usually try to collect as much of the plant as possible - roots, stem, leaves, seeds, fruit, flowers - all of which are helpful in identifying species and genus. For display purposes, you need only those parts of the plant you find attractive. If you cannot place the plant immediately in the press, the specimen can be stored in a plastic bag for up to a day, keeping it fresh and pliable. For collecting woody or thorny plants, clippers and a pair of gloves will prove useful.

Once the plant has been pressed and dried, it can be mounted on a sheet of heavy paper or mat board (archival-quality sheets are best, because the acid in standard paper and cardboard will darken the sheet over time and stain the plant). To attach the plant to the paper, use a transparent adhesive such as Elmer's white glue, which can be thinned with water and applied directly to leaves and flowers. Small weights, such as heavy washers, nuts, nails or fishing sinkers, can be used to hold the plant in place while the glue dries. For heavier or bulkier specimens, use paper tape cut into thin strips (cellophane tape will become brittle) to strap stems securely to the paper.

When collecting, keep in mind that it is illegal to remove anything - even so much as a flower - from national park land, and that it's best to obtain owner permission before venturing onto private property.