Field Techniques Used by Missouri Botanical Garden
PRESERVING PLANTS BEFORE DRYING
Most plants will deteriorate after two or three days if they are not dried or preserved in some fashion. If they are refrigerated, they can be kept a day or two longer.
A 15 to 20 cm tall bundle of plants in newspapers can be preserved with about one liter of 50% solution of isopropanol or ethanol and water. Some collectors prefer higher concentration of 60 - 70% alcohol. If the plastic bags do not have holes, the specimens may be stored this way for several months. Holes or opening the bag may reintroduce mold spores and allow evaporation of the alcohol. Any loss in concentration of alcohol may result in mold. Lower concentration of alcohol may be used for shorter storage time, but the percentages have not been worked out. (Steven Tillett, Univ. Central de Venezuela, pers. comm.).
A 30% formaldehyde solution can also be used to preserve specimens before drying. At least 1.5 liters of solution are needed to preserve a 15 to 20 cm bundle of plants. A formaldehyde solution is much poorer at penetrating a bundle of plants than an alcohol solution; however, plants preserved in formalin seem to have insect resistance after drying. Formalin is highly toxic. Avoid any direct contact of the skin with the solution and always work in a well-ventilated area and avoid the fumes. Formalin should be the solution of last resort. Always follow label directions.
After the preserving solution is added to the bag of plants, the bag should be turned several times to evenly distribute the alcohol or formaldehyde. It is best to store bags flat, and then to turn them the next day and again the following day. This insures the alcohol or formaldehyde will thoroughly penetrate the bundle.
When pressing specimens to be preserved in alcohol or formaldehyde, number the newspapers with a black china marker or other marker which is not soluble in the preserving solution. Test all markers (including other colors of china markers) with your alcohol or formaldehyde solution. Over time inks from many markers and pens will disperse into the paper, effectively erasing any data or numbers. Pencil can also be used but it may be difficult to read. Ball point pens are not at all permanent. Some inks that do not bleed at low preservative concentration will do so at high concentration. Labels stored with plants preserved in chemicals may eventually have to be replaced, as the ink often blurs.
In drying plants preserved in alcohol or formaldehyde straighten any creases or folds in the newspaper. Otherwise it will be more difficult to open them once they are dried.
Once after collecting for several days, a shipment of additional alcohol failed to arrive. Additional plants were preserved for four days by combining 1/2 of the already fully alcoholed bundles with 1/2 bundles of fresh plants. The bundles were placed so that the moist plants were above the fresh ones. Alcohol was added when it arrived and no plants or collecting time was lost.