Herbaria are usually described as collections of preserved plant material, rather than just as stacks of pressed plants because most herbaria house boxes for bulky items like pine cones, material such as orchid flowers preserved in alcohol, and maybe plant morphology slides, boxes of seeds, wood samples, and seaweed albums. What I find interesting in visiting collections is that curators usually have such items they want to display, ones that may never be digitized or get into online catalogues but are nonetheless fascinating. Sometimes items like albums are preserved in botanical libraries. It seems to me that if these establishments are in the same institutions as herbaria, the libraries tend to receive treasures that have value, but are either not likely to be used by a plant taxonomist or are in some way so different in makeup from what is ordinarily the purview of herbarium curators or managers that the library is considered a better place for them. The assumption, which is usually based in fact, is that a librarian will know how to take care of it, or will dig around until they find out how to take care of it. Librarians know how to find answers.
That may be why a collection of 288 blocks of polyester resin, each embedded with dried plant specimens resides in the Arnold Arboretum Horticultural Library. These were made in the 1970s at the behest of Gordon P. DeWolf, Jr., a taxonomist at the arboretum. He envisioned such a collection as ideal for educational purposes. Herbarium sheets are too fragile to be passed around among a group of students, but similar specimens embedded in resin are tough. However, making them requires a great deal of work. DeWolf convinced an arboretum volunteer, Sheila Magullion, to take on the project, and it’s her work that is now found in the library. She wrote an article on her experience in creating this collection for the arboretum’s journal, Arnoldia (Magullion, 1975). This was after she had several years experience and could confidently describe what did and didn’t work.
Right on the first page, Magullion mentions the “insidious” odor of the syrupy resin. So the work area had to be away from food, a kitchen would not do, and it had to be where the molds could be left for several days to harden undisturbed. Also, it was best that the work surface not be made of anything too precious: drops of resin were difficult if not impossible to remove completely. I picture the best venue as an airy garage with an old kitchen table on its way to the dump. What is amazing is that Magullion was not deterred by these problems and many others she encountered. It is obvious that there was a great deal of trial and error involved. And even if, like me, you have no intention of ever attempting such a project—and I am sure there are easier and safer ways to do something similar today—this article is a great lesson in observation of plant material and how it behaves during drying, being soaked in resin, and hardening.
Magullion warns that the plant material has to be totally dried and the specimens should be as good as possible since imperfections appear magnified through the resin. Also, care must be taken in the use of the catalyst that cures the resin. The process is exothermic, and if there is too much heat released too quickly, the plant tissue can bleach and the cast crack. But add too little catalyst and the resin could become cloudy. There are also clear instructions on using tweezers to place the plant material on the base coat of resin, and also on sanding and polishing the finished product. Some blocks have a card attached to the base that gives the name of the plant and the parts included. These can be read through the resin and give the specimens a herbarium-sheet look (see image above).
I mentioned in the first post in this series that there is no perfect way to represent a plant, and these blocks demonstrate this. The specimens are well protected, and floating in space gives them an oddly pleasing quality. Obviously, this technique hardly became a herbarium staple, but along with the 19th-century educational posters (Van der Schueren, 2011) and plant models that grace many herbaria and botanical libraries, they are worth preserving for their beauty as well as for what they say about the culture of a particular time when a craft in favor in the larger culture seeps into the world of plants.
After her article on embedding, Magullion (1977) wrote another one on treating material from trees and shrubs with glycerin to preserve them without pressing. The purpose here was primarily to create decorative arrangements that would be long lasting. The cuttings were sprayed with glycerin, not dipped in it. Again, through trial and error Magullion figured out what would work and what wouldn’t, so the bulk of the article is a list of plant families and what works best for each. As she mentions: “Some families refuse to absorb the glycerin mixture; some absorb it, but with poor results; and some are outstanding in their response” (p. 289). She also found that timing was important. For the smoke bush, Cotinus, “large plumy fruit panicles last very well if collected no later than July.” For the birch family, foliage didn’t respond well if collected early in the year, but could be preserved if picked in August and September. Again, I won’t be doing any of this, but it is interesting to read through the families and see what Magullion discovered.
References
Magullion, S. (1975). Botanical embedding. Arnoldia, 36(6), 265–275.
Magullion, S. (1977). A guide by plant family to foliage preservation. Arnoldia, 37(6), 289–304.
Van der Schueren, K. (2011). The Art of Instruction: Vintage Educational Charts from the 19th and 20th Centuries. San Francisco: Chronicle.
Herbarium World 