Most of the collecting that goes on in the Herbarium occurs at the Washington Park Arboretum. Collecting lists are made by first determining which plants are in fruit or flower, as the most valuable specimens have one or the other. A collection list in June might include Ceanothus sp., Weigela sp. and Syringa sp. (Lilacs). Once the plants are chosen, the Arboretum master list is cross-referenced with our inventory of herbarium sheets so that we collect specimens that we don't already have.
Since a major part of the mission of the herbarium is to house voucher specimens for the WPA, specimens are collected from each individual accessioned plant. Often, we'll then narrow our collecting list to a particular area in the Arboretum. Then, we pull the maps for the sections where we will be collecting. The WPA is sectioned off into grids, and each grid has an accompanying map with specimen location information. With maps and a collecting list in hand, we head out to the field and collect.
Locating the plants is a bit like searching for treasure, but treasure isn't actually found unless the plant is in full flower or fruit - whichever state is desired for collecting purposes. In a collecting book, we record our name, the date, the name and family of the plant, a unique collecting number for each specimen, and comments about the plant and it's immediate environment, including dimensions, aspect, surrounding plants and canopy cover.
Pressing and Mounting Specimens
Once specimens have been collected, we return to the herbarium to press them. Plants are arranged so as to show as many parts as possible - flower and fruit may be cut in half to display parts, and leaves are arranged so that both sides of the leaf are displayed. Care is also taken to arrange the plant so that it will fit on standard mounting paper, which is 11" x 17". Specimens are pressed in a sandwich consisting of newspapers, absorbent felt blotter paper and cardboard ventilators. The stacks is secured at either end with wooden frames, called press ends, and then straps are wrapped around the entire stack and tightened. The goal is to have specimens as flat as possible, because shelf space in a herbarium is a hot commodity.
Specimens may be dried in a large oven at low temperature, or they may be left for several days to air dry. Labels are then made for the specimens, using the collection notes. When the specimens are dry and the labels have been made, they are ready to be mounted glued).
Herbarium specimens are mounted on acid-free paper, which ensures the longevity of the paper and prevents acids from altering the specimens. Fragment folders are mounted along with the specimen and label. Fragment folders are envelopes, and they hold plantparts that are too small to glue or extra flowers, fruits or leaves. A terrific visual tour of an herbarium specimen can be found at the New York Botanical Garden's herbarium site.