The Preparation of Stem Sections of Woody Herbarium Specimens

A procedure is described for sectioning the stems of woody herbarium specimens by the paraffin method. The specimens are cut into convenient sizes; boiled for one-half to one hour in order to exclude air and soak up the cell walls and membranes; cooled and placed in 5% NaOH for 24 hours in order to expand the collapsed cells and remove excessive coloring matter; washed in running water for a few hours; placed in hydrofluoric acid until sufficiently softened to cut easily with a razor blade; washed in running water for 24 hours to remove the acid; dehydrated and embedded in paraffin of high melting point (56-58°C.) according to the n-butyl alcohol method; sectioned with the rotary microtome and completed by the ordinary method. Soaking the paraffin blocks in water for a period of several hours to a day or more before sectioning greatly improves the cutting and reduces electrification of the paraffin ribbon. The method proves satisfactory not only for herbarium material but for seeds and specimens of old bark and wood varying in hardness from balsa to ebony. For seeds or specimens containing only xylem, the NaOH treatment should be omitted.