A temporary water mount was prepared by mixing the dry powder with water and waiting until the material was fully hydrated.

SRM3258 is a very fine powder of a pale tan or buff color. It consists of a mixture of different-sized particles of two major types. Larger particles are multicellular, tan to pale brown, mostly 0.1-0.45 mm long or broad; details of individual cells are not visible, but cells may appear irregularly rounded. Some of these pieces have a flattened surface, sometimes with an irregularly pebbled appearance; those pieces are often of somewhat angular appearance, with a thinned edge, and occasionally incorporate a thickened, more opaque band of tissue. Small irregularly shaped particles, primarily fragments of individual cells, are not generally identifiable to cell type; these are often somewhat angular but not sharply so, usually 0.01-0.07 mm in diameter, translucent and nearly colorless to light tan. Fragments of hollow, water-conducting xylem vessels are present, sometimes in clusters of several vessels grouped together; these cell fragments are cylindrical, up to 15 µm in diameter, with pronounced helical thickenings, and colorless or nearly so. There are a large number of small, irregularly rounded particles ca. 2-9 µm long, which are translucent and nearly colorless; there are also rare more or less rounded structures that are larger (to ca. 27 µm diameter) and distinctly yellowish in color. Rare linear to narrowly rectangular fragments, sometimes with tapered ends, may be observed; these are usually ca. 8-16 µm long.

*National Institute of Standards and Technology Standard Reference Material 3258.