The identification of the woods compromising a sample of pulp or a sheet of paper is attended by difficulties not present when identification is made of the wood before pulping. In the first place, the arrangement of the individual fibers has been destroyed so that the relations of wood elements to each other are no longer useable as distinguishing characteristics. In the second place, the action of chemicals and the hydration resulting from beating may partially obscure of destroy the minute cell characteristics necessary for the separation of closely related species of wood.