"Shihu", a famous Chinese traditional drug, is used to replenish the vital essence of the lung and stomach, to clear up the excessive heat and to promote the secretion of the body fluid. The commercial crude drugs under the general name "Shihu" are mostly derived from a number of species of the genus Dendrobium. It is difficult to identify exactly the botanical origin of these crude drugs through macroscopical examination. In order to tackle this problem, the leaf sheathes of the stems of 16 species of the genus Dendrobium are examined microscopically and the characteristics of their epidermal cells and calcium oxalate crystals are compared. The diagnostic features found are proved to be useful for the identification of the botanical origin of commercial samples of the "Shihu". In this paper the microscopical characters of 16 Dendrobium species are described with illustration.