1. G. A. Swan, An Introduction to the Alkaloids. New York: Wiley. 1967.
2. A. Stoll and E. J. Jucker, Alkaloide. Berlin: Urban & Schwarzenberg. 1952.
3. T. A. Henry, The Plant Alkaloids. Philadelphia: Blakiston. 1949.
4. R. H. F. Manske and H. L. Holmes, The Alkaloids. Vol. 1. New York: Academic Press. 1950.
5. R. Willstätter and E. Berner, Ber. dtsch. chem. Ges.56, 1079 (1923).