1. Allen’s Commercial Organic Analysis 5th ed. Vol. VII. London: Churchill 1929.
2. Henry, T.A.: The Plant Alkaloids, 4th ed. London: Churchill 1949.
3. Manske, R.H.P., and H.L. Holmes: The Alkaloids, Vol. I. New York: Academic Press Inc. 1950; Vol. II, New York: Academic Press Inc. 1952. Vol. III 1953.
4. Winterstein, E., and G. Trier: Die Alkaloide, Pt. I, 2nd ed. Berlin: Borntraeger 1928: Pt. II, 2nd ed. Berlin: Borntraeger 1931.