1. British Pharmaceutical Codex. The Pharmaceutical Press, London 1973; 122–123
2. British Pharmacopoea. Appendix IVe, A66, Appendix Villa. Her Majesty's Stationery-Office, London 1973; A84: 119
3. Carlton's Histological Technique, R. A. B. Drury, E. A. Willington, R. Cameron. Oxford University Press, New York 1967; 50–52
4. Trease G. E., Evans N. C. Pharmacognosy, 12th ed. Bailliere Tindall, London 1983; 333