1. M. Goryaev and I. Pliva, Methods of Investigating Essential Oils [in Russian], Alma-Ata (1962), p. 594.
2. P. de Mayo, The Higher Terpenoids, Interscience, New York (1959).
3. F. Šorm and L. Dolejs, Guaianolides and Germacranolides, Hermann, Paris (1965).
4. K. S. Rybalko, Natural Sesquiterpene Lactones [in Russian], Moscow (1978).
5. Handbook [in Russian], Academy of Sciences of the Uzbek SSR, Tashkent (1976), p. 110.