1. J.F. Morton, Econ. Bot.25, 457 (1971).
2. J.F. Morton, Cancer Res.28, 2268 (1968).
3. For definitions of terms see E. Hecker, Int. J. Cancer18, 122 (1976); Z. Krebsforsch.86, 219 (1976); GANN67, 471 (1976); WHO-Bull.54, 1 (1976) and Hecker4.
4. E. Hecker, Symp. Mechanisms of Tumor Promotion and Cocarcinogenesis, March 1977, Gatlinburg, Tennessee, vol. 2, p. 11, Raven Press, New York 1978.
5. R.W. O'Gara, C. Lee and J.F. Morton, J. natl. Cancer Inst.46, 1131 (1971).