1. Darlington, C. D., J. Genet., 31, 185 (1935).
2. Lederberg, J., J. Cell. Comp. Physiol., 45, suppl. 2, 75 (1955).
3. Freese, E., Genetics, 42, 671 (1957).
4. Belling, J., Univ. Calif. Publ. Bot., 14, 283 (1928).
5. See Whitehouse, H. L. K., The Mechanism of Heredity (Edward Arnold, London, 1965).