1. Hughes, L. G., and Fowler, H. D., Nature, 172, 316 (1953).
2. Bird, L. S., and Joham, H. E., Plant Dis. Rept., 43, 86 (1959).
3. Knight, R. L., and Clouston, T. W., J. Genet., 38, 133 (1939).
4. Schaffer, P. A., and Hartman, A. F., J. Biol. Chem., 43, 349 (1920–21).
5. Hassan, H. M., Ph.D. thesis, University of Cambridge (1953).