1. Meyer, D. R., and Anderson, A. J., Nature, 183, 61 (1959).
2. Saubert, S., and van Gijlswijk, N. O., S. Afr. J. Sci., 53, 233 (1957).
3. Annual Report of the Plant Phys. Res. Inst., University of Pretoria, 1958.
4. Annual Report of the Plant Phys. Res. Inst., University of Pretoria, 1955–1956.
5. Annual Report of the Plant Phys. Res. Inst., University of Pretoria, 1957.