1. Mothes, K., Engelbrecht, L., and Kulaeva, L., Flora, 147, 445 (1959).
2. Parthier, B., Flora, 154, 230 (1964).
3. Richmond, A. E., and Lang, A., Science, 125, 650 (1957).
4. Kulaeva, O. N., Fiziol. Rasten., 9, 229 (1962).
5. Mullins, M. G., J. Exp. Bot., 18, No. 55, 206 (1967).