1. Garnjobst, L., and Wilson, J. F., Proc. US Nat. Acad. Sci., 42, 613 (1956).
2. Rizet, G., and Esser, K., CR Acad. Sci., 237, 760 (1953).
3. Bernet, J., Ann. Sci. Nat. Bot., 4, 611 (1965).
4. Bernet, J., CR Acad. Sci., D, 265, 1330 (1967).
5. Begueret, J., and Labarere, J., Ann. Gen. (in the press).