1. Gillett, J. B., Kew Bull., 367 (1952).
2. Norris, D. O., Emp. J. Exp. Agric., 21, 247 (1956).
3. Olmsted, C. E., Bot. Gaz., 106, 46 (1944).
4. Van der Plank, J. E., Nature, 157, 503 (1946).
5. Allard, H. A., in Vernalization and Photoperiodism, edit. by Murneek, A. E., and Whyte, R. O. (Chronica Botanica Co., U.S.A., 1948).