1. Charnley, T., Perrin, R., and Porter, D., Nature, 257, 389–390 (1975).
2. Brunn, J., Beitr. Biol. Pft., 9, 307–358 (1909).
3. Ruge, U., in Catalogue Films Sclentifiques (Service du film de recherche scientifiquei Paris, 1947–1948).
4. Aimi, R., Bot. Mag., Tokyo, 76, 374–380 (1963).
5. Fondeville, J. C., thesis. Univ. Poitiers (1964).