1. Pirson, A., Z. Bot., 31, 193 (1937).
2. Pirson, A., Tichy, C., and Wilhelmi, G., Planta, 40, 199 (1952).
3. Arnon, D. I., Allen, M. B., and Whatley, F. R., VIIIth Congr. Int. Bot., Paris, 1954; Rapp. et Comm. Sect., 11, 1.
4. Bergmann, L., Doctoral Thesis, 1955 (Univ. of Marburg); Flora (in the press).
5. cf. Kandler, O., Z. Naturforsch., 9b, 625 (1954); 10b, 38 (1955).