1. Döpp, W., Ber deut. Bot. Ges., 63, 139 (1950).
2. Näf, U., Growth, 20, 91 (1956).
3. Näf, U., Physiol. Plantarum, 11, 728 (1958).
4. Eames, A. J., “Morphology of Vascular Plants. Lower Groups” (McGraw-Hill, New York and London, 1936).
5. Döpp, W., Ber. deut. Bot. Ges., 72, 11 (1959).