1. Coulter, J. M., andChamberlain, C. J. (1912). Morphology of Angiosperms. New York.
2. Hayward, H. E. (1951). The structure of economic plants. New York.
3. Veen, R.van der, andMeijer, G. (1958). Licht und Pflanzen. Phillips’ technische Bibliothek, Eindhoven, Holland, 48–9.
4. Went, F. W. (1957). The experimental control of plant growth. Waltham, Mass., 148.