1. Siegel, A., and Wildman, S. G., Phytopath., 44, 277 (1954).
2. Bald, J. G., and Goodchild, D. J., Phytopath., 50, 497 (1960).
3. Bald, J. G., Nature, 188, 645 (1960).
4. Solberg, R. A., and Bald, J. G. (unpublished work).
5. Zech, H., Planta, 40, 461 (1952).