1. Arcamone, F., Chain, E. B., Ferretti, A., Minghetti, A., Penella, P., Tonolo, A., and Vero, L., Proc. Roy. Soc., B, 155, 26 (1961).
2. Wells, D. A., and Soffe, R., J. Agric. Eng. Res., 7, 42 (1962).
3. Kobel, H., Brunner, R., and Brack, A., Experientia, 18, 140 (1962).