1. Mitchell, E. M., Amer. J. Bot., 17, 117 (1930).
2. Winterstein, E., Z. physiol. Chem., 17, 353 (1893).
3. Krishna, S., and Ghose, T. P., Indian Forest Leaflet, Forest Research Institute, Dehra Dun, No. 23 (1942) and No. 47 (1943).
4. Savur, G. R., and Sreenivasan, A., Current Sci., 15, 43 (1946).
5. Frank, A. B., Jahrb. Wiss. Bot., 5, 161 (1866).