1. Warington, R., J. Chem. Soc., 59, 484 (1891).
2. Frankland, P. F., and Frankland, G., Phil. Trans., B, 181, 107 (1890).
3. Winogradsky, S., Arch. Sci. biol. (St. Petersburg), 1 (1892).
4. Boullanger, E., and Massol, L., Ann. Inst. Pasteur, 17, 492 (1903).
5. Bonazzi, A., Bot. Gaz., 68, 194 (1919).