1. ZIMMERMAN, P.W. and CROCKER, W., Boyce Thompson Inst. Prof. Pap.1, 222 (1933).
2. ZIMMERMAN, P.W. and CROCKER, W., Contrib. Boyce Thompson Inst.6, 167 (1934).
3. RAO, A.V., FALLIN, E. and FANG, S.C., Plant Physiol.41, 443 (1966).
4. JOHN, M.K., Anal. Chem. (in press).
5. HATCH, W.R. and OTT, W.L., Anal. Chem.40, 2085 (1968).