1. Handley, W. R. C. (1956). Aspects of the significance of polyphenols in soil organic matter. Chem. and Ind., Nov. 10, 1956, p. 1301 (Abstract).
2. Hinton, J.C.(1932). Studies on maturity of fruit. I. Introductory. II. Preliminary observations on the rate of softening of apples. Ann. Rep. Long Ashton Res. Sta. 1931, 40.
3. Kertesz, Z. 7.(1951). Thepectic substances (628 pp.). Interscience Publishers, New York and London.
4. Kieser, M. E., Pollard A., andStone, A. M. (1950). The clarification of apple juice. II. The estimation of pectic enzyme activity. Ann. Rep. Long Ashton Res. Sta., 1949, 153.
5. Murneek, A. E. (1921). A new test for maturity of the pear. Oregon agric. exp. Sta. Bull. no. 186, pp. 8–10.