1. Y. Z. Lai and K. V. Sarkanen, “Lignins,” ed. by K. V. Sarkanen and C. H. Ludwig, Wiley-Interscience, New York, 1971, p. 294.
2. O. P. Grushnikov and N. N. Shorygina, Russ. Chem. Rev., 39, 684 (1970).
3. T. Higuchi and I. Kawamura, Holzforsch., 20, 16 (1966).
4. T. Yamazaki and T. Higuchi, Mokuzai Gakkaishi, 17, 117(1971).
5. T. Higuchi. Y. Ito, M. Shimada and I. Kawamura, Phytochemistry, 6, 1551 (1967).