PHOTODISCOLORATION OF WESTERN HEMLOCK (TSUGA-HETEROPHYLLA) SAPWOOD .1. ACTUAL CONDITIONS UPON PHOTODISCOLORATION OF WOODY PARTS

The photodiscoloration phenomena of western hemlock (Tsuga heterophyll a (Raf.) Sarg., Pinaceae) wood were investigated using a chromameter. The methanol extract contained photodiscoloring constituents, and afte r the fractionation of this extract, almost all of the constituents we re separated into ethyl acetate soluble fraction. The constituents wer e distinguished by TLC and HPLC and a quantitative analytical method o f the main constituents was established by HPLC. The main constituents were indicated to be lignans based on other isolation and structural explaining works. Also, the presence of vanillic acid, catechin and va nillin as minor constituents was proven by co-TLC and HPLC with authen tic specimens. The importance of the sapwood part in the problem, espe cially its late wood, was revealed by experiments on the distribution of the constituents in tissues and individuals. The content of catechi n, which had been reported as the main photodiscoloring constituent of western hemlock, was little in all sapwood. Moreover, the composition of the main constituents differed among sapwood samples. Then, it was suggested that plural constituents mutually interacted in the early s tage of photodiscoloration. This suggestion was supported by the resul ts of colorimetric and light irradiation tests.