Time course of the secondary deposition of incrusting materials on bordered pit membranes in Cryptomeria japonica

Bordered pit membranes of Cryptomeria japonica were examined successively from the outermost sapwood to the heartwood by scanning electron microscopy and by ultraviolet microspectrophotometry in an attempt to evaluate the time course of the secondary deposition of incrusting materials and to gain clues to their chemical composition. Scanning electron microscopy revealed that the bordered pit membranes were covered by incrusting materials from the middle layer of the sapwood to the heartwood. Both the amount and the appearance of the deposited incrusting materials differed among four regions of the wood, namely, the middle to inner layer of the sapwood, the innermost layer of the sapwood, the intermediate wood and the heartwood. From our results it appears that, in C. japonica, incrusting materials are deposited on bordered pit membranes by stages over several years. Apparent absorption of ultraviolet light by the bordered pit membranes was detected in the analysis of the innermost layer of the sapwood, the intermediate wood and the heartwood. The incrusting materials deposited in these zones were probably phenolic compounds. However, differences in the manner and extent of the absorption of ultraviolet light were found between these three regions of the wood. The results of microspectrophotometric analysis also suggested the phased deposition of incrusting materials at the bordered pit membranes of C. japonica.