BORDERED PIT ASPIRATION IN THE WOOD OF CRYPTOMERIA-JAPONICA IN RELATION TO AIR PERMEABILITY

Aspiration of bordered pits in Cryptomeria japonica (L. f.) D. Don was studied in relation to the air permeability in sapwood, transition zo ne wood, and heartwood. The percentage of aspirated pits relative to t he total number of bordered pits with observable tori was determined i n samples that were epoxy-embedded and thin sectioned. Air permeabilit y of air-dried and freeze-dried wood samples was measured following th e method described by Siau (1984). Pit membrane structure of air-dried and freeze-dried samples was investigated by scanning electron micros copy on split radial surfaces. It is proposed that pit aspiration prog resses during heartwood formation as already reported, but the pit asp iration was frequently incomplete and the percentage varied between in dividuals. The pit aspiration percentage was not obviously related to the sample's initial green moisture content or heartwood color. The re sults from permeability measurement and SEM observation on air- and fr eeze-dried samples suggest that pit aspiration occurred in sapwood sam ples (the initial moisture content of which ranged from 200 to 300%) d uring air-drying and caused a significant decrease in permeability con firming the pit aspiration mechanism proposed by Hart and Thomas (1967 ). In the heartwood, encrustation of pit membranes prevented aspiratio n during air-drying.