IMPREGNATION OF RADIATA PINE WOOD BY VACUUM TREATMENT - IDENTIFICATION OF FLOW PATHS USING FLUORESCENT DYE AND CONFOCAL MICROSCOPY

Radiata pine sapwood and heartwood were dried with or without pre-stea ming and then impregnated by vacuum treatment with water, toluidine bl ue and fluorescein. Sapwood uptake was 0.571 g/cm(3) and was not affec ted by pre-steaming. As expected, the uptake by heartwood that had not been pre-steamed was very low. Pre-steaming increased liquid uptake f rom 0.113 g/cm(3) to 0.438 g/cm(3). When the uptake by pre-steamed hea rtwood from radial, tangential and transverse surfaces was compared, t he greatest increase was from the radial surfaces, suggesting that pre -steaming of heartwood resulted in changes to the tangential liquid fl ow pathways. The liquid flow pathways in sapwood consisted of axial an d radial resin canals, ray parenchyma cells in both fusiform and unise riate rays. Penetration into tracheids was also observed. Without pre- steaming, there was limited liquid flow into heartwood, and this was g enerally confined to resin canals and ray parenchyma. Pre-steaming of heartwood increased penetration of dye into the resin canal network, p resumably due to removal or redistribution of resin. Fluorescein was a lso evident in bordered pits between tracheids, suggesting that one of the ways that pre-steaming increased heartwood treatability was by al tering the condition of bordered pits to allow greater conduction. The combination of fluorescein dye and confocal microscopy was found to b e a particularly effective way of visualising flow patterns, as it was possible to examine thick sections, which avoided microtome damage at the section surface. Examination of dry wood also minimised the possi bility of dye redistribution.