A COMPARATIVE INVESTIGATION OF THE ULTRASTRUCTURE OF STEAM EXPLODED WOOD WITH LIGHT, SCANNING AND TRANSMISSION ELECTRON-MICROSCOPY

The changes in anatomy, ultrastructure and topochemistry of aspen wood degraded by steam explosion treatment were investigated by light, sca nning and transmission electron microscopy. Light microscopy provided an overview of the general changes in wood architecture and revealed t he opposite roles of the vessels and ray cells. Scanning electron micr ographs showed the fibrillar architecture of the fibre surface. Transm ission electron micrographs showed that in addition to lignin redistri bution on both the inner and outer surfaces of the cell wall, this als o occurs inside the cell wall itself. Lamellar deposition of lignin wi thin the secondary cell wall and free fibrils in the extract were also observed. Special studies were undertaken to ensure that the best met hod was used to dry the wet samples for examination in the scanning el ectron microscope. Observation on all the three different microscopica l levels is probably the best possible approach to this ultrastructura l problem.