Observations by LV-SEM of shrinkage and anisotropy of tracheid cells with desorption

Transverse shrinkage and its anisotropy in radiata pine and spruce were inv estigated by means of a LV-SEM (Low-Vacuum Scanning Electron Microscope), t hat allows observation of water-containing specimens. The shrinkage of trac heid cells from the saturated to the dry condition was. determined by measu ring tangential diameter of tracheid and lumen, radial diameter of tracheid and lumen, and thickness of tangential and radial walls. Four types of spe cimens, namely isolated earlywood, isolated latewood, earlywood including l atewood, and latewood including earlywood were used in this study. The resu lts are summarized as follow: The lumina shrank anisotropically by drying. This means that the tracheid cell walls shrank in width the same as in thic kness. The shrinkage in width was greater for tangential walls than that fo r radial walls. The shrinkage in thickness was almost the same for tangenti al and radial walls in all specimens. Therefore, anisotropy in tracheids oc curring during drying was brought about by the difference in shrinkage in w idth between tangential and radial walls. The shrinkage in the tangential d irection of earlywood including latewood was greater than that of isolated earlywood. This suggests that latewood increases the shrinkage of earlywood in the tangential direction. Early-wood did not affect the shrinkage of la tewood in any direction. Both isolated earlywood and isolated latewood exhi bit anisotropy of transverse shrinkage.