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

Transverse Shrinkage and its anisotropy in radiata pine and spruce were investigated by means of a LV-SEM (Low-Vacuum Scanning Electron Microscope), that allows observation of water-containing specimens. The shrinkage of tracheid cells from the saturated to the dry condition was determined by measuring tangential diameter of tracheid and lumen, radial diameter of tracheid and lumen, and thickness of tangential and radial walls. Four types of specimens, namely isolated earlywood, isolated latewood, earlywood including latewood, and latewood including earlywood were used in this study. The results are summarized as follow: The lumina shrank anisotropically by drying. This means that the tracheid cell walls shrank in width the same as in thickness. The shrinkage in width was greater for tangential walls than that for radial walls. The shrinkage in thickness was almost the same for tangential and radial walls in all specimens. Therefore, anisotropy in tracheids occurring during drying was brought about by the difference in shrinkage in width between tangential and radial walls. The shrinkage in the tangential direction of earlywood including latewood was greater than that of isolated earlywood. This suggests that latewood increases the shrinkage of earlywood in the tangential direction. Earlywood did not affect the shrinkage of latewood in any direction. Both isolated earlywood and isolated latewood exhibit anisotropy of transverse shrinkage.