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The microfibril angle of the S2 layer and the ultrastructure of the intertracheid bordered pit membrane in Japanese cedar (Cryptomeria japonica D. Don) and Taiwania (Taiwania cryptomerioides Hay.) were investigated via an improved microfibril angle measuring method and electron microscopy.
The microfibril angle can easily be measured under light microscope, when wood sections are treated with ultrasound wave and cobalt chloride solution. Pit aperture angle and tracheid length were used to reconfirm the correctness of the improved microfibril angle measuring method.
The correlations between fiber length and microfibril angle , microfibril angle and pit aperture angle were significant. The largest microfibril angle of both Japanese cedar and Taiwania occurs at near the pith and tends to decrease in the radial direction. Microfibril angle is the largest at the base of the tree and decreases with increasing height. Japanese cedar has a larger microfibril angle than Taiwania during the first ten years of growth, but a smaller fiber angle after that. It can be suggested that the Japanese cedar was growing faster than the Taiwania for the first ten years.
The pit membrane of Japanese cedar and Taiwania can be classified by the shape of the torus. In Japanese cedar, the torus is usually convex lens-shaped, fusiform shaped, or flat disk-shaped. In Taiwania the torus is usually fusiform shaped, flat disk-shaped, or linear. The pustules at the central part of the torus are a special characteristics of latewood pit membrane in Japanese cedar.
Besides the natural structure of bordered pitting, the external incrustations on the pit membrane are a noticeable point in this research. The incrustations exist on the pit membrane in both sapwood and heartwood of both trees. Image analysis software shows that heartwood has more deposition than sapwood and latewood has more deposition than earlywood.
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