連続木口切片による広葉樹繊維形態の立体的解析

Abstract

数種の広葉樹材の連続木口切片を作製し, ディジタイザとパーソナルコンピュータを用いて木部繊維の横断面のフェレ径, 周囲長, 面積, 壁厚を測定し, その軸方向の変化を追跡した。さらに軸方向柔細胞との対比により, 伸長成長による繊維の形の変化について検討した。木部繊維断面のフェレ径では, 概して接線フェレ径よりも放射フェレ径の方が大きかった。フェレ径の軸方向変化では, 放射フェレ径が比較的一定の値を示す領域 (body 部) が繊維中央でしばしば認められた。壁厚のばらつきは大きいが, 接線壁と放射壁ではほぼ等しいかあるいは前者が大きい傾向がみられた。同一放射列上の軸方向柔細胞と繊維の横断面寸法を比較した結果, 伸長成長の著しい繊維では断面形状の変化に伴ってフェレ径は変化するが, 周囲長には大きな変化は認められなかった。環孔材孔圏や散孔材の年輪はじめの繊維では伸長成長は少ないが, フェレ径, 周囲長はともに増大する傾向がみられた。

Hardwood fibers change their shapes and dimensions with their elongation growth during differentiation. For stereo-analysis of the fiber form in hardwood, cross-sectional dimensions of fibers were measured in serial transverse sections, using a digitizer (Gradimaster U4-30mark II) attached to a personal computer (EPSON PC-286V). The outline of each fiber cross-section was traced by a graphic pen on a micrograph placed on the digitizer. Feret's diameters and perimeters of fiber cross-sections were measured in each micrograph in a series, and the change of the dimensions along fiber length was compared with that along a strand of axial parenchyma cells which belong to the same radial file of the fibers examined. In the change of radial Feret's diameter of fibers there was a distinctive feature that the diameter increased from the tip to the central part of fiber (fiber body), and it was almost constant throughout the part. Wall thickness showed considerable variation along fiber length, but tangential wall thickness was slightly larger than or almost the same with radial wall thickness. Cross-sectional dimensions of the fiber were changed by intrusion of elongating fiber tips into radial files. In shioji (Fraxinus spaethiana), the radial Feret's diameter of the late wood fiber (largely elongated) was larger than that of the axial parenchyma cell, but the tangential Feret's diameter of the former was smaller than of the latter. Since perimeters of the two were nearly equal to each other, cell expansion in radial direction didn't occur in the late wood fiber, but the fiber was transformed radially by intrusive tips of other fibers located in the upper or lower position. On the other hand, in the early wood fiber (less elongated) of shioji the perimeter and radial Feret's diameter were larger than those of the axial parenchyma cell. It indicates that the fiber actually expanded in radial direction.