Fe-Sem Observations on the Microfibrillar Orientation in the Secondary Wall of Tracheids

Abstract

Field emission scanning electron microscopy was used to observe the inner surfaces of the developing secondary walls of earlywood tracheids of Abies sachalinensis Masters. Microfibrillar orientation in the secondary wall, as seen from the lumen side, changed in a clockwise direction from the outermost S1 to the middle of the S2 and from there counter-clockwise to the innermost S3. Sometimes microfibrils oriented in a steep S-helix were observed in the S3 layer. Lamellae showing different microfibrillar orientations in wall layers other than the S2 were observed beneath newly deposited microfibrils on the inner surface of the developing wall. Furthermore, on the inner surface of the wall forming the S12, S23 and S3, lamellae with microfibrils closely aligned at the same angle as one another and lacking spaces were not observed. These observations suggest that in layers other than the S2 most lamellae are not composed of closely spaced microfibrils.