The morphology of normal and abnormal trabeculae were observed in the secondary xylem of Abies sachalinensis using scanning electron microscopy. Both the usual types of trabeculae and the various abnormalities observed are described and illustrated.
Axial parenchyma cells with vestures were found in the secondary xylem of Lasianthus japonicus Miq. (Rubiaceae). The vestures were always associated with reticulate thickenings. Their morphology is illustrated by SEM micrographs.
Septate wood fibres with vestures were found in the secondary xylem of Damnacanthus indicus Gaertn. fil. (Rubiaceae). The vestures were always associated with newly deposited thickenings. Their morphology is illustrated by SEM micrographs.
The free water in the vessellumina in sapwood and heartwood of Ulmus davidiana var. japonica was visualised using a cryoSEM technique, and related to the occurrence and morphology of tyloses. In the sapwood, ice crystals were present in a few latewood vesse1s but no tyloses were found. In the intermediate wood, ice crystals only occurred in some latewood vessels and many of the tyloses appeared to be collapsed in both earlywood and latewood vessels. In the heartwood, tyloses embedded within ice crystals were often observed. These observations suggest that in this species tyloses are not an obstacle to the accumulation of sap in heartwood vessels of living trees.
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.
The orientation of the microfibri1s deposited on the innermost surfaces of the tracheid wall was observed in three conifer species, Larix leptolepis, Picea jezoensis, and Picea abies, using field emission scanning electron microscopy (FE-SEM). The microfibrillar orientation is different in each tracheid and exhibits either an S- or a Z-helix. The latest microfibrils deposited were normally joined into small bundles having various widths and had a different orientation from the microfibrils beneath them. When the latest deposited microfibrils on the innermost surface were oriented in an S-helix, the microfibrils beneath them were oriented in either a flatter S-helix or in a Z-helix, and when they were oriented in a Z-helix, the microfibrils beneath them were oriented in a steeper Z-helix. This is because, as seen from the lumen side, the microfibrillar orientation changes counterclockwise from the outer S23 to the innermost S3. These microfibrillar orientations varied throughout a single annual ring in each of the three species. The commonly observed angles of these microfibril were: Larix leptolepis: 70-80°, Picea jezoensis: 60-70°, and Picea abies: 40-50° in an S-helix, and the maximum range of angles was limited in extent to about 90 degrees in all species.
The occurrence and morphology of natural tyloses and gums in the vessels of 50 Japanese hardwoods (15 ring-, 34 diffuseand 1 radial-porous woods) were investigated using SEM. Tyloses were present exclusively or predominantly in 23 species (12 ring-, 10 diffuse- and 1 radial-porous woods) and gums in 15 species (3 ring- and 12 diffuse-porous woods). In the pore zones of most of the ringporous woods both tyloses and gums first occurred in an earlier ring number from the bark than in the diffNse- and radial-porous woods. Tyloses and gums originated from both ray and axial parenchyma cells in most species which have pit pairs connecting these cells to the vessels. Except for four species, the maximum and minimum diameters of the inner pit aperture from vessels to parenchyma cells were greater than 5 and 2 µm, respectively, in those species with tyloses, whereas the diameters were less than these values in species having gums. The forms of tylosis blockings in heartwood vessels were closely related to parenchyma patterns.
A quantitative scanning electron microscopic (SEM) study of the changes in microtubule orientations and arrays during secondary wall formation has been done on conifer (Abies sachalinensis Masters) tracheids. Microtubules have similar orientations as the microfibrils being deposited in the various wall layers. The density of microtubules is different in different stages of secondary cell wall formation. Microtubules are more closely arrayed in the tracheids forming the S2 than the S12 and S3. During S3 formation, sometimes 2-7 microtubules are closely arrayed, and form bundles about 80-350 nm wide. Bundles of microfibrils of similar width were also observed during S3 formation.
An examination was made of the fine structure of bordered pit membranes in the radial walls between tracheids in the outer sapwood of Abies sachalinensis to improve our understanding of the so-called extended torus, the minute holes in the torus and the imperforate zone near the periphery of the pit membranes, Field-emission scanning electron microscopy revealed that a so-called extended torus was present in many bordered pit membranes. We examined the frequency occurrence of and variations in the extended torus within a single annual ring. The frequency tended to increase from the earlywood to the latewood within a single annual ring. In the tori of many bordered pit membranes, we detected minute holes, and the number and location of such minute holes in a single torus varied among individual pit membranes. The appearance of each minute hole also varied. An imperforate zone was observed near the periphery of the pit membrane. In this imperforate zone, we found amorphous materials, and fine fibrils were visible that were an extension of the fibrillar meshwork of the margo.