Pits of a softwood (Pinus wallichiana) and a hardwood (Mallotus japonicus) were studied by Cryo-scanning electron microscopy (Cryo-SEM). The samples were chemically untreated and fully hydrated during freezing. Tori of P. wallichiana were frequently aspirated. It is not clear whether torus aspiration was caused by the freezing process or other factors during preparation. Aspirated tori had a turgid appearance. Offcenter aspirated tori which did not completely cover the pit pore could be detected. The margo strands were usually quite large and fanned out into fibrillar structures at the pit border. Pit membranes of M. japonicus had a very granular appearance. No fibrillar structures, different layers or pores could be detected. The granular structures may have developed from a continuous layer covering the pit membrane during freezing. Cryo-SEM is discussed as a further suitable tool for obtaining novel information about the native state of pit membranes. Future studies are needed to validate whether all observed features represent characteristics of the native state.
Seasonal changes in the distribution of water in the outer growth rings of Fraxinus mandshurica var.japonica were visualised by cryo-scanning electron microscopy using samples in which water was freeze-fixed in the living trunk . During the growing season from mid-May to late-July when formation ofxylem progressed steadily, all cell lumina of the newly forming xylem elements were filled with water. From August to October, water was lost from the lumina of wood fibres in the current-year xylem. Loss of water from wood fibres began in August at the initial zone of the earlywood, and progressed toward the cambial zone. By November, water had disappeared from the lumina of current-year earlywood vessels, and water reappeared in the lumina of earlywood fibres around the currentyear earlywood vessels. Our results indicate that cavitation in lumina of current-year earlywood vessels occurred during the period from October to November.
Water conduction and wood anatomy of Salix sachalinensis attacked by watermark disease were investigated. The internal symptom, the watermark, appeared as a brown to brown-black stained zone in sapwood. Dye injection tests revealed that water conduction did not take place in the watermark. However, soft X-ray photography and cryo-scanning electron microscopy revealed that the watermark had a high moisture level. In the watermark, some of the vessels were plugged with tyloses and masses of bacteria, and some of the ray parenchyma cells caused necrosis. Hence, the non-conductive watermark in sapwood can be considered similar to discoloured wood or wetwood.
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