Ultrastructural Characteristics of Mature Wood of Southern Red Oak ( Quercus Falcata Michx.) and White Oak ( Quercus Alba L.)

The fine structure of mature wood of white oak and southern red oak was studied using ultrathin sections and direct carbon replicas. In most details, the fine structure of the wood of these two species is similar. Differences detected include a slightly coarser appearance of intertracheary pit membranes and fewer vessel-ray parenchyma pit contacts in southern red oak. Intervessel pitting was not found in either species, implying that flow between vessels occurs via vasicentric tracheids as vessel-vasi-centric tracheid and vasicentric tracheid-vasicentric tracheid pitting is abundant. The appearance of the pit membranes differs in pits interconnecting different types of cells, e.g. vessel-vasicentric tracheid pit membranes were thicker than vasicentric tracheid-vasicentric tracheid pit membranes. Differences in the orientation of the pit aperture in the bordered pits of various cell types appeared to correlate with differing S 2 orientations. Vessel-vasicentric tracheid and vasicentric tracheid-vasicentric tracheid pit membranes in the outer conducting sapwood and inner nonconducting sapwood appeared similar with randomly arranged microfibrils and no visible openings. In the outer and inner heartwood, these membranes were coated and infiltrated by extractives. The low permeability of multiseriate rays compared with uniseriate rays may be accounted for by the scarcity of lateral wall pitting and direct vessel-ray parenchyma cell contact in the interior of the multiseriate ray.