Ultrastructural Characteristics of Red Maple ( Acer Rubrum L.) Wood

The anatomy of red maple ( Acer rubrum L.) was examined using the transmission electron microscope. Direct carbon replicas and ultrathin sections of inner and outer sapwood and inner and outer heartwood were prepared. In cross-sectional view sapwood intervessel pit membranes appear thin; in surface views of air-dried and extracted samples of the second sapwood ring and inner sapwood, openings in the intervessel pit membranes are visible. Intervessel pit membranes are permeated with extractives in the heartwood. Vessel-ray parenchyma pits have been described as similar to intervessel pits; but differences in shape, apertures, and pit membranes were detected in this study. The ray parenchyma cells appear different in ultrastructural details from those in species that have been studied with the transmission electron microscope as they do not have well-defined protective layers in the sapwood when they are adjacent to vessels, plasmodesmata channels are not apparent in the parenchyma-parenchyma pits, and there are no pits to the intercellular spaces in the rays. Red maple is an unusual hardwood as it has longitudinal intercellular spaces adjacent to the fibers; the appearance of these spaces is similar to that of the longitudinal intercellular spaces in members of the conifer family, Araucariaceae.