Tangential Wall Thickenings in Conifer Tracheids At Ray-Contact Areas

Abstract

Measurements made on transverse and longitudinal sections of mature wood of red pine and white cedar established that the greater thickness of tangential tracheid walls at the areas where tracheids are in contact with uniseriate rays is proportional to the reduction in tangential width of tracheids at these areas and to the tangential width of the uniseriate rays. It is concluded that "ray thickenings" do not comprise an additional deposition of cell-wall material but arise from changes in the configuration of existing wall material at the ray contact areas.