The Ultrastructure Of Southern Pine Bordered Pit Membranes As Revealed By Specialized Drying Techniques

The study of the mature bordered pit membrane from three species revealed that there were no major differences in ultrastructure. The pit membrane consists of an imperforated torus and a margo with considerable variation in porosity. Springwood pit membranes from the sapwood were rarely incrusted, whereas summerwood pit membranes from both the sapwood and heartwood were heavily incrusted.The use of specialized drying techniques, specifically solvent-exchange, critical-point, and freeze-drying techniques, prevented pit aspiration and permitted a detailed study of the pit membrane. Since the margo structure was not altered to any substantial degree by the different drying systems, it appears that the surface tension of the evaporating liquid is important only with regard to pit aspiration. A study of trees from several age classes showed the decrease of the number of margo microfibrils to be related to the age of the wood rather than to the time of formation. The mechanism of the deterioration process was not determined