Atomic force microscopy of torus-bearing pit membranes
Atomic force microscopy was used to compare the structures of dried, torus-bearing pit membranes from four woody species, three angiosperms and one gymnosperm. Tori of Osmanthus armatus are bipartite consisting of a pustular zone overlying parallel sets of microfibrils that form a peripheral corona. Microfibrils of the corona form radial spokes as they traverse the margo. Margo microfibrils are loosely packed thus facilitating passage of water molecules. The pustular layer is removed by acidified sodium chlorite. Tori of Cercocarpus montanus also have a pustular surface, but lack a corona. Tori of Pinus taeda have a finely granular to amorphous torus matrix. Ulmus alata tori have microfibrils traversing the surface. The atomic force microscope proves itself a useful tool for high resolution study of pit membranes with only minimal specimen preparation.