The Ultrastructure of Differentiating and Mature Bordered Pit Membranes From Cypress (Taxodium Distichum L. Rich.)

The bordered pit membrane of cypress is characterized by a margo and torus composed of a dense network of microfibrils oriented in a predominately radial direction with amorphous materials deposited on the torus. Incomplete border pit aspiration often results, presumably because of the angular shape of the inner side of the pit aperture and the fact that the torus is only slightly larger than the aperture. Differentiating pit membranes are characterized by a decidedly thickened torus formed prior to secondary border formation. Removal of the matrix substance from the margo and thinning of the torus occur simultaneously. After matrix removal, the margo is perforated and the torus attains its mature dimension