The Ultrastructure of Pits in Paulownia Tomentosa

The pitting between various cell elements in Paulownia tomentosa was studied at the ultrastructural level. Plasmodesmata are more numerous in the pit membranes of ray parenchyma than in the longitudinal parenchyma. The edges of the pit borders in the latter are curved, while those of the former are more angular in shape. Numerous blind pits were found in ray parenchyma cells, but they occurred less frequently in fiber tracheids. The tylosis wall with a "compound middle lamella equivalent" layer archs over the half-bordered pit pair area, sometimes showing a recess at the half-bordered pit pair area. The pit membrane of all pitting types is a continuation of the compound middle lamella. Pit borders of vessel pits show a variety of forms and shapes. In bordered pit pairs, the S1 of the pit border ends at the rim of the pit chamber