Abstract
Pit membrane ontogeny in radial walls of Ginkgo biloba tracheids was followed using transmission electron microscopy. Torus initiation occurs prior to initiation of the pit border and without benefit of a microtubule plexus. The developing pit membrane is associated with masses of wall material located within plasmalemma invaginations. Wall material is added in such a manner as to form a torus with highly irregular surfaces. Margo and torus are traversed by plasmodesmata, whose channels are connected by extcnsive median cavities. Matrix material is removed from both margo and torus shortly after hydrolysis of the adjacent cytoplasms. Matrix removal begins at the pit membrane surface and is not preferentially associated with the plasmodesmata. Tori in aspirated pit membranes have compacted fibrils, and their fibrillar compaction might reduce permeability to air embolisms.
Published Version
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