Distribution and Structure of Torus-Bearing Membranes in the Wood of Schisandra chinensis

Abstract

Torus-bearing pit membranes control water movement between tracheary elements of vascular plants, while at the same time they inhibit spread of air embolisms.  They are common in gymnosperms but relatively rare in angiosperms.  A recent manuscript noted the presence of such membranes in Schisandra chinensis, a species of basal angiosperm.  Building on this prior report, the present manuscript presents evidence for the presence of this membrane in four more species of the genus.  The torus-bearing pit membranes are best developed between tracheids, a cell type that acts as a subsidiary conducting system to the vessel members.  Detailed observations with an atomic force microscope show the torus to be deposited after formation of the subtending margo is complete.