Torus Presence and Distribution in Leaves of Osmanthus Armatus

Abstract

Osmanthus armatus Diels is a member of the Oleaceae whose woody branches were previously found to possess torus-bearing pit membranes. Observations of the perennial leaves indicate that torus-bearing, pitted tracheary elements extend throughout the vasculature of the organ including the veins delimiting the areoles and the vein termini. Torusbearing tracheary elements differentiate into the vein termini but do not develop at the very ends. Rather, the distal ends of vein termini consist of tracheids without tori and of phloem containing intermediary cells. The latter cell type is a component of the phloem in the small diameter leaf veins. Tori are considered to be xeromorphic features which, along with a thick cuticle and sclereids, are advantageous for the perennial growth habit of the leaves.