Conducting Units: Tracheids and Vessels

Abstract

The development of upright land plants depended upon the development of a water-conducting system. In the beginning, water conduction and mechanical support were closely linked, in fact this still is the case in many present-day plants that have no vessels, like the conifers. Both water conduction and rigidity depend largely upon cell-wall lignification, and it is thought that it was the evolution of the biochemical synthesis of lignin that made upright land plants possible (Barghoorn 1964).