The Role of Intervessel Pits and Vessel Plugs in Determining Flow Pathways Through and Between Vessels in Sycamore (Acer pseudoplatanusL.)

Abstract

It has previously been suggested from physical evidence that vessels in twigs of sycamore (Acer pseudoplatanus L.) are connected by small pores in intervessel pit membranes. From results obtained using a combination of physical techniques and electron microscopy it is clear that this is an oversimplification: almost all intervessel pit membranes are absent in sycamore twig and stem wood, yet physical tests still suggest that vessels are connected by pores smaller than pit apertures. Where these pores are is less certain. They may be in plugs observed to fill vessel lumens. They may possibly be in a small number of intact intervessel pit membranes in the terminal elements of vessels, but such membranes could not be found under the microscope. In either case, the results of physical tests suggest that vessels connected by membraneless intervessel pits must effectively end together at a particular point in the tree.