How Does Water Ascend in Tall Trees and Other Vascular Plants?

Since the Cohesion Theory was first introduced, a series of incompatible observations has appeared in the literature. Direct measurements of xylem pressure in single vessels of higher plants and tall trees by means of the xylem pressure probe technique indicate that xylem tension in the leaves of intact, transpiring plants is often much smaller than that predicted for transpiration-driven water ascent through continuous water columns. We conclude that the available evidence warrants a critical reappraisal of tension-driven water transport as the exclusive mechanism of long-distance water transport in plants.Copyright 1995, 1999 Academic Press