Failure and “Senescence” of Xylem Function

Abstract

In his review of xylem conduction, Huber (1956) wrote: “we are virtually certain that the pressures of the moving water columns in the xylem are negative most of the time, but we are equally certain that such negative pressures cannot be maintained forever. Sooner or later water columns will break. Tracheary elements are thus filled with gas, probably irreversibly. This loss of water from the conducting channels is the beginning of a chain of events which we call heartwood formation” (free translation from the German).