  We can propound a thermo-mechanical understanding of the ascent of sap to the
top of tall trees thanks to a comparison between experiments associated with
the cohesion-tension theory and the disjoining pressure concept for liquid
thin-films. When a segment of xylem is tight-filled with crude sap, the liquid
pressure can be negative although the pressure in embolized vessels remains
positive. Examples are given that illustrate how embolized vessels can be
refilled and why the ascent of sap is possible even in the tallest trees
avoiding the problem due to cavitation. However, the maximum height of trees is
limited by the stability domain of liquid thin-films.
