Physics in Perspective

, Volume 15, Issue 3, pp 320-358

First online:

The Theory of the Rise of Sap in Trees: Some Historical and Conceptual Remarks

  • Harvey R. BrownAffiliated withFaculty of Philosophy, University of Oxford Email author 

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The ability of trees to suck water from roots to leaves, sometimes to heights of over a hundred meters, is remarkable given the absence of any mechanical pump. In this study I deal with a number of issues, of both a historical and conceptual nature, in the orthodox Cohesion-Tension (CT) theory of the ascent of sap in trees. The theory relies chiefly on the exceptional cohesive and adhesive properties of water, the structural properties of trees, and the role of evaporation (“transpiration”) from leaves. But it is not the whole story. Plant scientists have been aware since the inception of the theory in the late 19th century that further processes are at work in order to “prime” the trees, the main such process – growth itself – being so obvious to them that it is often omitted from the story. Other factors depend largely on the type of tree, and are not always fully understood. For physicists, in particular, it may be helpful to see the fuller picture, which is what I attempt to provide in nontechnical terms.


Eugen Askenasy Josef Böhm Edwin B. Copeland Pierre Cruiziat Francis Darwin Henry H. Dixon George Francis FitzGerald Stephen Hales Taco Hajo van den Honert John Joly John A. Milburn Park S. Nobel J.J. Oertli William F. Picard John S. Sperry Ernst Steudle Eduard Strasburger Melvin T. Tyree Martin H. Zimmermann cohesion-tension theory rise of sap transpiration capillarity cavitation negative xylem pressure hydraulic architecture global warming climate change history of biophysics