University of Cambridge > Talks.cam > Departmental Seminars in History and Philosophy of Science > How trees defy gravity: conceptual and historical remarks on the theory of the ascent of sap

How trees defy gravity: conceptual and historical remarks on the theory of the ascent of sap

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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 talk 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.

This talk is part of the Departmental Seminars in History and Philosophy of Science series.

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