National Tree Week: Willughby and Ray's Experiment into the Motion of Sap in Trees

Francis Willughby and John Ray undertook an experiment at Middleton Hall to discover how sap moved in trees. The results of this experiment were presented to the Royal Society in 1669. It is considered a revolutionary experiment because it was one of the earliest experiments ever undertaken to specifically investigate an aspect of plant physiology. Moreover, the result of their experiment spurred many others to also investigate aspects within this field.

The idea to undertake an investigation on the movement of sap in trees was stimulated by the discovery of how blood circulated in the human body and a newly discovered species of plant in the Americas that responded to touch. Willughby wondered whether plants were more similar to humans than had been assumed and thus whether similar processes existed in humans and plants.

Willughby had begun the experiment by himself in 1665, which was before Ray had returned from the European Tour as they had returned via different routes. In this first experiment Willughby used only birch trees but in the later experiments with Ray, they also used walnut, willow and sycamore. The use of sycamore is of note because there is an old sycamore tree, which is about 350 years old, near the Large Walled Garden at Middleton Hall. By coincidence, this dates that tree to about the time that this experiment was undertaken.

Old sycamore near the Large Walled Garden at Middleton Hall, 2015. Photograph taken by Debbie Jordan.

In Philosophical Transactions, the journal of the Royal Society, Willughby and Ray’s complete methodology, results and conclusions were published in a number of articles. They discovered that: at night and when it was cold very little sap drained; the flow of sap was greatest from the largest branches and those closest to the roots; and the sap continued to run from the cuts for nearly two weeks. Willughby also mentioned that he boiled the gathered sap with sugar in order to make syrups from it. This is the traditional method of making tree syrups and is still a method used today.

Further Reading: Tim Birkhead, The Wonderful Mr Willughby, 2018.

Francis Willughby & John Ray, "Experiments concerning the motion of the sap in trees, made this spring by Mr. Willugby, and Mr. Wray, Fellowes of the R. Society: and communicated to the publisher of the inquiries touching that subject in Numb. 40", Philosophical Transactions of the Royal Society, (1669) 4 (48): 963–965. https://doi.org/10.1098/rstl.1669.0019

Author - Debbie Jordan, Middleton Hall Volunteer.

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