The Wonderful MR Willughby by Tim Birkhead

Author:Tim Birkhead
Language: eng
Format: epub
Tags: Biography
Publisher: Bloomsbury Publishing

To paraphrase: by making cuts in birch trees he found that the flow of sap was least during the night (or if the day was cold); at other times the flow was greatest in the morning and especially vigorous from large branches and those nearest the roots. The sap continued to flow from cuts for almost two weeks. As the flow dried up, a phlegm-like substance appeared, which he assumed was part of the ‘wood’. Willughby says that ‘it’ tasted like sugar water, but it isn’t clear whether he is referring to ordinary sap or the phlegm-like sap just mentioned. I suspect he’s referring to ordinary sap since he then says he boiled some, as ‘Mr Evelin [John Evelyn]’ suggested. Boiling the sap collected from trees in spring has been practised by native peoples for a long time and is how maple syrup is made.

The other significant aspect of Willughby’s notes is the inclusion of three queries that Francis asked himself: whether sap was always the same colour as the wood; whether sap comes only from the bark; and ‘whether ye sap descend and circular [presumably meaning “circulate”] or evaporate by perspiration’.

William Harvey’s discovery in 1628 of the circulation of the blood – ingeniously demonstrated using tourniquets and simultaneously establishing the existence of valves in veins to prevent any backflow – raised the question of whether a similar circulation occurred in plants. Previously, it had been assumed that plants had no ‘sensitive soul’, an idea promoted by Aristotle and Theophrastus in the fourth century bc. However, the fact that the sensitive plant Mimosa pudica from tropical America, recently discovered in Willughby’s day, has leaflets that droop dramatically on being touched and reopen minutes later, suggested that it was far from insensitive. In fact, this plant, whose extraordinary and rapid movements continue to fascinate us, was the starting point for studies of plant physiology.

Understanding how Mimosa’s leaf movements occurred was one of the first tasks allotted to the newly formed Royal Society by Charles II. In response, the Society established a committee in 1665 to create a list of botanical questions for its members. Robert Hooke made the study of Mimosa his own, but the Society’s list – eventually published in January 1668 – also included queries relating to the rising of sap in trees: ‘In tapping, cutting or boring of any tree, whether the juyce, that vents at it, comes from above or below … What side of the tree affords most sap?’; ‘whether the sap comes more copiously at one time of the day or night, than another?’49

Willughby embraced the study of sap with the same enthusiasm and ingenuity as he did his other research. The questions and the methods that he – and later Ray – employed might seem naive to us now, but these were some of the first investigations into what we now call plant physiology. The original questions, and Willughby’s report with Ray in 1669, prompted others, including their relentlessly inquisitive and academically ambitious friend Martin Lister, to undertake more research on the same topic.

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