Newton Figured Out How Tree Sap Rises
When I was in college, I worried about exams and how I was getting home from the pub. When Isaac Newton was an undergrad, he came up with a theory of how water moves through plants—200 years before botanists figured it out for themselves. That’s according to an article in the journal Nature by David Beerling of the University of Sheffield’s Department of Animal and Plant Sciences. [David J. Beerling, Newton and the ascent of water in plants]
Beerling writes that between 1661 and 1665, Newton, while at Cambridge University, kept a notebook in which he jotted down musings on various matters. Buried between sections on “Philosophy” and “Attraction Electricall & Filtration” is a half page on the subject of “Vegetables.” There, the young polymath tackled the topic of plant sap, and how it might rise from the roots to the leaves.
Newton suggested that what he called a “globule” of light shining on a leaf could knock away a particle of water, causing the “juices” of the plant to “riseth” upward.
He’s loosely describing what we now refer to as the process of transpiration, in which the energy of sunlight causes water to evaporate from a plant’s surface, thereby drawing water up through the stem. These prescient ponderings are lovingly presented in the journal Nature.
Where Sir Isaac came up with this idea we’ll never know. But it suggests that before he saw that the apple must come down he was doing some serious thinking about, within the tree, what goes up.