In 1700 Wren was returned by the boroughs of Weymouth and Melcombe Regis to a somewhat stormy Parliament.
He was finishing several of the City churches by the addition of towers to some, where, as at S. Magnus, London Bridge, and S. Andrew’s, Holborn, the main parts had been previously built.
He gave a design for All Saints’ Church, Isleworth; it was, however, reckoned too costly, and nothing was done until, in 1705, Sir Orlando Gee left a legacy of 500l. towards the rebuilding of the church, when Wren’s design was partially adopted, and the work done by his faithful master-mason, Edward Strong.[223]
With all this work, Wren yet found time to write a treatise on ‘The rising of the sap in trees.’ It is a short treatise, evidently copied by a copyist, though a little indian-ink drawing at the side is probably Wren’s own. The question in dispute seems to have been whether this natural rising of the sap contradicted the newly discovered law of gravity.
‘It is wonderful,’ he says, ‘to see the rising of the sap in Trees. All will bleed more or less when they are tapped by boring a hole through the Bark, some very considerably, as Birch, which will afford as much liquor every day almost as the milke of a cow; in a Vine when a bough is cut off it will if not stopped bleed to death. Now by what mechanisme is water raised to such a height, as in Palmitos to 120 foot high? A skillfull Engineer cannot effect this without great force and a complicated engine, which Nature doth without sensible motion; it steals up as freely as the water descends: the reason of this is obscure as yett to naturalists.’
After some discussion of various theories, he proceeds to show by the help of the little drawing, ‘that the onely Vicissitudes of heat and cold in ye aire is sufficient to raise the sap to the height of the loftiest trees.’ Then follows the proof of this by mechanics refuting the notion of
‘a secret motion in nature contrary to that of the gravity, by which plants aspire upwards.
‘But though I have shown how the sap may be mechanically raised from the Root to the top of the loftiest trees, yett how it comes to be varyed according to the particular nature of the Tree by a Fermentation in the Root; how the Raine water entering the Root acquires a spirit that keeps it from freezing, but also gives it such distinguishing tastes and qualities is beyond mechanical Philosophy to describe and may require a great collection of Phenomena with a large history of plants to shew how they expand the leaves and produce the Seed and Fruit from the same Raine water so wonderfully diversified and continued since the first Creation.’