Note on the mechanics of the ascent of sap in trees

The following remarks, relating to one of the most powerful and universal of the mechanical operations of organic, are based mainly on the numerous experimental results reported in Dr. A. J. Ewart’s recent memoir. Their chief object is to assert the view that we are not compelled to subject to the great actual pressure, amounting in high trees to many atmospheres, that is sometimes postulated. It is hardly necessary to remark that the problem of the rise of sap is one of mechanics, in so far as concerns the mode of the flow and the propelling power. Contrary to the view above referred to, it seems not unreasonable to consider that the weight of the sap in each vessel is sustained in the main by the walls and base of that vessel, instead of being transmitted through its osmotically porous base to the vessels beneath it, and thus accumulated as hydrostatic pressure.