of growth in developing shoots and growing leaves by marking them and measuring the distance between the marks after an interval of time. He describes (p. 330) and figures (p. 344) with his usual thoroughness the apparatus employed: this was a comb-like object, shown in Plate IX, made by fixing five pins into a handle, 1⁄4 inch apart from one another: the points being dipped in red-lead and oil, a young vine-shoot was marked with ten dots 1⁄4 inch apart. In the autumn he examined his specimen and finds that the youngest internode or "joynt" had grown most, and the basal part having been "almost hardened" when he marked, had "extended very little." In this—a tentative experiment—he made the mistake of not re-measuring his plants at short intervals of time, but it was an admirable beginning and the direct ancestor of Sachs'[1] great research on the subject.
In his discussion on growth it is interesting to find the idea of turgescence supplying the motive force for extension. This conception he takes from Borelli[2].
Hales sees in the nodes of plants "plinths or abutments for the dilating pith to exert its force on" (p. 335); but he acutely foresees a modern objection[3] to the explanation of growth as regulated solely by the hydrostatic pressure in the cell. Hales says (p. 335): "but a dilating spongy substance, by equally expanding itself every way, would not produce an oblong shoot, but rather a globose one."
It is not my place to speak of Hales' work in animal physiology, nor of those researches bearing on the welfare of the human race which occupied his later years. Thus he wrote against the habit of drinking spirits, and made experiments on ventilation by which he benefited both English and French prisons, and even the House of Commons; then too he was occupied in attempts to improve the method of distilling potable water at sea, and of preserving meat and biscuit on long voyages[4].
We are concerned with him simply as a vegetable physiologist
