82 STEPHEN HALES 



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, J inch apart from one another : the points being 

 dipped in red-lead and oil, a young vine-shoot was marked with 

 ten dots i 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 ex- 

 periment 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 physio- 

 logy, 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 



1 Arbeiten, I. 



2 Borelli, De Motu Animalium, Pt n. Ch. xiii. According to Sachs, Ges. d. 

 Botanik, p. 58-2, Mariotte (1679) ^ a< ^ suggested the same idea. 



3 Nageli, Stdrkekorner^ p. 279. 



4 See his Philosophical Experiments, 1739. 



