/ 



138 STEPHEN HALES 



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 made by fixing into a handle five pins 

 J inch apart from one another ; the points being 

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

 marked with ten dots | 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 it, 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 '^ great research on the 

 subject. In his discussion on growth it is inter- 

 esting to find the idea of turgescence supplying 

 the motive force for extension. This conception 

 he takes from Borelli.^ 



Hales sees in the nodes of plants "pUnths or 

 abutments for the dilating pith to exert its force 

 on" (p. 335) ; but he acutely foresees a modern 

 objection^ to the explanation of growth as regulated 

 solely by the hydrostatic pressure in the cell. Hales 

 says (p. 33S) : "But a dilating spongy substance, by 

 equally expanding itself every way, would not 



^ Arbeiten, i. 



* Borelli, De Motu Animalium, Pt. ii. Ch. xiii. According to 

 Sachs, Ges. d. Botanik, p. 582. Mariotte (1679) had suggested the 

 same idea. 



' Nageli, Stdrkekdrner , p. 279. 



I 



