414 



PLANT RESPONSE 



knowledge of the speed of the recording-drum, and the 

 balancing rate, and from an inspection of the curve itself, to 

 determine not only the periodicities, but also the absolute 

 value of the rate of variation of growth, at any given 

 moment. 



The compensating movement to which I have referred is 

 effected by means of an hydraulic device. The spot of light 



from the Optical 

 I.ever falls upon a 

 mirror attached to a 

 second lever, or to a 

 rotating wheel. The 

 arm of the lever, or 

 a thread which is 

 passed round the 

 wheel, is attached to 

 a float on the surface 

 of a cylinder of water. 

 Water is escaping 

 from this cylinder, by 

 means of a syphon 

 arrangement, at a rate 

 which can be adjusted 

 with the greatest 

 nicety. The float can 

 thus be made to de- 

 scend at any speed 

 that is desired, this 

 descent producing a 

 rotation of the second 

 lever or of the wheel. 



Fig. 167. Diagrammatic Representation of 

 Balanced Crescograph 

 r, plant attached to Optic Lever, L, with mirror, 

 M, attached to fulcrum-rod, resting on knife- 

 edges, A and a' ; l', lever attached to float, 

 F F, with second mirror, M, attached to its ful- 

 crum-rod ; B, balancing wheel adjusting difter- 

 ences of level of the two limbs of syphon, s. 



We have, then, two mirrors, of which one is rotated in one 

 direction by the growth-movement of the plant, and the 

 second in the opposite direction by the descent of the float. 

 A spot of light reflected on the two mirrors will thus remain 

 stationary when the precise balance is effected, by proper 

 regulation of the escape of water from the cylinder (fig. 167). 



