CHAPTER III 



THE BALANCED CRESCOGRAPH 



The Crescograph described in the previous chapter gives 

 records of the enhancement or depression of the rate of 

 growth induced by external change. The enhancement of 

 growth is shown by the increase of spacing between the suc- 

 cessive dots of the vertical record taken on a stationary 

 plate, or by the upward flexure of the curve inscribed on a 

 moving plate. Depression of the rate is, on the other hand, 

 indicated by the shortening of the distance between the 

 successive dots or by the downward flexure of the curve. 



Though these methods are highly sensitive, yet it 

 requires very careful inspection of the records to detect a 

 change induced in the rate of growth, when such a variation 

 is very slight. It was therefore necessary to devise a new 

 method which would instantly show, by the up or down 

 movement of an indicator, the accelerating or retarding 

 effect of an external agent. For this purpose I first em- 

 ployed the Optical Method of Balance,^ which was con- 

 sidered at that time to be very sensitive. The spot of 

 light reflected from the Optical Lever (which magnified the 

 rate of growth) was made to fall upon a second mirror to 

 which a compensating movement was imparted, so that 

 the light-spot, after double reflection, remained stationary. 

 Any change in the rate of growth — an acceleration or a 

 retardation — was detected by the movement of the hitherto 

 stationary spot of light, in one direction or the other. 



A still more perfect apparatus was next devised which 

 possesses several important advantages ; the exact balance 



^ Plant Response (1906), p. 413. 



