XXII.— THE BALANCf:D CRESCOGRAPH 



By 



Sir J. C. BosE. 



We shall in the succeeding series of papers denl with 

 the subject of tropism in general. Different plant organs 

 undergo curvature or bending, sometimes towards and at 

 other times away from the stimulus which induces it. 

 The problem is very intricate ; the possibility of its solu- 

 tion will depend greatly on the accurate determination of 

 the immediate and after-effects of various stimuli on the 

 responding organ. The curvature induced in the growing 

 organ is brought about by variation, often extremely slight, 

 of the rate of growth ; the result, moreover, is liable to 

 be modified by the duration and point of application of 

 stimulus. The difficulties connected with the problem can 

 only be removed by the detection and measurement of the 

 minutest variation in growth, and by securing a continuous 

 and automatic record of the entire history of the change. 



In the chapter on High Magnification Crescograph an 

 account is given of the apparatus which I have devised 

 by which the rate of growth may be magnified from ten 

 thousand to ten millions times. It is thus possible to 

 measure the imperceptible growth of plants for a period 

 shorter than a single second. The variation of normal 

 rate of growth is also found by measuring successive 

 growth records on a stationary plate at regular intervals, 

 say of ten seconds, or from the flexure in the growth-curve 

 taken on a moving plate (p. 163). 



I was next desirous of exalting the sensitiveness to a 

 still higher degree by an independent method, which would 



