CHAPTER II 



THE HIGH MAGNIFICATION CRESCOGRAPH 



The essential difficulty in investigations on growth arises 

 from its extraordinary slowness. The average rate of longi- 

 tudinal growth in a plant is about Toihuu inch per second, 

 a length which is half that of a single wave of sodium light. 

 Even with the magnifying growth-recorders hitherto 

 employed, it takes several hours to detect and measure its 

 rate. For the accurate investigation of the effect of any 

 given agent on growth, it is necessary to keep all other 

 conditions, such as light and heat, strictly constant through- 

 out the experiment ; even if this were possible, there would 

 probably be some autonomous variation of the rate of 

 growth during such lengthy periods. Considerable un- 

 certainty is inevitable in results obtained by a method 

 which involves a long time for observation. The element 

 of uncertainty can only be eliminated by reducing the 

 period of the experiment to a few minutes, but that 

 necessitates devising a method of very high magnification 

 and an automatic record of the magnified rate of growth. 



The Optical Lever 



The problem of high magnification w^as first solved by 

 the employment of my Optical Lever, where an axis carrying 

 a mirror undergoes rotation proportional to the growth 

 elongation. The reflected spot of light magnified the 

 movement of growth from looo to 10,000 times. The 

 vertical movement of the spot of light was converted into 



