30 chap. iii. the balanced crescograph 



Experimental Verification of the Formula 



Experiment 8. — The reliability of the apparatus and the 

 accuracy of the working formula were tested by independent 

 measurements obtained (i) by the method of balance, and 

 (2) by direct micrometric measurement of growth of a 

 seedling of Wheat. 



Measurement bv the Balance Method : 



The constant of the apparatus = 10-45. 



The balancing angle of inclination = 23-5°. 



The time of a single revolution of spindle = 12 seconds. 



Hence absolute rate of growth in [ji per second 



^ 10-45 X tan 23-5 ° 

 12 



= 0-381 . . . . . (i) 



Direct measurement by Microscope-Micrometer . — The 

 micrometer was focused on a mark on the tip of the plant, 

 and the growth-elongation after an interval of 2 hours and 

 35 minutes (155 seconds) was found to be 3-5 mm. 



The rate of growth \l per second 



^ 3-5 X 1000 

 155 X 60 

 = 0-376 . . . . (2) 



The two results are practically the same, the difference 

 being in the third place of decimals. 



The Time-Factor 



The factor of time is a very important element in the 

 responsive growth-variation. Growth is not immediately 

 affected by an external change ; there is a delay in the 

 reaction, designated as the latent period ; this has to be 

 accurately determined, as also its modification under different 



