THE BALANCED CRESCOGRAPH 261 



at a medium speed, the bell striking 35 times in a minute. 

 A microscope micrometer is focussed on a mark made on 

 the plant-holder, and the amount of subsidence of the 

 mark determined after one minute ; this was found to be 

 0'0525 mm. As this fall occurred after 35 strokes of the 

 bell the subsidence per stroke was 0*0015 mm. 



Determination of the absolute rate of growth. — If growth 

 be found balanced at N strokes of bell per minute, the 

 rate of subsidence per second = N x -^— mm. per second 



= N X '000025 mm. per second 



= N X "025 fi per second 



= M X 10~'' inch per second. 



Example. — The growth of a specimen of Zea Mays was 

 found balanced when the number of strokes of the bell 

 was 20 times in a minute. 



Absolute rate of growth = 20 x '025 fi = 0*5 /x per second 

 or = 20 X 10-3 inch 



or = ' 



^ 50,000 " '» 



If we take the wave length of sodium light X as our 

 standard, the growth in length per second is equal to X. 

 This will give us some idea of the sensitiveness of 

 the Crescograph employed in recording the movement of 

 growth. 



GROWTH-SCALE. 



The Balanced Crescograph enables us not merely to 

 determine the absolute rate of growth, but the slightest 

 fluctuation in that rate. 



Indicator Scale. — All necessity of calculation is obviated 

 by the scale provided with the apparatus. The speed of 

 clockwork which brings about the balance of growth is 

 determined by the position of the adjusting screw S, the 



