THE BALAXCED CRESCOGRAPH 265 



sensitive arrangement is sufficient. I give below accounts 

 of several typical experiments in which the recording form 

 of Crescograph was employed, the raagnilication being only 

 2,000 times. 



Effect of carbonic acid on Balanced growth : Experiment 

 100. — I have already shown that carbonic acid diluted with 

 air induces an enhancement of the rate of growth, but its 

 long continued action induces a depression (p. 185). I 

 shall now employ the Method of Balance in studying the 

 effect of CO., on growth. It should be remembered in this 

 connection that the horizontal record indicates the balance 

 of normal rate of growth. An up-curve exhibits the 

 induced enhancement and a down-curve, a depression of 



Fig. 96. — Record showing the effect of CO.^. Horizontal line at beginning 

 indicates balanced growth. Application of CO^ at arrow induces enhancement 

 of growth shown by the up-curve followed by depression, shown by the down- 

 curve. Successive dots at intervals of 10 seconds. (Seedling of wheat.) 



growth. In the present experiment after obtaining the exact 

 balance, pure carbonic acid gas was made to fill up the 



22 a 



