32 CHAP. III. THE BALANCED CRESCOGRAPH 



of the experiment the curve becomes once more horizontal, 

 it indicates the resumption of the normal rate. The follow- 

 ing results give a striking demionstration of the influence of 

 the time-factor. 



Experiment 9. Effect of Carbonic Acid Gas on growth. — 

 After obtaining the balance of growth with a seedling 

 of Wheat, the plant-chamber was filled with CO2 diluted 

 with air, the moment of application being marked with an 

 arrow in the record. There was an almost immediate 

 acceleration of the rate of growth, the latent period being 

 less than 5 seconds. This enhanced rate continued for 

 120 seconds, slowing down gradually to the normal and 

 remaining so for 20 seconds as indicated by the horizontal 

 record at the top of the curve. Continued action of CO2 

 induced, however, an inversion of the curve, the down- 

 record indicating a rate below the normal (fig. 13). Strength 

 of dose exerts its characteristic influence, very dilute CO2 

 inducing acceleration, while stronger concentration or longer 

 application of the gas brings about a quick reversal 

 from acceleration to retardation, culminating in arrest of 

 growth. 



Two different methods are thus available for investi- 

 gations on growth ; the ordinary Method of Crescographic 

 Magnification, and the excessively sensitive Method of 

 Balance. The results obtained by the second method will 

 be found not merely to confirm those obtained by the first, 

 but also to afford important information regarding the 

 influence of the time-factor in its relation to growth. 



Summary 



In the Method of Balance the upward movement of 

 growth is compensated by a corresponding subsidence of 

 the plant. Two different methods of balance have been 

 successfully employed : (i) that of the Falling Weight, 

 and (2) that of the Inclined Plane. 



In the condition of balance, the record remains horizontal. 



