44 



CHAP. V. EFFECT OF CHEMICAL AGENTS 



Effect of Carbonic Acid Gas 



Experiment 15. — The immediate effect is a very marked 

 acceleration of growth. With a seedhng of Onion (Alhum) 

 the increase was found to be two and a half times. With 



the flower-bud of Crinum the rate 

 was enhanced threefold, from the 

 normal o -25 [x to 0-75 Jjl per second. 

 After the preliminary enhancement, 

 there was a depression of growth 

 within 15 minutes of the application, 

 the rate being now reduced to • 15 a 

 per second (fig. 18). These effects 

 taking place equally in light and 

 darkness prove that the phenomenon 

 is independent of photosynthesis. 

 The immediate and subsequent effects 

 of CO2 on growth have already been 

 demonstrated by the highly sensitive 

 method of balance {cf. fig. 13). 



Fig. 18. Effect of Car- 

 bonic Acid Gas on 

 growth. 



a, normal rate ; b, en- 

 hanced rate as the 

 immediate effect ; c, 

 retarded rate after pro- 

 longed application 

 (Crinum). 



Effect of Vapour of Ether 



The following may serve as typical 

 examples of results obtained with 

 various plants. Among these may 

 be mentioned the seedlings of Wheat ; 

 stems of Helianthus and of Dahlia ; 

 petiole of Tropaeolum ; tendril of Cucurbita ; peduncles of 

 Hibiscus, Centaurea, Daffodil, and of Allium ; the flower- 

 bud of Crinum Lily and the pistil of Datura. The effects 

 observed were essentially similar in all cases, of which three 

 representative examples will be described in detail. 



Experiment 16. Seedling of Wheat. — The specimen was 

 an intact seedling with roots ; it exhibited a fairly rapid 

 rate of growth, as shown in the first part of the record. On 



