EFFECTS OF DRUGS ON PLANTS 489 



Carbonic acid gas induces a preliminary acceleration, 

 followed by retardation and arrest of growth. On re- 

 admission of fresh air growth is revived. 



Ether, when applied internally, causes a preliminary 

 acceleration, followed by retardation and arrest of growth. 

 Minor differences of effect may be observed if the applica- 

 tion be made externally. 



A very dilute solution of sodium carbonate is an exci- 

 tant, and accelerates growth ; but stronger solutions cause 

 retardation. 



Solution of sugar also stimulates growth, if the strength 

 of solution be not excessive. 



Alcohol causes spasmodic alternations of growth. Too 

 strong a solution arrests growth. 



As in the case of autonomous response of Desmodium y 

 so in the response of growth also, acids and alkalis are 

 found to have antagonistic effects. Acid causes relaxa- 

 tion and ultimate arrest of growth ; alkali causes arrest 

 of growth in the contracted position. The arrest brought 

 about by one of these agents may be counteracted by the 

 other. 



The reaction of a specimen to a chemical reagent is 

 determined by the strength of the dose, and by the duration 

 of application. 



A stimulating agent if given in too strong a dose causes 

 depression. A poisonous reagent, again, if given in a suffi- 

 ciently small dose, acts as an excitant. 



A clear insight into the nature of ' constitution,' so called, 

 as a factor in determining the reaction of a specimen to a 

 given drug, is afforded by the induction of definite arti- 

 ficial constitutions. This may be carried out by subject- 

 ing the plant to four different typical temperature con- 

 ditions—the ordinary, the optimum, post-optimum, and 

 maximum. 



It is then found that a plant which has been made to 

 acquire excess of internal energy can struggle against, or 

 even overcome, the influence of such adverse circumstances as 



