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, 

 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 



