482 PLANT RESPONSE 



induce contraction, which would in the present case take 

 the form of a transient retardation of growth. 



Effect of solution of sodium carbonate. — In the course 

 of the following experiments the chemical reagents are 

 administered internally, by applying the solution at the cut 

 end of the specimen. A dilute solution of sodium carbonate 

 is known to increase excitability in the case of animal tissues. 

 I find that this holds good in the case of the growth-response 

 of plants, growth being accelerated, as will be seen in 

 fig. 194, where the balanced record suddenly gives place to 

 an ascending curve. But in the case of chemical reagents in 

 general, and of this especially, it must be remembered that 

 the strength of the solution, or dose, is an important element 

 in the result. A -5 per cent, solution of sodium carbonate 

 was always found in these experiments to be an excitant ; 

 but as the strength of the solution was increased, the excita- 

 tory effect was found to be gradually diminished, until at 

 2 per cent, it became neutral. If 

 now the strength were still further 

 increased, say to 5 per cent., the 

 effect was an actual depression of 

 the rate of growth. 



Effect of solution of sugar.— I 

 next give a record (fig. 195) showing 

 the effect of the application of sugar 

 Fig. 195. Acceleration of jn a 2 per Cent, solution. This is 



Growth by Application of 



Solution of Sugar seen to mduce a responsive accelera- 



tion of growth. In the case of the 

 Crinnm Lily, this acceleration is found to occur even under a 

 5 per cent, solution of sugar ; but very much stronger solu- 

 tions induce depression. 



Effect of alcohol. — We have hitherto observed different 

 reagents- inducing a more or less uniform acceleration or 

 depression. In the case of alcohol, given in 5 per cent, 

 solution, however, we obtain a very curious instance of 

 alternating spasmodic effects (fig. 196) ; that is to say, the 

 growth at one moment exhibits a sudden acceleration, and 



