EFFECTS OF DRUGS ON PLANTS 



483 



Fig. 196. Spasmodic Alternations 

 of Growth under Alcohol 



at the next a sudden depression, such alternations being 

 continued for a considerable length of time. On repeating 

 the experiment at the higher temperature of 34 C. I found 

 that these spasmodic alterna- 

 tions became still more violent — 

 that is to say, of greater ampli- 

 tude, though less frequent. At 

 a much higher temperature, how- 

 ever, the effect of alcohol was 

 an immediate depression. Still 

 stronger solutions caused arrest 

 of growth at all temperatures. 



Effect of acids. — We found, in the case of the autono- 

 mous responses of Desmodium, as of cardiac muscle, that 

 acids induced relaxation, and that the long-continued action 

 of such a reagent, or a strong solution, would bring about 

 arrest in the relaxed position. Curiously enough, then, in 

 the case of growth, which I have shown 

 to be an instance of multiple or autono- 

 mous response, I find an effect exactly 

 parallel. In order to hasten the result 

 I used a somewhat strong solution, 

 namely 4 per cent., of hydrochloric acid. 

 This, as will be seen (fig. 197), caused 

 a marked relaxation, and growth came 

 to a standstill some six minutes after- 

 wards. In this experiment, and the 

 following on the effect of alkali, the 

 record was taken under unbalanced 

 conditions. 



Effect of alkali. — The effect of alkali in the case of Des- 

 modium, and also of cardiac muscle, is to produce arrest in 

 the contracted position ; a similar effect is strikingly exhi- 

 bited in the growth-record given in fig. 198. The first part 

 of this record shows the normal rate of growth. A 3 per 

 cent, solution of sodium hydrate was then applied at the point 

 marked with the downward arrow {}), It will be noticed 



FIG. 197. Unbalanced 

 Record showing Ac- 

 tion of Acid in Causing 

 Relaxation and Ulti- 

 mate Arrest of Growth 



