326 



PLANT RESPONSE 



are found to cause an arrest of the rhythmic movements of 

 Desmodium. It is not necessary to go into these in detail, 

 the experiments already given affording sufficient informa- 

 tion for their successful repetition. 



I will only mention here the very interesting and impor- 

 tant fact, that I find acids and alkalies, generally speaking, 

 to produce effects which are in a certain physiological sense 

 antagonistic. These effects, together with the influence of 

 temperature on rhythm, and the action of tetanising electric 

 shocks on the autonomous movements of Desmodium, will be 

 found fully described in Chapters XXVI. and XXVII., where 

 the remarkable parallelism of their influence on rhythmic 

 animal and vegetable tissues will be demonstrated. I shall con- 

 clude the present chapter by describing the action of a strongly 

 poisonous reagent on the pulsatory movements of Desmodium. 

 Effect of copper sulphate solution. — I carried out two 

 experiments on similar specimens to test the effect of 



this reagent. In the 

 first, the solution was 

 applied directly on the 

 pulvinus, and produced 

 a very quick arrest of 

 its rhythmic activity 

 (fig. 133). In the 

 second case, the ap- 

 plication was made at 

 the cut end of the 

 petiole, as already de- 

 scribed, which was at a 

 distance of 2 cm. from 

 the pulvinus. In this 

 case the arrest took 

 place much later, that 

 is to say, thirty minutes after the application. This delay was 

 due to the fact that the poisonous solution had to ascend 

 the intervening distance before it could affect the rhythmic 

 activity of the tissue at the pulvinus. This experiment will 



Fig. 133. Photographic Record of Effect of 

 Copper Sulphate Solution Applied on the 

 Pulvinus 

 Arrow marks moment of application. 



