Petiole- Pulvinus Preparations of Mimosa pudica. 221 



is normally in a state of compression, and (2) by the weight of the leaf. So 

 much for theory. The experimental evidence available regarding the relative 

 importance of the upper and lower halves of the pulvinus is not very con- 

 clusive. Lindsay attempted to decide the question by his amputation 

 experiments. He showed that when the upper half was removed the leaf 

 carried out the response, but rigor set in when the lower half was amputated. 

 Pfeffer's experiments on the subject, however, contradicted the above results. 

 He found that " after the upper half of the pulvinus was carefully removed, 

 no movement was produced by stimulation, whereas when the lower half is 

 absent a weakened power of movement is retained." Pfeffer, however, adds 

 " since the operation undoubtedly affects the irritability, it is impossible 

 to determine from such experiments the exact part played by the active 

 contraction of the lower half of the pulvinus."* 



The cause of uncertainty in this investigation is twofold. First, it arises 

 from the unknown change in irritability consequent on amputation ; and, 

 secondly, from absence of any quantitative standard by which the effect of 

 selective amputation of the pulvinus may be measured. As regards the first, 

 I have been able to reduce the depressing action caused by injury to a 

 minimum by benumbing the tissue before operation, through local applica- 

 tion of cold, and also allowing the shock-effect to disappear after a rest of 

 several hours. As regards the physiological gauge of efficiency of the motor 

 mechanism, such a measure is afforded by the relation between a definite 

 testing stimulus and the resulting response with its time-relations, which is 

 secured by my Eesonant Eecorder with the standardised electrical stimulator. 



In carrying out this investigation I first took the record of normal response 

 of an intact leaf on a fast moving plate. A second record, with the same 

 stimulus, was taken after the removal of the upper half of the pulvinus, 

 having taken the necessary precautions that have been described. Comparison 

 of the two records (fig. 4) shows that the only difference between them is in 

 the exhibition of slight diminution of excitability due to operation. But, as 

 regards the latent period and the quickness of attaining maximum fall, there 

 is no difference between the two records before and after the amputation of 

 the upper half. The upper part of the pulvinus is thus seen practically 

 to have little influence in hastening the fall. 



5. Effect of Removal of the Lower Half. 



The shock-effect caused by the amputation of the lower half was found to 

 be very great, and it required a loug period of rest before the upper half 

 regained its excitability. The excitatory reaction of the upper half is by 



* Pfeffer, ibid., p. 75. 



