GENERAL SURVEY 351 



the experiments of Pfeffer and Haberlandt, who found 

 transmission of stimulus to take place in spite of narcotisa- 

 tion or scalding of the intervening tissue. It is shown that 

 those experiments are not conclusive, inasmuch as super- 

 ficial narcotisation or scalding is not effective in abolish- 

 ing the conducting power in the interior of the tissue. 



For the settling of the question whether the transmission 

 is physical or physiological it was necessary to have quanti- 

 tative measurements of the highest accuracy in order to 

 determine whether physiological changes affect in a definite 

 manner the velocity of transmission. For the accurate 

 determination of velocity it is essential to allow for the 

 latent period of the responding pulvinus and its variations 

 under different conditions. 



Determination of Latent Period 



By the employment of the Resonant Recorder the value 

 of latent period can be accurately determined within a 

 hundredth part of a second. Successive determinations of 

 the latent period under constant external conditions are 

 found to give identical results. The shortest value of the 

 latent period in vigorous Mimosa is -06 second, the average 

 value in summer being 'i second. The latent period is in 

 general shorter under stronger intensity of stimulus ; but 

 the value becomes constant above a maximal stimulus. 

 In the optimum condition of the plant the latent period 

 is the same for feeble or strong stimulus. Fatigue prolongs 

 the latent period ; a rise of temperature, on the other hand, 

 shortens the latent period (p. 130). The latent period of the 

 pulvinus of Neptunia oleracea is '6 second. 



Determination of Velocity of Transmission of 

 Excitation 



Successive values of velocity of transmission are found 

 constant when the applied stimulus is constant, and when 

 the intervening period of rest allows complete protoplasmic 

 recovery. Consistent results have been obtained by the 



