208 COMPARATIVE ELECTRO-PHYSIOLOGY 



The average period of each pulsation is here about thirty 

 seconds ; but this may vary in different cases from half of this 

 to one minute. I have also been able to detect these multiple 

 excitatory waves, during their transit through non-motile con- 

 ducting tissues such as stems. The imperceptible volumetric 

 changes which occur on the arrival of excitation were here 

 detected electrically by variations of pressure induced in an 

 enclosing microphonic contact. In fig. 136 is seen such 



FIG. 135. Multiple Mechanical Response of Biophyhim^ due to a Single 

 Strong Thermal Stimulus 



multiple electro-tactile response in the stem of Mimosa, due 

 to a single thermal stimulus. 



I have also been able to record such multiple excitatory 

 effects by means of electro-motive response. In fig. 137 is 

 seen a photographic record of a series of such responses, 

 given by the leaf of Biophytum, the individual thermal 

 stimuli being here applied at intervals of five minutes. It will 

 here be noticed that each single stimulus gave rise to 

 from five to eight responses, the average period of which 

 was thirty seconds. From the corresponding mechanical 



