EFFECT OF ELECTRIC FIELD 185 



small portable set known as the ' violet-ray apparatus.' 

 It was not difficult to get a marked response when the so- 

 called violet ray emitted by one of the electrodes struck 

 the plant. But being desirous of obtaining the pure effect 

 of the high-frequency electric field, I had a large hollow 

 spiral placed in series with the secondary of the Tesla coil. 

 The pulvinus and petiole were placed inside the spiral, 



Fig. 107. Effect of high-frequency alternating electric field 



on response of pulvinus of Mimosa. 



Note slow contractile fall with minute pulsations. 



Arrow indicates moment of stimulation, arrow within circle 



its cessation. 



a portion of the petiole projecting out of it for connection 



with a recorder. 



With a very sensitive specimen of Mimosa the response 

 was an excitatory fall, the responsive reaction being induced 

 within 10 seconds of the incidence of the stimulus. The 

 contraction in this case was slow and gradual as under the 

 action of light, and not abrupt as under an electric shock. 

 The contraction persisted for a time after the cessation 

 of stimulation, after which there was a gradual recovery 

 (fig. 107). 



