136 RESEARCHES ON IRRITABILITY OF PLANTS 



is required. For our present purpose a time-measurement 

 accurate to one-tenth or one-twentieth of a second is 

 ample. 



We first obtain a series of records of indirect stimulation. 

 The two electrodes, e and e', in connection with the exciting 

 secondary coil, are applied on the petiole about lo mm. 

 apart, the proximal electrode E being at a distance d from 

 the pulvinus. The recording-plate during the course of its 

 descent completes the primary circuit of the induction coil 

 for a definite length of time, which is about one-twentieth 

 of a second. This gives rise to a definite number of alter- 

 nating shocks to the plant. The stimulus is always applied 

 at a definite instant in the descent of the plate ; hence 

 successive records on the same plate always commence on 

 the same level, the vertical line in the record indicating the 

 moment of the application of stimulus. After taking one 

 or more records of the effect of indirect stimulation, an 

 additional record is taken of the effect of direct stimu- 

 lation. This gives the latent period L of the particular 

 specimen. 



Before proceeding further I must point out the neces- 

 sity of special precautions for the perfect insulation of the 

 electrodes in connection with the secondary coil. If one 

 of these should happen to touch the table, then, even with 

 connections made for indirect stimulation, a portion of the 

 current would pass through the flower-pot holding the 

 plant and the pulvinus would be directly stimulated by this 

 escaping current or current of leakage. In my own case, it 

 was some time before I discovered that certain anomalous 

 results were to be traced to this particular source of dis- 

 turbance, at first little suspected. To overcome this diffi- 

 culty the flower-pot should be placed on a block of insulating 

 ebonite, the electrodes also being carefully insulated on 

 ebonite rods. 



I will now proceed to give the actual records obtained 

 with the arrangements detailed above. In the experiment 

 I am about to describe the specimen of Mimosa was very 



