CHAPTER IV 



OBSERVATION BY RHEOTOME ON ELECTRIC RESPONSE 

 IN PLANTS 



Response - curve showing general time - relations Instantaneous mechanical 

 stimulation by electro-magnetic release Arrangement of the rheotome 

 Tabular statement of results of rheotomic observations Rhythmic multiple 

 responses. 



IN taking records of the electric response of plants, a 

 galvanometer of fairly high sensitiveness is required. One 

 which gives a deflection of I mm. at a scale-distance of 

 I metre, under a current of io~ 9 ampere is found, as already 

 said, to be suitable for practical purposes. I used for most of 

 /[the experiments in this work a dead-beat galvanometer of 

 I the D'Arsonval type. The natural period of swing in these 

 ' galvanometers is somewhat long, however, and the response- 

 record thus lags behind the electro-motive changes induced 

 by stimulus. 



In order, therefore, to investigate the time-relations of a 

 growing electro-motive reaction in a plant, after the recep- 

 tion of the stimulating shock, it is necessary to employ a 

 rheotomic mode of investigation. An account of this, and 

 of the results obtained, will be given in the course of the 

 present chapter. The after-effect of stimulus is found to 

 be somewhat persistent and to vary in duration in different 

 specimens. In some cases, recovery is complete in a very 

 short time ; in others it takes very much longer. For the 

 purpose of forming a general idea of this difference two 

 response-records are given here, one of which was taken from 

 a stem of the quickly-reacting Amaranth (fig. 35), and the 

 other from the more sluggish Colocasia. It will be seen that 



