COMPARATIVE ELECTRO-PHYSIOLOGY 



arrangement, the galvanometer is kept open, and closed only 

 during 'Oi of a second at the required increasing intervals of 

 time. 



There may be a pre-existing difference of potential 

 in the plant, as between the two points of galvanometric 

 contact, N, and N 2 . In order that this may not be a source 

 of disturbance, a compensating potentiometer arrangement, 

 C, is employed. The slider of the compensator is so adjusted 

 that it exactly balances the resting difference of potential 

 in the specimen. Under these circumstances, neither make 

 nor break of the galvanometer occasions any deflection. And 

 this balance is readjusted for each experiment of the series. 



I give below two tables which summarise rheotomic 

 observations on specimens of the petiole of cauliflower. By 

 successive intervals of a given length should always be under- 

 stood the mean interval : that is to say, the period between the 

 application of stimulus and the mid-point in the removal of 

 the short circuit. Thus, for the mean interval of -02 of a 

 second, the middle of the striking-rod B, whose breadth is 

 i cm., placed at a distance of 2 cm. from A. The galvano- 

 meter is therefore acted on for 'Oi of a second, throughout 

 the period from '015 to '025 of a second, after stimulation. 

 In the first two sets of results here given, the observations will 

 be seen to have been taken at the somewhat long intervals 

 of *i of a second. The stimulus applied in these cases was 

 moderate. In the case of a third specimen, the observations 

 on which will be given subsequently, the results were recorded 

 at intervals of 'Oi of a second. 



SPECIMEN I SPECIMEN II 



