378 



COMPARATIVE ELECTRO-PHYSIOLOGV 



I. The water in the plant-vessel may be supposed to undergo 

 decomposition by electrolysis. There may also be a certain 

 evolution of heat in the plant-vessel. 2. In a sluggish 

 tissue, such as that of the plant, the excitatory value of 

 induction-shocks may not prove sufficient to modify suctional 

 response. 



With regard to the first of these objections, it is to be 

 borne in mind that the shocks, being alternate, will produce 

 but little polarisation effect. The heating effect of a current 

 so small in quantity, moreover, is also likely to be very 



slight. The extent of 

 the disturbance from 

 these causes can, how- 

 ever, be determined by 

 a blank experiment. 

 The electrodes, by 

 whose proper applica- 

 tion the plant is ex- 

 cited, are allowed to 

 hang down in the plant- 

 vessel without direct 

 attachment to the plant 

 itself. The alternating 

 current will now pass 

 through the water, only 

 a very small fraction of 



FIG. 223. Record of Blank Experiment showing 

 Absence of any Disturbance of Record from 

 Induction -shocks as such 



Photographic record of excursion of mercury 

 index in Shoshungraph. The thick white 

 line shows duration of application of shock. 

 Time-marks in this and other photographic 

 records represent intervals of five minutes. 



it, incapable of pro- 

 ducing effective excitation, passing through the plant. 

 The Shoshungraph is adjusted for the balanced condition, 

 given as we have seen, a horizontal line of record, and 

 that intensity of induction-current which is to be used 

 in subsequent experiments is now passed through the 

 plant-vessel for twenty minutes continuously. It will be 

 seen from the record (fig. 223), that no disturbance was 

 induced by this in the balanced line, thus proving that such 

 disturbing effects, if they exist, are in practice negligible. In 

 actual experiments, where the excitatory effect is to be studied, 



