302 PROF. Je C. BOSE ON ELECTRIC RESPONSE IN 
tissue at the two leading contacts and the contiguous surface. 
In all these experiments an external resistance of one million 
ohms was always interposed, so that any slight variation of 
resistance that might be produced by the addition of a reagent 
would be quite negligible compared with the total resistance of 
the circuit. That the addition of a reagent did not produce any 
variation in the total resistance was independently verified by 
taking the deflection due to a definite small E.M.F. before and 
after (see the vertical lines to the left and right of fig. 25) the 
application of the reagent: the deflection showed no variation. 
Effect of Potash.—The next record (fig. 25) shows the depression 
Fig. 25, 
Before. After. 
of response by solution of potash. In connection with this I 
observed the curious opposite effects of poisonous reagents 
when given in small and in large doses, a peculiarity which is 
also sometimes exhibited by animal tissues. While large doses 
of potash produce abolition of response, a small dose was found 
to exhibit a stimulating action. 
Conclusion. 
The main object of my paper has been to show that the mode 
of investigation described, offers a very delicate and trustworthy 
means for the study of various intricate problems in plant- 
physiology. It has been shown how the electric record gives 
us an immediate and unfailing indication of the modification 
of the plant’s vital activity under the influence of various 
external agencies. 
