192 PLANT RESPONSE 



that in the reversal experiment, what was formerly anode 

 became kathode, and vice versa. 



In this way corroborative reversal effects were obtained. 

 In experiments with condensers it was not necessary, in order 

 to reverse the electrodes, to reverse the battery connection, 

 for owing to the special arrangements of the electric circuit 

 (fig. 14) the anode at 'charge' became kathode at ' discharge.' 



In studying the effects of increasing intensity, in the case 

 of constant current, I simply add to the number of storage 

 cells, and in this way obtain increasing voltage. The strength 

 of the condenser discharge is increased by increasing the 

 voltage of the charging circuit. With the same tissue, where 

 the resistance is constant, the current increases with the 

 acting E.M.F. Hence, increasing E.M.F. here connotes also 

 increasing current. But we may have a very high E.M.F. 

 and, owing to high resistance of the tissue, only a feeble 

 current. From the trend of the various experiments that I 

 have carried out, it would appear that the characteristic polar 

 effects are determined more by the intensity of the E.M.F. 

 than by that of the current. In the case of the present 

 investigation, as we must also bear in mind, the experiments 

 were performed with many different specimens, the excitability 

 of some being greater than that of others. 



Effect of feeble E.M.F. — The first experiments of this 

 series were carried out by the method of mono-polar ex- 

 citation. The first specimen employed was Mimosa, one 

 electrode, the kathode, being connected with the pulvinus, 

 and the anode, at some distance, with the main stem. The 

 electromotive force used was ten .volts. The leaf-stalk fell 

 at make of the circuit. The leaf was found to recover, 

 after a due interval, during the continuation of the current. 

 The current was now broken, but this produced no responsive 

 effect whatsoever. The current was next reversed, the pulvinus 

 being made anode. But this anode-make did not produce 

 any excitatory effect, neither did the succeeding anode-break. 

 From these experiments we see (a) that a feeble E.M.F. 

 excites at the kathode at make ; (b) that the excitation takes 



