POLAR EFFECTS OF MODERATE CURRENTS 213 



Fourth, the leaflets of Averrhoa caramhola are only 

 moderately sensitive. They close downwards on excitation. 



Fifth, the leaflets of Averrhoa hilimhi possess more or 

 less the same kind of excitability as A. caramhola. Under 

 excitation these leaflets fold downwards. 



Sixth, and lastly, we have the primary pulvinus of 

 Mimosa whose polar reactions have already been briefly 

 referred to. In this and a subsequent chapter I shall 

 give a more exhaustive series of experiments in connection 

 with the response of the leaf of this plant. 



These practically exhaust the list of plant-organs possessed 

 of sensitiveness sufficient for our purpose. It will be my 

 object in this chapter to give a detailed description of the 

 reactions of these various specimens. 



We shall find that the character of the reaction will 

 depend on the intensity of the electrical current. With a 

 feeble current a characteristic effect is induced which will 

 be designated as that of Type I. As the acting e.m.f. is 

 gradually increased, the effect is transformed into that of 

 Type II. The characteristic effects of feeble and moderate 

 currents on various sensitive plant-organs will now be dealt 

 with in some detail. 



In these experiments, I shall generally speaking employ 

 the Bi-polar method, which possesses many advantages 

 over the Mono-polar method already described. In the 

 Bi-polar method the electrical contacts are made with two 

 points, at or near two different motile-organs. When the 

 commutator is turned to the right, the right contact is 

 suddenly made kathode and the left anode. We are now 

 able to note the excitatory effects, if any, at kathode-make, 

 Km, to the right, and at anode-make, A'm, to the left. The 

 dash affixed in this latter case will always be used to distin- 

 guish the contact on the left side. The circuit is now broken, 

 and we observe the effects of kathode-break, Kb, and anode- 

 break, A'b. The commutator is next tilted to the left, 

 making the right anode, and enabhng us to note the effects of 

 K'm and Am. The circuit is then broken, producing the 



