26o RESEARCHES ON IRRITABILITY OF PLANTS 



leaflets at the particular points, in this case the two elec- 

 trodes. As regards the transmitted effects of excitation, 

 these can easily be followed by watching the serial fall of 

 leaflets. 



I shall now describe an experiment in which, the con- 

 nections being as already described, the current was increased 

 step by step to a maximum. Beginning with a current 

 of 75 micro-ampere, it was found that excitation took place 

 only at the kathode-make. When the current had been 

 increased to 2*5 micro-amperes, excitation was initiated 

 at the kathode at make and at the anode at break. In 

 these two cases we have the familiar effects of Type I. and 

 Type 11. With the same identical specimen, however, when 

 the current was raised to 5 micro-amperes it was found that 

 excitation was simultaneously initiated at the bi-polar 

 contacts, both kathode and anode, at make. The fact that 

 the anodic fall had nothing to do with any transmission of 

 excitation from the kathode was evident by the slow march 

 of the excitatory waves, sent out from the two points inde- 

 pendently, towards each other. It may be mentioned here 

 that this phenomenon can be made still more prominent 

 by selecting for experiment leaflets which are a little older 

 and not excessively sensitive. In such a case the march 

 of the two waves can be made as slow as may be desired. 



We have seen that with strong current there is excitation 

 at both kathode and anode ; on the break of the current, 

 excitation was now found to take place only at the anode. 

 Thus we have the excitatory effect of Type III. — namely 

 Km Am Ab — established independently by an experiment 

 on the leaflets of Mimosa. 



Employing the minimal current essential to the mani- 

 festation of Type III. we find the excitation at anode- 

 make somewhat localised, whereas that at kathode-make is 

 transmitted to a considerable distance. But on increasing 

 the current the power of excitatory transmission of anode- 

 make is greatly enhanced. 



Returning once more to the experiment, I found that 



