POLAR EFFECTS OF MODERATE CURRENTS 22t 



that of the second type. With older specimens, the first 

 type may persist up to 12 volts. 



Taking an excitable specimen of leaflets of Mimosa, 

 I first applied 4 volts and obtained with it Type I. effect, 

 that is to say, excitation took place only at the make of 

 the kathode. I then raised the e.m.f. to 8 volts. At make, 

 the kathodic point on the right became the seat of excitation, 

 four pairs of leaflets undergoing closure in the extra-polar 

 and six pairs in the intra-polar regions. There was no 

 effect at the anode. At break, however, excitation was 

 initiated at the anode, as evidenced by the serial closure 

 of three pairs of leaflets in the intra-polar and two pairs in 

 the extra-polar regions. This effect was corroborated by a 

 reversal experiment, when the new kathodic point to the 

 left exhibited excitation at make, and the new anodic point 

 to the right exhibited it at break. Thus with current of 

 moderate intensity, excitation took place in the sub-petiole 

 of Mimosa at the make of kathode and break of anode. 

 The polar excitation formula of the leaflets of Mimosa under 

 moderate current may therefore be expressed as KCC, AOC ; 

 or Km Ab. 



Table III. — Leaflets of Mimosa under Moderate Current 

 E.M.F. = 8 volts ; current = i-6 micro-ampere 



I carried out this experiment on the polar effects of a 

 moderate current on leaflets of Mimosa with twenty-five 

 different specimens, and obtained invariably the charac- 

 teristic effects of excitation only at the make of kathode 

 and the break of anode. 



