POLAR EFFECTS OF MODERATE CURRENTS 225 



the sensibility is much less than that of the leaflets of 

 Mimosa and Biophytum, will next be described. Amongst 

 these the first plant dealt with is Neptunia. 



Leaflets of Neptunia 



This plant is somewhat like Mimosa pudica in appear- 

 ance, except that under natural conditions in Bengal it 

 grows in water, being an inhabitant of the pools amongst 

 the ricefields. In these circumstances it develops curious 

 growths on the stem, which serve as floats. The leaves are 

 much longer than those of Mimosa, but considerably less 

 sensitive. There are three pairs of sub-petioles, which are 

 articulated to the main petiole. Electrical connections are 

 made with two points at the middle of two sub-petioles which 

 carry numerous leaflets. The sensitiveness of the leaflets 

 'of this plant is much less than in Mimosa. The conducting- 

 power is also very moderate, the velocity of transmission of 

 excitation in one of the sub-petioles being 1*5 mm. per second. 



Efect of feeble current. — The minimum e.m.f. which will 

 induce excitation is higher in the case of Neptunia than 

 in Mimosa, being 20 volts in the typical instance now to 

 be described. The resulting current was 7 micro-amperes. 

 On going through the usual cycle of direct and reverse 

 experiments, it was found that the kathode alone excited 

 during make. From experiments with five other specimens 

 I obtained the same result without exception. 



Table VI. — Effect of Feeble Current on Leaflets of Neptunia 

 E.M.F. = 20 volts ; current = 7 micro-amperes 



Effect of moderate current. — Continuing to increase the 



9 



