204 RESEARCHES ON IRRITABILITY OF PLANTS 



pulvinus is the indicating motile organ. The paralleHsm 

 of the two cases will be clearly understood by reference 

 to fig. io8. 



With both ascending and descending currents of feeble 

 intensity I have obtained with Mimosa excitatory effects 

 at make exactly corresponding to the effects in a nerve-and- 

 muscle preparation. In order to prove that the excitation 

 is really due to make of the proximal kathode in the case of 

 descending, and of distal kathode in that of ascending, 



A -^K 



Fig. io8. — Excitation by descending or ascending currents in nerve- 

 muscle and petiole-pulvinus specimens. Motile organs are to the 

 left. Nerve-muscle (upper figure) ; petiole-pulvinus (lower figure). 



currents, I took time-records of these, as seen in fig. 109. 

 The proximal electrode was placed at a distance of 2*5 mm. 

 and the distal at a distance of 15 mm. from the pulvinus. 

 The distance between the two electrodes was therefore 

 12 "5 mm. The time-record was taken in the usual manner, 

 the vibrating recorder employed having a frequency of 

 20 vibrations per second. The appHed e.m.f. was 6 volts. 

 The two records were obtained successively, the upper being 

 the one due to descending, and the lower to the ascending, 

 current. An inspection of the records in fig. 109 at once 

 shows that the response with descending current, the 

 kathode being proximal, took place the earlier of the two. 

 Theoretically the difference between the two time- 



