234 



PLANT RESPONSE 



Fig. ioi. Demonstration of Simultaneous 

 Opposite Effects of Anode and Kathode 

 on Transmission of Excitation 



Stimulus applied in interpolar region at x . 

 Excitation is transmitted through great 

 distances in the kathodic region, but 

 limited in the anodic. 



fall of leaflets, and was only stopped by the depressing action 

 of the anode, which this time extended to a distance of two 

 pairs of leaflets to the left of A (fig. ioo). 



The next experiment was devised to show the opposite 

 effects of anode and kathode simultaneously. For this, the 



stimulus was applied in the 

 interpolar region, half-way 

 between the two. Two 

 wave-systems were found 

 to start from the excited 

 point in opposite directions. 

 That towards K not only 

 reached K, but passed 

 beyond it, causing the 

 depression of all the leaf- 

 lets, six pairs in number, 

 on that side. But the excitatory wave that travelled towards 

 A passed through only two pairs of leaflets, and was stopped 

 at a point one pair to the left of the anode (fig. ioi). 



Electrotonic variation of motile excitability. — We have 

 seen that protoplasmic excitability finds expression in, 

 among other things, the conductivity and motile response 

 of the tissue. We have seen also how the former, that is to 

 say, the conductivity, is modified in opposite ways by the 

 influence of the anode and kathode. I shall now proceed to 

 describe experiments in which the opposite character of the 

 effects at anode and kathode is still more strikingly demon- 

 strated by the exaltation at kathode, and depression at anode, 

 of the motile excitability. 



I used two pairs of electrodes, the first pair, KA, for the 

 purpose of producing stimulation ; and the second pair, K'a', 

 in order to produce variation of excitability, through electro- 

 tonus (fig. 102) ; or vice versa. The first pair was applied on 

 the stem, the kathode K being in contact with the pulvinus of 

 the lateral leaf. K'A' were applied on the petiole of that leaf. 

 The plant was very sensitive, and in order that there 

 should be no responsive fall, by the direct and unaided 



