194 



PLANT RESPONSE 



Fig. 90. Bi-polar 

 Excitation of 

 Mimosa 



quantity of electricity passing through the tissue is very 

 small, and the changes produced in the substance of the 

 specimen are therefore slight. 



The next group of experiments was carried out by the bi- 

 polar method of excitation, which enables us to make simul- 

 taneous observations of the effects at atiode and kathode. As 

 in the previous cases, the specimen used 



>i;i| for the first experiment was Mimosa, the 



I E.M.F. employed being twelve volts. 



I , Connections were made with the pulvini 



of two neighbouring leaves (fig. 90). On 

 make, the kathodic leaf-stalk fell ; there 

 was no action at the anode. At break, 

 there was no action. On now reversing 

 the electrodes and m.aking the anode 

 kathode, the leaf-stalk which had not 

 previously responded fell under kathodic excitation. There 

 was no effect on the anodic leaf-stalk, nor was there any 

 effect on either at break. 



For the succeeding experiment 1 used a leaf of Bio- 

 phytiiin and an E.M.F. of eight volts, the electrical con- 

 nections being as shown in the diagram (fig. 91). On 



completing the circuit, the 

 excitation was discharged at 

 the kathode, and the wave 

 "'^^'^T^^'iTS^ % % "n^S^ proceeded in both directions 

 Vv ^ ^ from the kathodic point, three 



pairs of leaflets being de- 

 pressed towards the stem and 

 two in the interpolar region. 

 There was no effect at break 

 at either electrode. On reversal, the new kathode, formerly 

 the anode, became the point of excitation, as evidenced by 

 the depression of contiguous leaflets. 



Similar results were obtained when excitation was 

 produced by condenser discharge. Thus with a condenser 

 having a capacity of 'Oi microfarad, charged to eight volts. 



Fig. 91. Bi-polar Excitation of 

 Biophytum 

 At make an excitatory wave proceeded 

 in two directions from kathode, 

 but none from anode. 



