206 



PLANT RESPONSE 



more than a dozen instances, out of which I shall give an 

 account of two. 



In the first of these, the two electric contacts were made 

 on the same leaf, at a distance of 5 cm. from each other. At 

 make, using an E.M.F. of 220 volts, excitation was produced 

 at the anode only, and the depression of successive leaflets 

 proceeded towards the kathode, but was arrested at one pair 

 in advance of that point, the kathode apparently acting here 

 as a depressor. 



In the second experiment, the electric contacts were made 

 at a great distance from each other, with middle points of two 

 opposite leaves. At make, excitation was produced at the 

 anode only. At break, however, it took place at the kathode 

 and not at the anode. We have here a complete reversal 

 of the normal polar effects under the action of very high 

 E.M.F. 



The following tabular statements show at a glance the 

 polar effects at both A and B stages, under a high E.M.F. : 



Table showing Effect of High E. M.F.— .^ Stai^e. 



Make 



Break 



Make 



Moderate response Occasional response Moderate response 



Break 



Occasional response 



Table showing Effect of Excessively High E.M.F.— j5 Stage. 



Law of polar effects under high E.M.F. — We have now 

 traced out that process of continuous change by which under, 

 a gradually increasing E.M.F. there is produced a reversal of 

 normal polar effects, and we thus arrive at the following law 

 of polar excitation : 



