VARIATION OF POLAR REACTION 



269 



e.m.f. being the same as before — namely, 16 volts. It 

 will be remembered that before tetanisation 16 volts, though 

 effective for Ab excitation, had been ineffective for Am 

 excitation. After tetanisation, however, the Am excitation 

 became effective. The after-effect of moderate stimulation 

 had thus been to transform Km Ab, the polar reaction of 

 Type II., to Km Am Ab of Type III. 



As already mentioned, from the point of view of stimulus 

 the youngest green leaf at the top of the plant, say Li, 

 may be regarded as being in a sub-tonic condition. A leaf 

 lower down, L2, must be taken as having been previously 



Table IV. — Simultaneous Action of Currents of Increasing 

 Intensity on a very young Li, and a slightly older Leaf L2 



subjected to moderate stimulation. From the experiment 

 just described, then, we should expect that one identical 

 current would evoke response of a higher type from L2 

 than from Li. 



In order to test this inference I took a plant and made 

 bi-polar connections with the second and fourth leaves from 

 the top, the former of these being very young. Besides 

 these, a second pair of bi-polar connections was also made, 

 between the fifth and seventh leaves in descent, and these 

 will be referred to as L3, which was old, and L4 which was 

 very old. The results obtained from the second pair will 

 be dealt with separately. 



Above I give a tabular statement of the results obtained 



