110 THE SIGNS OF LIFE [LECT. 



when points of both surfaces act against each other through the 

 galvanometer? If to both directions of excitation, the resultant 

 is in one, say, a descending direction, we may be pretty sure 

 that the upper surface reacts more powerfully than the lower 

 surface ; but to make quite sure, it is better to take two pairs of 

 tests, reversing the order of direction in each pair, i.e., to take 

 the responses after excitations B to A, A to B, and after excita- 

 tions A to B then B to A, because it may well happen with 

 excitations of any considerable strength that the first is greater 

 than a second excitation, and we are not assured that a differ- 

 ence thus caused might not disturb a comparison. 



Homodrome post-anodic of upper surface greater than 

 Antidrome post-kathodic of lower surface ; therefore A | ^ 



Homodrome descending response A to B. [ ~Y\ 



B ~pt 

 Antidrome post-kathodic of upper surface greater than 



Homodrome post-anodic of lower surface ; therefore 

 Antidrome descending response A to B. 



A result of this character clearly proves that the blaze of 

 the upper surface of a leaf (beside geranium I have also tested 

 lilac and violet leaves) predominates over the blaze of its lower 

 surface. The ingoing current of the upper surface, whether 

 anodic or kathodic, has exceeded the ingoing current of the 

 lower surface, whether kathodic or anodic. We must be careful, 

 however, to secure equal areae of the two exciting electrodes (see 



6 9> 



67. Anodic versus Kathodic blaze. You ask again, whether, 

 cceteris paribus, an anodic or a kathodic blaze is the greater. 



To answer this question, you only 

 require to make a sufficient number 



, of trials in which the two currents 



x * are opposed to each other from points 



Eacc. > on one surface. You apply, e.g., your 



' sp ' two electrodes to the upper surface 



(or to the lower surface), and find 



that the after-effect is homodrome with the exciting current. 

 You conclude that normally the post-anodic ingoing homodrome 

 blaze exceeds the post-kathodic ingoing antidrome blaze. 



B 



