28 RESPONSE JN THE LIVING AND NON-LIVING 



(a) 



ture. On stimulating the stalk there was produced a 

 greater excitation at A than at B, and a current of 

 action was then observed to flow in the stalk from the 

 more excited A to the less excited B (fig. 6). 



But we can cause this differential action to become 

 evident by another means. For example, if we produce 

 a block, by clamping at C between A and B (fig. 14, a), 



so that the disturbance 

 made at A by tapping or 

 vibration is prevented from 

 reaching B, we shall then 

 have A thrown into a rela- 

 tively greater excitatory 

 condition than B. It will 

 now be found that a cur- 

 rent of action flows in the 

 stalk from A to B, that is 

 to say, from the excited 

 to the less excited. When 

 the B end is stimulated, 

 there will be a reverse current (fig. 14, b). 



We have in this method a great advantage over 

 that of negative variation, for we can always verify any 

 set of results by making corroborative reversal experi- 

 ments. 



By the method of jnjury again, one end is made 

 initially abnormal, i.e. different from the condition 

 which it maintains when intact. Further, inevitable 

 changes will proceed unequally at the injured and 

 uninjured ends, and the conditions of the experiment 

 may thus undergo unknown variations. But by the 



Current of response ichen 



A is stimulated^ 

 Current of response when 



B is stimulated^ 



FIG. 14. THE METHOD OF BLOCK 



(a) The plant is clamped at C, between A 



andB. 

 (6) Kesponses obtained by alternately 



stimulating the two ends. Stimulation 



of A produces upward response ; of B 



gives downward response. 



