42 PLANT RESPONSE 



A pulse of positive turgidity-variation is often propagated in 

 consequence of the sudden expulsion of water from a stimu- 

 lated point at a distance. 



The laws of true electric response to excitation may be 

 summarised as follows : 



A. The indirect effect of stimulation is a positive electrical 

 variation, indicating a positive turgidity-variation. 



P>. The direct effect of stimulation causes negative turgidity- 

 variation, concomitant with a negative electrical variation. 



(i) The direction of this responsive current in plant- 

 tissues, as in animal, is from the more to the less 

 excited portions of the tissue ; or, the excited point 

 is galvanometrically negative. 



(2) On simultaneous excitation of two points, the current 



of response in the tissue is from the more to the less 

 excitable. 



(3) Conversely, if the responsive current be from A to B, 



the point A may be taken as the more excitable. 



