370 



CHAP. XXXIII. THE RESPONSE OF THE ROOT 



by the period of complete recovery. Growing fatigue 

 was found to increase this period ; at first it was 7 minutes, 

 at the second repetition it was 10 minutes, and at the third 

 time it was prolonged to 15 minutes. 



A.B 



1 



B 



L0J 





Fig. 213. Diagrammatic representation of geo-electric response 



in growing region of root. 



a, rotation through — 90° makes b galvanometrically positive. 

 b, vertical and neutral position, c, rotation through 

 -f- 90° places A above and renders it galvanometrically 

 positive, d, additive effect on current of response, root- 

 tip a negative and growing region a positive. 



I give below the series of electric responses induced 

 by alternate rotation through + 90° and — 90°. The 

 upper position was occupied by A in the odd series, and by 

 B in the even series. In every case the upper side became 

 galvanometrically positive. 



Table XXXVI. — Geo-Electric Response of Root in the 



Region of Growth. 



Additive Action-Current at the Tip and at the 



Growing Region 



It has been shown that under geotropic stimulation 

 the upper side of the tip a, being directly stimulated, be- 

 comes galvanometrically negative ; while the indirectly 



