GEO-BLECTRIC RESPONSE OF ROOT 



471 



The series of experiments were carried out iu the 

 following order. The specimen was first rotated through 

 + 90° so that A was above. The responsive electric varia- 

 tion rendered it galvanometrically positive. The root was 

 rotated back to neutral position when tlie current dis- 

 appeared. The root was next rotated through - 90^ and 

 the responsive current became reversed, the upper B becom- 

 ing electro-positive (Fig. 173). The alternative rotations 

 through 4-90° and -90° were carriful out six times in 

 succession with consistent results. The interval allowed 

 between one stimulation and the next was determined by 

 the period of complete recovery. Growing fatigue was 



Aj,B 



-(TV < 





1 



Fig. 173. — Diagrammatic representation of geo-electric response of growing 

 region of root, (a) Rotation tlirongh -90^ malses B, galvanometrically positive. 

 (b) Vertical and neutral position, (c) Rotation through +90"' places A above anci 

 renders it galvanometrically positive, (d) Additive effect on current of response, 

 root-tip a negative, and growing region A positive. 



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

 at the second repetition it was ten minutes, and at the 

 third time it was prolonged to fifteen minutes. 



I give l)elow the series of electric responses induced by 

 alternate rotations through -|-90^ and -90°. The upper 

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



35 



