314 CHAP. XXIX. GEO-ELECTRIC RESPONSE OF THE SHOOT 



negativity, I have been working for many years to find 

 an independent means of recording the effect of geotropic 

 stimulation by means of electric response. The character- 

 istic electric record is modified, as is the mechanical record, 

 by the bending down of the stem which precedes the geo- 

 tropic up-movement. I was able to eliminate this com- 

 phcating factor by restraining all movement of the shoot, 

 the responsive change of galvanometric negativity being 



an independent expres- 



M 



E 



C 



excitatory re- 

 The following 



E 

 M 



E' 

 C 



sion ol 

 action. 



account is quoted from 

 my previous work pub- 

 lished in 1907 : ^ 



' The secondary effect, 

 due to mechanical dis- 

 turbance, which masks 

 for a time the excitatory 

 effect of gra\'itational 

 stimulus, may thus be 

 eliminated completely by 

 restraining all movement 

 of the shoots. The pro- 

 blem thus resolves itself 

 into the fixing of an ex- 

 perimental shoot — say, the peduncle of Eucharis Lily — in 

 such a way that mechanical response is completely restrained. 

 The next point is to subject the specimen at a given 

 moment to the stimulus of gravity, and to record the 

 consequent electric response. 



' It is clear that when any two points are acted on 

 symmetrically by the force of gravity, there is no resultant 

 geotropic action. This is the case in regard to two diametric- 

 ally opposite points A and B situated laterally on an erect 

 shoot. When the shoot is laid horizontally, two lateral 

 points are like^^'ise acted on s}Tiimetrically by the force of 



1 Comparathe Electro-Physiology , p. 442. 



Fig. 1 89. Diagrammatic representation 

 of a multicellular organ laid hori- 

 zontally and exposed to geotropic 

 stimulation. 



In the upper half, the statoliths act on 

 the protoplasm lining the inner side of 

 the tangential wall e ; in the lower 

 half they act on the protoplasm lining 

 the outer side of the tangential wall of 

 e'. (After Francis Darwin.) 



