geo-electric response op shoot 451 



trical or zero poi-ition. On rotation through + 1)0° (figure 

 to the right) A occupies the upper ami B the lower 

 position. A is seen to exhibit induced change of gaiva- 

 nometric negativity. Rotation through - 90° reverses the 

 current of response, as B now occupies the upper and A 

 the lower position. 



CHARACTERISTICS OF GEO-ELECTRIC RESPONSE. 



There are certain phenomena connected with the elec- 

 tric response under geotropic stimulus which appear to be 

 highly significant. According to statolithic theory 



" Geotropic response begins as soon as an organ is deflect- 

 ed from its stable position, so that a few starch-grains 

 press upon the ectoplasts occupying the walls which are 

 underneath in the new position ; an actual rearrangement 

 of the starch-grains is therefore not an essential condition 

 of stimulation. As a matter of fact, the starch-grains do 

 very soon migrate on to the physically lower walls, when 

 a positively or negatively geotropic organ is placed hori- 

 zontally, with the result that the intensity of stimulation 

 gradually increases attaining its maximum value when all 

 the falling starch-grains have moved on to the lower region 

 of the ectoplast. The time required for the complete 

 rearrangement of the statoliths may be termed the period 

 of migration ; its average length varies from five to twenty 

 minutes in diflFerent organs."* 



Stimulation, according to the statolithic theory, is induced 

 by the displacement of the particles. The diameter of the 

 geotropically sensitive cells is considerably less than 

 O'l mm. ; and the stimulus will be perceived after the very 

 short interval taken by the statoliths to fall through a space 

 shorter than (>1 mm. This may be somewhat delayed by 

 the viscous nature of the plasma, but in anj' case the period 



* Haberlandt— /6i</— p. 698. 



