MECHANICAL AND ELECTRTCaL RESPONSE OF ROOT 463 



point A becomes galvanometrically negative. This shows 

 that the response of the root is in no way different from 

 that of the shoot. 



rt 



MECHANICAL RESPONSE TO INDIRECT STIMULUS. 



Before describing the effect of indirect stimulus on the 

 ^ root, I shall recapitulate its 



effects on ordinary tissues. 

 I have' shown that the 

 effect of indirect unilateral 

 stimulus is to induce a 

 movement away from stimu- 

 lus. This was shown to be 

 the case with the bud of 

 Crinum (p. 275) and the 

 tendril of Passifiora (p. 291). 

 The mechanical and electric 

 response to indirect stimu- 

 lation in the shoot is shown 

 in the diagrammatic re- 

 presentation (Fig. 170). I 

 shall now proceed to des- 

 cribe the mechanical res- 

 ponse induced by unilateral 

 stimulation of the root tip* 

 As the responding region 

 of growth is at some dis- 

 tance from the tip, the stimulation is therefore indirect. 



Experiment 180. — I employed at first mechanical stimu- 

 lus of moderate intensity by rubbing one side of the tip of 

 the root of Bindweed ; this induced a movement away from 

 stimulus. Unilateral application of dilute acid gave rise 

 to a similar response. Thermal stimulus of moderate intensity 

 also induced responsive movement away from the stimulus 

 (Fig. 171). 



Fit;. 170. — Mechanical and electrical 

 ie.=ponse to indirect stimulation at dotted 

 arrow. In figure to the lett, the point 

 A, on the same side undergoes expansion- 

 >vith responsive mechanical movement 

 away from stimulus indicated by con- 

 tinuous arrow. In figure to the right, 

 indirect stimulus at dotted arrow induces 

 electric response of galvanometric posi- 

 tivitj- at A, indicative of increase of tur- 

 gor and expansion. 



