462 LIFE MOVEMENTS IN PLANTS 



(4) The Electrical response to Indirect unilateral sti- 

 mulus. 



MECHANICAL RESPONSE TO DIRECT STIMULUS. 



As the geotropic responses of the shoot and the root are 

 opposed to each other, the object of the investigation is to 

 find out ; whether the response of the root to various stimuli 

 is specifically different from that of the shoot. We have 

 seen that tissues in" general respond to direct unilateral 

 stimulus by contraction of the proximal and expansion of 

 the distal side, the tropic curvature being thus positive. We 

 shall now determine whether direct unilateral stimulation 

 of the root induces a tropic movement which is similar or 

 dissimilar to that exhibited by the shoot. 



Experiment 178. — In experimenting with roots of vari- 

 ous plants I obtained results which are precisely similar 

 to that of the shoot. The movement of the root was ob- 

 served by means of a reading microscope focussed on the 

 tip of the organ. I employed various forms of stimuli, me- 

 chanical, thermal, and chemical. Unilateral application of 

 these on one side of the growing region gave rise to a posi- 

 tive tropic curvature, resulting in a movement towards the 

 stimulus. These experiments confirm Sachs' observation 

 that unilateral application of stimulus in the region of 

 growth induces positive curvature of the root. 



ELECTRICAL RESPONSE TO DIRECT STIMULATION. 

 I next undertook an investigation on the electric response 

 of the root to direct unilateral stimulation. 



Experiment 179. — The terminals of the galvanometer 

 were suitably connected with the two diametricaliy opposite 

 points A and B in the growing region of the root. Stimulus 

 was now applied very near the point A, the various stimuli 

 employed in different experiments being : (1) mechanical, 

 {2) chemical, and Q\) thermal. In every instance the excited 



