GBO-BLECTRIC RESPONSE OF SHOOT 



455 



in boiling water, the plant gave no electric response lo 

 geotropic stimulus. 



EFFECT OF DIFFERENTIAL EXCITABILITY OF THE ORfiAN. 



I have hitherto <lescril)ed the geo-electric effect of 

 radial and isotropic organs. The induced E. M. F. at 90° 

 was found practically the same whether A was above and 

 B below, and uice versa. In the mechanical response of the 

 pulvinus of Mimosa, the geotropic excitability was, however, 

 found to be greater in the lower half than in the upper 

 (p. 440). I wished to investigate the question of differential 

 geotropic excitability anew, by means of electric response. 



Experiment 175. — Electric connections with the galvano- 

 meter were made with the upper and lower halves of the 

 pulvinus, the organ being placed in the vertical or neutral 

 position. The angle of inclination was then increased to 

 90° in the positive and negative directions alternately. 



TABLE XXXIV. — DIFFERENCE OF GBO-ELECTKIC RESPONSE OF UPPER AND 

 LOWER HALVES OF THE PL'LVINUS OF Mimosa. 



In the former case the upper half of the pulvinus occu- 

 pied the up-position ; in the second case the up-position was 

 occupied by the lower half of the pulvinus. In both cases 

 strong electric responses were obtained, the upper point 

 of contact being always galvanometrically negative. There 

 was, however, a difference between the two responses, the 

 excitatory electro-motive variation was invariably greater 



34 



