500 LIFE MOVEMENTS IN PLANTS 



excitability. On the first occasion referred to, thunderstorm 

 held broken out at night, and it was refreshingly cool 

 in the morning. It was with the utmost surprise that I 

 noted the astonishing violence of the geo-electric response 

 which the plants gave that morning ; the maximum res- 

 ponse hitherto obtained was about 100 divisions of the 

 galvanomter scale ; but on the present occasion the displace- 

 ment of the plant, from vertical to horizontal position, 

 induced responsive deflection so great that the galvanometer 

 spot of light flew off the scale of 3,000 divisions, I was 

 at first incredulous of the results and wasted the valuable 

 occasion in trying to discover some hidden source of error. 

 Subsequent tests showed that my misgivings were groundless, 

 and that the extraordinary large deflection was really due 

 to geo-electric reaction. On the second favourable occasion, 

 which lasted for three hours (during the cool hours of 

 the morning), I was able to secure a number of important 

 observations. Thus displacement of the flower stalk of 

 Nyinplicpa through 4-90^ was immediately followed by 

 gBO-electric response, the deflection being about 3,000 

 divisions of the scale. The latent period hardly exceeded 

 a second ; the return of the plant to the vertical position was 

 quickly followed by electric recovery which was complete. 

 The above results were obtained with the same specimen 

 time after time without a single failure. The successive 

 responses showed no sign of fatigue. Another remarkable 

 ett'ect was noticed during gradual increase of the angle of 

 inclination. Nothing happened till a critical angle was 

 reached, which was roughly estimated to be about 33°; 

 when this critical angle was exceeded by a single degree, 

 there was a sudden precipitation of geo-electric response. 

 The experiments were repeated time after time with the 

 identical result. It appeared as if some frictional resis- 

 tance obstructed the displacement of the geotropic particles 

 accumulated at the basal end of the cell, and it was not 



