6l8 PLANT RESPONSE 



case of light. It is seen in the return of the organ to its 

 original position, or by oscillations about that position as the 

 mean ; but in cases where the proximal becomes fatigued, 

 the responsive contraction of the distal gives rise to a nega- 

 tive curvature. In all these cases we see thermal radiation 

 inducing the same curvature effects — positive, neutral, and 

 negative — as were found to be induced by visible light. 



Effect of electric waves on growth. — I shall next describe 

 the effect of Hertzian waves in inducing responsive curvatures ; 

 and first, in order to obtain the fundamental effect on growth 

 itself, I took an electric radiator consisting of a rod 5 cm. 



Fig. 250. Effect of P^lectric Waves on Growth 



Connection with electric vibrator at downward arrow (|) is seen to arrest 

 growth and to induce contraction, by which the specimen undergoes 

 an actual shortening. 



in length, excited by oscillatory discharge from a Ruhmkorff's 

 coil. The specimen was a flower-bud of Crinum Lily, whose 

 upper and lower ends were connected by means of thin wires 

 with the two ends of the electric radiator. The natural 

 growth-record under unbalanced conditions was first taken 

 (fig. 250), and the specimen was now subjected to the action 

 of electric waves at the point marked in the record with a 

 downward arrow. It will be seen that this gradually 

 diminished the rate of growth, till at the end of five minutes 

 it was completely arrested ; and as the action of the electric 

 waves continued, the contractile effect by which growth is 

 arrested is seen to be carried further, actually bringing about 

 a shortening in the length of the specimen. 



