l8o CHAP. XVI. RADIO-THERMOTROPISM 



positive curvature, after which the movement became 

 arrested by the arrival of the excitatory impulse at the 



Fig. 105. Record of positive, neutral, and negative curvature 

 under continued unilateral action of thermal radiation. 

 The negative response went off the plate. Successive dots 

 at intervals of 5 seconds. (Dregea volubilis.) 



distal side, on account of which the positive curvature be- 

 came neutrahsed. Further continuation of the stimulation 

 caused a reversal into negative in the course of 7 minutes. 



Negative Thermotropism 



Experiment 109. — The response does not stop at 

 neutralisation but proceeds further, ending in reversal ; 

 that is, to pronounced negative curvature by the contraction 

 of the distal side due to conduction of excitation, and to 



