INDIRECT STIMULATION 



177 



that is, indirect stimulation, has been shown to induce a 

 negative curvature away from the stimulus ; when the 

 effective stimulation was made stronger, a diphasic response 

 occurred, a negative followed by positive [cf. fig. 63). 



Experiment 104. — A parallel experiment was carried 

 out with the stem of a seedling of Vicia Faha. Application 

 of unilateral thermal stimulation at a distance of 6 cm. 

 below the region of maximum growth evoked a negative 

 response, curvature away from the stimulus indicating 



Fig. 1 01. Fig. 102. 



Fig. ioi. Effect of indirect radio-thermal stimulation. 



Duration of application of stimulus between vertical line and 

 horizontal arrow within circ'e. Negative response followed 

 bv complete recovery. (Vicia Faba.) 



Fig. 102. Diphasic response of identical specimen under more 

 effective stimulation. Negative response followed by 

 positive. (Vicia Faba.) 



acceleration of growth on the same side. This is seen in 

 the record (fig. loi) ; thermal radiation was applied at the 

 vertical line and withdrawn at the horizontal arrow in 

 a circle, the total duration of stimulation being 40 seconds. 

 The down-record represents negative curvature ; the move- 

 ment persisted for a further period of 40 seconds, after 

 which there was complete recovery. 



N 



