142 CHAP. XIII. DIA-PHOTOTROPISM 



Since the responding growing region is at some distance 

 from the tip, the stimulation of the root was indirect in this 

 experiment. The negative curvature of the root in response 

 to indirect stimulation is by no means unique, for a similar 

 effect is induced by indirect stimulation of the shoot, as 

 shown in the following experiment. 



Effect of Indirect Unilateral Stimulation 



OF Shoot 



Experiment Sy. — I took a young shoot of Vicia Faba, 

 and after finding its region of maximum growth, applied 

 unilateral light at a distance of 5 cm. below that region, the 



Fig. 80. Negative response of shoot under indirect 

 unilateral photic stimulation (Vicia Faba). 



moment of application being indicated by the vertical 

 arrow in the record. The stimulation was, therefore, 

 indirect. Light is seen to have induced negative curvature, 

 shown by the down-curve, which persisted for a while 

 after the cessation of light marked by the horizontal arrow 

 within the circle. There was a subsequent recovery which 

 was complete (fig. 80). 



I have obtained a similar negative response on the 



