368 LIFE MOVEMENTS IN PLANTS 



the stimulus of light. The experiment was carried out 

 in a dark room, special precaution being taken that light 

 was screened off from the plant except at points of 

 localised stimulation. 



EFFECT OF LIGHT AT THE TIP OF THE ORGAN. 



Experiment 137. — If the tip of the seedling of Setaria 

 be illuminated on one side, it is found that a positive 

 curvature {i.e., towards light) is induced in the course 

 of an hour or more. But in obtaining record of the 

 seedling by unilateral stimulation of the tip, I found that 

 the immediate response was not towards, but away 

 from light (negative curvature). The latent period was 



Fig. 136.— Response of seedling of Setaria to unilateral stimulation of the tip 

 applied at dotted arrow. 



Note preliminary nesrative curvature reversed later into positive. 



about IJO seconds and the negative movement continued 

 to increase for 25 minutes (Fig. 13G). This result, hitherto 



