414 



LIFE MOVEMENTS IJf PLANTS 



at the distal side. This latter effect is, as we have seen, 

 brought about by the effect of indirect stimulation. 



But under long continued action of stimulus, the nega- 

 tive or excitatory impulse reaches the distal side, inducing 

 diminution of turgor and retardation of the rate of growth. 

 This leads to neutralisation, the organ placing itself at 

 right angles to the orienting stimulus. 



Experiment 75S.— This neutralisation is seen in the 



Fig. 152.— Record of positive, neutral and reversed negative curvature under 

 continued action of thermal radiation. The negative response went off the plate. 

 Successive dots at intervals of 5 seconds. {Dregea volnhilis). 



record given in figure 152, where under continuous uni- 

 lateral stimulation, the growing organ exhibited its maxi- 

 mum positive curvature, after which the movement became 



