318 



LIFE MOVEMENTS IN PLANTS 



depends on the intensity and duration of the incident 

 light. A moderate and effective stimulation may thus be 

 produced by short exposure to strong light. For my 



Fig. iiii. 



Fm. 114. 



Fig. 113. — Positive curvature under moderate phototropic stimulation. Note 

 complete recovery {Drepea). 



Fig. 114. — Pe-sistent positive curvature under stronger stimulation {Dregea). 



present experiment I toolc a stem of Dregea volubilis, and 

 applied light from a small arc lamp to one side of the 

 organ for 1 minute ; this induced a positive curvature 

 followed by complete recovery on the cessation of light 

 (Fig. 113). 



Effect of strong stimulation : Experiment 119. — After 

 recovery of the stem of the last experiment, the same 

 light was applied for 5 minutes. It is seen that the 

 curvature is greatly increased (Fig. 114). Thus the photo- 

 tropic curvature increases, within limits, with the duration 

 of stimulation. The curvature induced under stronger 



