SUMMARY 115 



plants it is only about 30 seconds instead of minutes. The 

 latent period is shortened under increased intensity of 

 light. 



The shortest period of exposure necessary to induce 

 responsive contraction under the action of light is extremely 

 short in certain cases. The seedling of Wheat responded 

 to a flash of light from an electric spark, the duration of 

 which is about a hundred thousandth part of a second. 



Tropic curvature increases with the intensity and dura- 

 tion of exposure to light. It also increases with the directive 

 angle, the effect being approximately proportional to sin 0, 

 where is the angle made by the rays with the surface of 

 the responding organ. 



Within the median range of stimulation the intensity 

 of induced tropic effect is proportional to the quantity of 

 incident light. 



