i6o 



CHAP. XV. PHOTONASTIC PHENOMENA 



downwards or upwards by a totally reflecting prism 

 (fig. 88). The two devices just described ensure accurate 



Fig. 88. Arc-lamp with totally reflecting prism for application 

 of strong light vertically downwards or upwards. 



investigation of the effects of local application of feeble or 

 strong light on the upper and lower halves of the organ. 



Effect of Light on Upper Half of the 



pulvinus 



Experiment 93. Effect of feeble or moderate intensity 

 of light. — The record, with moderate magnification, w^as 



Fig. 89. Records of effect of feeble light (left illustration) and 

 of strong light (illustration to right) on upper half of pulvinus 

 (Mimosa). Successive dots at intervals of i second. In this 

 and in the following records up-movement is represented by 

 down- curve and vice versa. 



taken on a fast-moving plate, the successive dots being 

 at intervals of a second. The record to the left (fig. 89) 



