PHOTOTROPIC RECORDER 



103 



bearings has a small wheel (smaller than represented in the 

 figure) to which is attached the leaf (upper figure) or the 

 stem (lower figure). The up-movement of the leaf under 



Fig. 50. The Phototropic Recorder : for pulvinated organ 

 (upper figure), for growing organ (lower figure). 



vertical Hght, or the bending of the stem in response to 

 unilateral photic stimulation, is recorded as an up-curve 

 on an oscillating smoked-glass plate. 



Positive Phototropic Response of Pulvinated 



Organs 



Experiment 59. Response of pulvinated organs. — For 

 this experiment I employed the terminal leaflet of Phaseolus. 

 The source of illumination was a 32-candle-power electric 

 lamp, enclosed in a metallic tube with a circular aperture for 

 passage of the light. The leaflet was attached to the Photo- 

 tropic Recorder. Light was applied on the upper surface of 

 the pulvinus for 20 seconds ; this induced an up-movement 

 of the leaflet, due to the contraction of the upper half of the 



