316 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1934 



+ + 



T4 1 VA '2 



Figure 1. — Graphs from Dillewijn showing growth of Avena sativa. Abscissa represents 

 time in hours and the ordinate rate of growth in n per minute. The intensity of 

 light is indicated in meter-candles. The light line represents the growth response for 

 1/30 the light intensity of that bringing about the response shown by the heavy line. 

 The arrow indicates the moment of illumination with the duration marked above. The 

 predicted phototropic response is indicated by plus and minus signs. 



