4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 92 



It will be seen from this table that the amount of energy which 

 barely causes phototropic curvature varies with the wave length. The 

 yellow (5700 A) is about 600 times as intense as is the white light 

 necessary to bring about the same response, while the green (5460 A) 

 is approximately 400 times as intense, and the blue (4360 A) only 

 .03 as strong as the energy of his standard white light. The blue is 

 thus approximately 10,000 times as efifective phototropically as the 

 green and 20,000 times that of the yellow. The violet (4050 A) is 

 also very efifective but only about half that of the blue. 



350 



Fig. I. — Graphs from Bachmann and Bergann showing the sensitivity of Avena 

 sativa to wave lengths of light (continuous line) compared with their cor- 

 rected values of Blaauw (crosses), of Sonne (circles), and of Koningsberger 

 (horizontal lines). 



Bergann (1930) made a very careful study of the effects of mono- 

 chromatic light on the growth and bending of Az'cna sativa as well as 

 the effects produced by a change of intensity and length of exposure. 

 Employing the method of placing the young plant between two oppos- 

 ing lights, he concludes that the regions other than the red and infra- 

 red produce corresponding growth reactions for suitable intensities. 

 In unilateral light equal bending is shown for corresponding intensi- 

 ties, first positive, then negative, and finally positive. Light curvatures 

 and light-growth reactions are parallel processes. The stronger the 

 light-growth reaction in a given wave-length region, the greater will 

 be the phototropic response. The seedlings " choice " in the com- 

 pensation experiments between two wave-length ranges is always that 

 which corresponds to the stronger growth reaction. 



