LIGHT AND VEGETATION 87 



been the subject of numerous experiments. The formation of 

 auxins and their movements in the plant are directly dependent 

 on light, and the wave-lengths of the active radiations and of 

 those to v^hich the plant is indiflferent are known. 



Other examples could be taken from the chapter on 

 photoperiodism. 



This collection of more or less well-known facts reveals 

 an infinitely small part of the chemical processes which we 

 have to conjecture in order to interpret a large number of 

 observations. 



