a. B.C. D, 



"^ 



z. 



5, 



FIG. 22. Effect of spectral colours on starch production 



Hydrangea leaves, still attached to the plant, have been deprived of starch by keeping in 

 the dark. They have then projected upon them a small solar spectrum for five to six hours 

 Subsequent treatment with iodine, in the usual way, shows a picture of the absorption 

 spectrum of chlorophyll in the blue " compound " of iodine and starch. The lower piece of 

 leaf has been partially covered with a screen, represented below it, in such a way that the 

 wider part of the aperture corresponded with the region of the spectrum between the lines 

 B and C. 



(From " Proc. Roy. Soc.," Timiriazeff.} 



