CHLOROPHYLL FORMATION 



395 



A similar set of curves for ether extracts of barley seedlings is shown in 

 Fig. 7-2. The leaves had been illuminated for periods of 0, 2, 24, 47, 

 and 71 hr before extraction. In the extract of the unilluminated leaves 

 the strong absorption of the carotenoids beyond 480 m^ and of proto- 

 chlorophyll at 625 m^ (see inset) is apparent. Illumination of the leaves 



400 



500 600 



WAVE LEMGTH, mfl 



700 



Fig. 7-2. Absorption coefficients of ether extracts of 50 g of barley leaves greened for 

 different periods of time. (Smith, 1947.) 



for 2 hr produces enough chlorophyll to be discernible in the extracts 

 (see also in the inset) and causes the disappearance of the protochloro- 

 phyll spectrum. Longer illumination periods, up to 47 hr, increase the 

 chlorophyll content greatly. Further illumination, however, produces no 

 additional chlorophyll. The cessation of chlorophyll accumulation after 



