CHLOROPHYLL FORMATION 



413 



leaves perceptibly, and Issatschenko (1907) claimed that chlorophyll is 

 formed in bacterial light. 



There is evidently a threshold light intensity below which protochloro- 

 phyll is not transformed to chlorophyll. Lubimenko (1928) found that 

 etiolated barley plants illuminated for 10 hr with relative light intensities 

 of 100, 11.1, and 6.25 formed relative quantities of chlorophyll of 100, 

 21, and 0. These data demonstrate that a threshold intensity exists for 

 chlorophyll formation. 



At relatively low light intensities the rate of formation of chlorophyll 

 is directly proportional to the light intensity (Wiesner, 1877; Schmidt, 





10 20 30 



TIME ILLUMINATED, 



40 



hr 



50 



10 



20 30 40 50 60 

 TIME ILLUMINATED, hr 



Fig. 7-12. Changes brought about in 

 the content of total ether-soluble mag- 

 nesium and chlorophyll magnesium by 

 illumination of dark-grown barley leaves 

 at 7°C. {Stnith, 1949a.) 



Fig. 7-13. Changes brought about in 

 the content of total ether-soluble mag- 

 nesium and chlorophyll magnesium by 

 illumination of dark-grown barley leaves 

 at 19°C. iS)nUh, 1949a.) 



1914; Greilach, 1904; Liro, 1908; Koski and Smith, 1948-1949; Koski, 

 1949). 



This was convincingly demonstrated by Liro (1908), who investigated 

 the transformation of protochlorophyll ("leukophyll") to chlorophyll in 

 two ways: by measuring the time necessary to form the first spectro- 

 scopically detectable trace of chlorophyll at different distances from a 

 given light source, and by measuring the dilution necessary to cause the 

 disappearance of the chlorophyll band produced by a constant time of 

 illumination with a given weak light source at different distances. From 

 Liro's results it is evident that the rate of formation of the first trace of 

 chlorophyll is proportional to the Hght intensity as measured by the 

 inverse-square law. 



