C. STACY FRENCH 



63 



impossible to use such curves to substantiate the existence of other 

 pigments with long-wavelength fluorescence bands, although that 

 would be the more obvious conclusion to be drawn from them. Virgin 

 (1954) has found that the distortion of fluorescence spectra is very 

 strongly influenced by the degree of light scattering within the leaf. 

 This distortion can be greatly reduced by infiltrating the air spaces of 

 the leaf with water. 



S4iu iaddcflt 



436111^ iMidtst 



600 



650 700 



WAVELENGTH 



750 BA 



Fig. 12. Fluorescence spectrum of a dark green leaf, Photinia arbutifolia, when 

 illuminated by strongly absorbed blue light as compared with weakly ab- 

 sorbed green light. ( Hill, Young, and French, unpublished. ) 



Protochlorophyll 



The fluorescence spectrum of purified protochlorophyll in acetone 

 is illustrated in Fig. 13. The fluorescence spectrum of something 

 which might be called a chloroplast preparation from etiolated barley 

 is also given. This curve bothered us greatly for some time, because 

 the measurements of the action spectrum for the transformation of 

 protochlorophyll to chlorophyll (Koski, French, and Smith, 1951) 



