60 



FLUORESCENCE SPECTROPHOTOMETRY 



pink. The fluorescence spectrum of the blue fraction when illuminated 

 by two different incident wavelengths is shown in Fig. 8. Now it is 

 ordinarily found that a pure substance illuminated with different 

 wavelengths gives the same fluorescence spectrum, but this prepara- 

 tion gives different spectra for the two incident wavelengths. It is 

 clear that the material fluorescing at 687 m/x absorbs at 436 m/A more 

 strongly than it does at 405 m^u., since 436 m/x excites the 687-m;u, band 



600 



6S0 700 



WAVELENGTH 



7S0ni^ 



Fig. 10. Fluorescence spectrum of a thin layer of a live green plant as compared 

 with an ether solution of chlorophyll a. (Smith, unpublished.) 



more than it does the near infrared fluorescence, whereas 405-m/A 

 incident light does the reverse. The green fraction, Fig. 9, of the bac- 

 teriochlorophyll preparation, however, shows only the 687-m/x fluores- 

 cence band. This green pigment appears to be very simflar to bacterio- 

 viridin of the green photosynthetic bacteria, and it may be normally 

 a minor constituent of purple bacteria or may be a decomposition 

 product formed during extraction. 



