108 



1>. LATIMEK, T. T. BANNISTER, E. I. RABINO WITCH 



and Norris (7). The phycobilin pigments were kept at about 5°C. 

 during the purification and the fluorescence measurements. Fluores- 

 cein (Eastman, Reagent Grade) was used without further purification. 

 The algal cells, upon remov^al from the culture line, were sus- 

 pended in carbonate buffer #9 and exposed for V2 to 2 hours to visible 

 white light, with an intensity of about 3000 ergs/ (cm. ^ sec.) (^-100 

 lux). Less than 30 seconds elapsed between the removal of the cells 

 from this light and the measurements — a procedure which eliminated 

 well known transients in the intensity of fluorescence following a dark 

 period. The temperature of the live cells and of pigments other than 

 phycobilins was about 25°C. Prof. Robert Emerson and Mrs. Ruth V. 



Golvonometer 



Photomulliplier tube (RCA 6217) 



Filter opaque to exciting light 



Baffle 



Vessel containing 

 Fluorescing material 



White matt surface-* 

 ^Grating Monochromotor Fluorescence' 



{ Bausch and Lomb) 



Ulbricht or Integrating Sphere 



Fig. 1. Arrangement of apparatus for measuring fluorescence. 



Chalmers* grew the algal cells and determined the light intensities 

 corresponding to compensation and to one-half saturation of photo- 

 synthesis. DilTerent cells were used in the studies of fluorescence and 

 photosynthesis, but they were of the same strain and identically 

 cultured. 



The light intensities were measured by means of a photomultiplier 

 tube (RCA 6217): The spectral sensitivity curve of the detector sys- 

 tem was determined with a bolometer. By measuring the response 

 of the tube to monochromatic light projected into the sphere, rather 

 than to light falling directly on the tube, we obtained a calibration 

 which accounted not only for the selective sensitivity of the tube but 

 also for changes in the reflectivity of the sphere walls with wave- 

 length. The apparatus is shown in Fig. 1. 



As an indirect check of this calibration, we measured the fluores- 



Working on Xiitional Science Foundation Contract G-Ky!)S. 



