461 



S. S. Brody and M. Brody 



II. MATERIALS AND METHODS 



A schematic diagram of the photofluorometric apparatus we use is shown 

 in Fig. 2. Uncorrected spectra are recorded graphically, and simultaneously 



Chopper 



Fig. 2 Schematic diagram of spectrofluorometer : Xe = 1800 watt high press- 

 ure xenon arc lamp; L = lens; Mj = monochromator for sensitizing fluores - 

 cence; M - mirrors; S - sample; D. = Dewar; L = light pipe; Pj = Photo- 

 multiplier tube for measuring absorption; M2 = monochromator for analyzing 

 fluorescence; P2 = photomultiplier tube for measuring fluorescence; C = 

 commutator for triggering frequency counter and card punch. 



corresponding values are punched onto IBM cards at 2 nn|j. intervals. The 

 spectral response of the apparatus is calibrated by using a standard lamp, 

 according to the method described by Stair, Johnston and Halboch (51). The 

 intensity of the light incident on the sample is determined with a thermopile. 

 These calibrations are incorporated into a computer program which (among 

 other things) corrects all fluorescence and excitation spectra and plots the 

 corrected curves. Thus, unless otherwise indicated, all spectra have been 

 corrected on a quantum basis. 



To deplete Euglena gracilis (Z) of its chlorophyll, the organism is cultured 

 in total darkness for over 20 generations. In the present work, the term 

 "age of the organism" will refer to the period of time of subsequent culturing 

 in light. 



III. RESULTS AND DISCUSSION 



A. Photochemical Activity and Morphology of Cells which were Frozen 

 and Thawed 



Since many of the observations of fluorescence of algae are made with 

 organians subjected to extremely low temperatures, it was deemed desirable 



