463 



S. S. Brody and M. Brody 



2 6 10 14 la 22 2S M 



TIME, MINUTES 



Fig. 3 Hill reaction of whole Chlorella cells. Control (closed circles) 

 to be compared to cells which have been frozen and thawed (open circles). 



3. State of Chlorophyll Aggregation : Comparison of "control" algal cells 

 (Euglena, Chlorella ) with those that had been frozen and thawed, revealed 

 no appreciable change in absorption properties. Furthermore, the emission 

 spectrum, the excitation spectrum, and the fluorescence yield remain charact- 

 ertistic for each temperature during the course of two to three cycles of 

 freezing and thawing. However, after repeated cycles (five to six) a small 

 shift in emission spectrum and diminution of intensity of fluorescence do 

 occur. We feel that there is no evidence at the present time to indicate that 

 a single rapid freezing of cells results in disruption of the normal distribution 

 of monomeric and aggregated chlorophyll. 



B. Emission from the Aggregated State in Vivo 



(In this section^ the wavelengths^ given are not corrected for the spectral 

 response of the apparatus. ) 



When young (Z day old) pale-green cells of Chlorella pyrenoidosa are 

 excited with the 436 mjx Hg line, at room temperature, the resulting fluore- 

 scence spectrum consists of a main band with maximum at 685 m\x and a 

 secondary band at about 720 m|i.. (The latter represents a mirror image of 

 the first vibrational band in the absorption spectrum of chlorophyll a. ) 

 (See Fig. 4) Excitation of young, pale-green cells of Euglena gracilis results 

 in a similar emission spectrum. 



