somewhat synchronous in respect to cell division. If this is true, and 



the cell weight increase is constant throughout the growth period then 



weight increase would be greater in respect to uptake during the early 



phase of cell growth. This would account for some of the observed difference 



in uptake rate. 



The same procedure was used for the study of the accumulation of 



Cs-Ba ' by N. seriata as was used with G. simplex except the samples 



were withdrawn at 24, 56 and at 72 hours. The rate of uptake of the 



Cs-Ba isotope by N. seriata was extremely low, but did show a gradual 



increase over the 7 2-hour period. The results of the counts together 



with the concentration factors are tabulated in table 8. 



Table 8 . The accumulation rate of Cs-Bal37 by N. seriata 

 (medium: 10.2 x 10^ cpm/ml) 



These results are similar to those obtained by Williams and Swanson (1958), 

 They found that when Chlorella was grown in a medium which contained stable 

 cesium, the concentration factor was approximately unity. They also found 

 that the amount of potassium in the medium had an effect on the concentration 

 of cesium accumulated by the organisms. They indicated that cesium and 

 potassium formed a pool and that potassium in the medium depressed the 



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