96 Marine Microbiology 



"F" (Table 1) in 125 ml Erleiimeyer flasks. The basic enrich- 

 ment for the experiments was 'F' with nitrate omitted. Experi- 

 mental flasks were washed with detergent and soaked in 30 

 per cent HCl. All but three species of the algae were grown 

 under 4000 - 10,000 meter-candles of light provided by equal 

 numbers of "cool-white," "natural," and "daylight" fluorescent 

 bulbs at 20 - 22 C. Three species required the temperatures in- 

 dicated and were provided ca 8000 meter-candles' illumination 

 from "cool-white" bulbs: Detomila confervacea, 4 to 8 C; Tlui- 

 lassiosira nordenskioldii 8 to 12 C; Rhizosolenia setigera, 15 C. 

 The buffer tris ( hydroxymethyl ) amino methane, (500 mg/L, 

 pH 7.2) was added to the medium for these three species; it 

 did not serve as a nitrogen source. 



The sea water used for all experiments was collected from 

 the Sargasso Sea and aged for several months. It contained the 

 following ( before enrichment ) : 



NO2 + NOj-nitrogen 0.82 ^M 



ammonia nitrogen 2 /iM 



Methods of analysis are cited by Ketchum et ah (14). 



Inoculum was taken either from dense stock cultures suitably 

 diluted with sea water or from cultures prepared without added 

 nitrogen to deplete the cells. The number of cells transferred 

 varied from as few as 10/ml to ca 5000/ml. Yields of all algae 

 except Melosira sp. were measured by counting cells in a hemo- 

 cytometer, Palmer-Mahoney chamber, or Sedgwick-Rafter cham- 

 ber, as appropriate. Melosira filaments were separated in a tissue 

 homogenizer and optical densities of cultures compared in a 

 spectrophotometer at 750 m/x. Cell numbers were assumed pro- 

 portional to optical density. 



Replication was provided by repeating the assay for each 

 organism rather than by having replicate flasks in any one experi- 

 ment. Thus each repetition of the experiment received inoculum 

 from a different culture, and soinetimes had a different light in- 

 tensity. 



Nitrate and glycine were autoclaved in the medium in some 

 experiments but usually N-sources were sterilized separately and 



