38 GERLOFF, FITZGERALD, AND SKOOG 



ment were harvested after seven days of grov^th and the remaining 

 two after twelve days to avoid any error that might result if cul- 

 tures containing suboptimal concentrations of nitrate reached 

 maximum growth in a relatively short time, then decreased in dry 

 weight before the cultures with higher nitrate concentrations had 

 reached their maxima. Such decreases in weight did not occur, 

 however, for in cultures D through H where growth was limited 

 by low nitrate and reached a maximum in seven days, the dry 

 weights did not decrease during the next five days. 



The dry weight determinations after twelve days of growth 

 show that for maximum yields of Coccochloris Peniocystis 

 the nutrient solution must contain a relatively high concentra- 

 tion of nitrate. The 5.7 mg. increase in dry weight produced by 

 Treatment A over Treatment B is probably not significant. How- 

 ever, the 13.5 mg. difference between Treatments A and C is sig- 

 nificant, so that at least 13.6 ppm. of nitrogen are necessary for 

 maximum growth of this organism under the conditions of this 

 experiment. This was substantiated by the appearance of the cul- 

 tures at the twelve-day harvest, for those of Treatments A and B 

 were still a dark blue-green color while cultures of Treatment C 

 had turned a yellowish-green. Furthermore, chemical tests showed 

 that nitrate was completely absent from cultures of Treatments 

 B and C, yet approximately 6.0 ppm. of nitrate nitrogen remained 

 in the cultures of Treatment A. 



Table 4 also shows the pH of the culture solutions at the 

 twelve-day harvest. In this and other experiments, the pH of the 

 culture solutions was approximately 8.0 when inoculated, and 

 in the solutions with the heaviest growths it gradually increased 

 to 10.5 and ii.o after twelve to fourteen days. From the results 

 of the pH experiment, this alkaline shift would seem to be highly 

 desirable. It was probably due to removal by the algae of bicar- 

 bonate ions present in the equilibrium mixture produced by 

 Na2C03 in the culture solution and CO2 from the atmosphere 

 as well as to rapid utilization of the nitrate ion. 



Table 5 presents the results of additional experiments on the 

 effects of varying individually the concentrations of phosphorus, 

 sulfur, potassium, calcium, magnesium, and iron on the growth 



