42 GERLOFF, FITZGERALD, AND SKOOG 



be used indefinitely as an iron source for algal culture. In fact, 

 the old ferric chloride solution was inhibitory at high concentra- 

 tions, for growth increased as the iron concentration in the cul- 

 ture solution was reduced. This effect may have been caused by 

 gradual conversion of the iron to Fe203 which when added to 

 the culture solution precipitated tlie phosphate in an unavailable 

 form. 



Table 6 — Comparison of ferric citrate and ferric chloride as a source of 

 iron for Coccochlaris Peniocystis. Cultures inoculated on Dec. 3, 

 1949 and harvested Dec. 16, 1949. 



Oven-dry weight of algae (mg.) in 400 ml. solution 



Ferric citrate 



solution Ferric chloride solution 



Concentration 



of Fe 3 days old 3 days old 20 months old 



1,12 ppm 105.5 105 7 47.9 



0.56 ppm 114.7 111.1 44 1 



0.14 ppm 109.5 99.1 48.0 



0.06 ppm 115.2 • ■ 81.2 70.6 



0.03 ppm 108.1 75 70 4 



Discussion 



The results presented in this paper show that many species 

 of blue-green algae, including the bloom-producers. Microcys- 

 tis aeruginosa Kiitz. Elenkin, Gloeotrichia echinulata (J. E. 

 Smidi) Richter, and Aphanizomenon fios-aquae (L.) Ralfs, can 

 be cultured continuously in inorganic solutions of completely 

 known composition. This is significant in view of the references 

 in the literature to the possible importance of organic substances 

 for the growth and successful culturing of blue-green algae 

 (Hutchinson, 1944), (Pearsall, 1932), (Rodhe, 1948). As a speci- 

 fic example, Rodhe (I.e.), who obtained some growth of Gloeo- 

 trichia in a culture of soil and lake water, but no growth after 

 the soil and water had been heated, and no growth in nutrient 



