ISOLATION, PURIFICATION, NUTRITION 43 



solutions of known composition states, "It seems that Gloeotrichia 

 requires for its growth access to one or several organic substances 

 which are not thermostable." Also, Pringsheim (1946) found 

 that soil-and-water cultures as well as various extracts and organic 

 materials were useful for culturing many algae. Even in the early 

 work on the present project, when the first attempts to culture 

 some species, including Microsystis aeruginosa Kiitz. Elenkin 

 and Gloeotrichia echinulata (}. E. Smith) Richter, were unsuc- 

 cessful, it was thought that the nutrient medium perhaps lacked 

 some essential organic constituents, and extracts of leaf-mould, 

 soil, and other organic materials were added to the culture solu- 

 tions. The extracts never meant the difference, however, between 

 growth and no growth. They did influence the rate of growth to 

 a slight extent, but not to a greater degree than could be dupli- 

 cated by modifications of the inorganic solutions. The difficulties 

 encountered in culturing some species apparendy were due to an 

 unsatisfactory physiological condition of the algae obtained in 

 the first lake water samples, for, in all cases, persistent sampling 

 of different parts of the lakes provided cells that grew satisfac- 

 torily in inorganic media. It may be that further investigations 

 will reveal organic substances which will stimulate growth be- 

 yond that produced in inorganic solutions. The fact that twenty- 

 four species of blue-green algae are in continuous culture in one 

 inorganic solution, however, strongly indicates that as a group 

 they do not require organic substances or unknown factors for 

 normal growth. 



The mineral nutrition experiments with Coccochloris Penio- 

 cystis (Kiitz.) Drouet and Daily show the relative amounts of 

 the major essential elements required for maximum growth and 

 illustrate a method by which quantitative information on the 

 nutrition of other blue-green algae may be obtained quite easily 

 once the organisms are obtained in pure culture so that they can 

 be grown under controlled conditions. From a practical stand- 

 point, probably the most important result from these experi- 

 ments was that this organism requires such a high level (13.6 

 ppm.) of nitrate nitrogen as compared to phosphorus (0.45 

 ppm.) to produce maximum growth. If bloom-producing species 



