REQUIREMENTS FOR THE MAINTENANCE AND GROWTH OF APHANIZOMENON FLOS‐AQUAE IN CULTURE 1, 2

SUMMARY Aphanizomenon flos‐aquae has been introduced into unialgal culture in a completely defined medium and maintained for more than 3 years in the colonial flake form found in nature. The color and size of the flake and general appearance of the cells are substantially improved over those found in the original material at the time of collection from Upper Klamath Lake, Klamath County, Oregon. The alga readily forms both akinetes and heterocysts in culture Bacteria‐free cultures have not been obtained. A precipitate‐free medium designated ASM No. 8a has been developed from the ASM of McLachlan and Gorham. Their medium was altered by modifying the concentration of certain elements and by the addition of sodium bicarbonate, a 1/25 dilution of Arnon's trace element solutions B 7 and C 13 , hydrogen ferric ethylenediamine di ‐o‐ hydroxyphenylacetate (EDDHA), and disodium ethylene dinitrilotetra‐acetate (Na 2 EDTA).