ISOLATION, PURIFICATION, NUTRITION 29 



amount of growth of many of the algae. This is clearly indicated 

 by the data to be presented on the nutrient requirements of 

 Coccochloris Peniocystis (Kiitz.) Drouet and Daily. 



Uni-Algal Cultures 



The lakes surrounding the city of Madison, Wisconsin, con- 

 tain profuse growths of numerous species of blue-green algae, as 

 well as green algae and diatoms, during the summer months, and 

 various methods of isolating certain blue-greens from these waters 

 have been attempted. The usual bacteriological techniques of 

 streaking lake water on 2% agar plates of Chu No. 10 nutrient 

 solution or pouring plates with small amounts of the lake water 

 added to tubes of melted agar were unsuccessful, however, be- 

 cause green algae and diatoms grew rapidly and covered the agar 

 surface before the desired blue-greens could develop. 



A micromanipulator was also tried as a means of separating 

 and removing algal cells or filaments from samples of lake water. 

 Under microscopic observation, single cells and filaments could 

 be drawn easily into a micropipette, but all except one species 

 failed to grow when transferred to Chu No. 10 agar slants or 

 solution. 



In the isolation procedure that proved to be most successful, 

 a heavy suspension of algae in lake water was collected with a 

 plankton net at a time when the species to be isolated was pre- 

 dominant. Small portions of this suspension were then inoculated 

 into a large number of flasks or tubes of Chu No. 10 solution. 

 The growth that occurred always consisted of a mixture of spe- 

 cies, but the cultures in which the desired organism was most 

 abundant were selected and subcultures prepared from them. By 

 repeated subculturing, uni-algal cultures were obtained. The fact 

 that the desired species often rose to the surface of the nutrient 

 solution or adhered to the sides of die flasks facilitated their sep- 

 aration. If the algae developed macroscopic colonies or filaments, 

 these were picked from the lake sample or nutrient solution and 

 washed repeatedly before subculturing to reduce the number of 

 contaminants. 



