378 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 2 



soon appeared on the gelatin, so that successful transfers of two 

 species of algae, Scenedesmus acutus Meyen and Ghlorella vulgaris 

 Bey. were made to other media. 



One of the earliest methods employed for isolating algae was to 

 pour a drop of water containing the algal cell desired for study in a 

 20 per cent gelatin solution or a 1.5 per cent agar solution which had 

 been slightly cooled but not sufficiently cooled for solidification in a 

 petri dish. By growing the culture in north light and observing jt 

 day by day under the microscope, algal cells were soon seen to sepa- 

 rate from the original colony. These cells could be removed with a 

 loop of fine platinum wire and placed in a new plate of sterile media. 



Kriiger (1894), Tischutkin (1897), and Ward (1899) were among 

 other early workers to obtain pure cultures of algae by plating in 

 agar or gelatin. Chodat and his pupils (1902) isolated species by 

 placing pieces of sterilized unglazed porcelain in contact with a 

 mineral nutrient solution. Repeated transfers were made to fresh 

 sterile plates until a pure culture was obtained. In cases where there 

 were a few algal cells among numerous bacterial and fungous cells, 

 they used a mineral nutrient solution that was favorable to the 

 growth of the algae and unfavorable to other organisms. 



Pringsheim (1926) advocates silica-gel plates for isolating differ- 

 ent species. Van den Honert's (1930) modification of his formula 

 is highly satisfactory. Water glass is diluted to a specific gravity 

 of 1.08 by means of a hydrometer. Ten cubic centimeters of this 

 fluid is added to 7 cubic centimeters of normal hydrochloric acid 

 and quickly mixed. The mixture is poured into petri dishes, where 

 it gelatinizes immediately. The plates should be washed in running 

 tap water for one day to wash out any remaining hydrochloric acid, 

 then washed with distilled water and covered with nutrient solution. 

 After 24 hours, the nutrient salts having penetrated into the silica- 

 gel, the remaining solution should be poured off. Place a drop of the 

 water containing the alga in sterile solution and pour it over the 

 silica-gel plate. After a few moments pour off the water. Within 

 two weeks' time the green algal cells will appear growing on the 

 silica-gel and they may then be transferred to other sterile plates, 

 repeating until a pure culture is obtained. On these silica-gel plates 

 there is an even smaller development of bacteria and fungi than on 

 agar plates. 



The method that produces the most satisfactory results is that of 

 placing about 10 cubic centimeters of the pond water containing the 

 cells in 100 cubic centimeters of the solution described above. After 

 several clays, 10 cubic centimeters of this solution may be placed in 

 sterile solution. When this has been repeated several times, a drop 

 of the latest inoculated solution may be grown on the agar medium. 



