NUTRIENT MEDIA 321 



culture of algae, consists of 4 parts of calcium nitrate, i part of 

 magnesium sulphate, i part of potassium nitrate, i part of potas- 

 sium phosphate. These should be dissolved in sufficient 

 water to make a 0.2 per cent, solution of the combined 

 salts. The potassium salts should first be dissolved, then the 

 magnesium salt, and last the salt of calcium should be added 

 after having been dissolved by itself. By this procedure only a 

 small amount of insoluble calcium phosphate is formed. The 

 zoospores of Vaucheria may be induced to form at almost any 

 time by transferring this alga from the above solution, in which 

 it has been growing exposed to a bright light, to pure water; or 

 cultures in a o.i per cent, or 0.2 per cent, nutrient solution which 

 have been exposed to the light need only be placed in a dark 

 place in order to incite the production of zoospores. 



A 2 per cent, to 4 per cent, solution of cane-sugar may be used 

 as a nutrient medium for algae. Filaments of Spirogyra may be 

 made to conjugate by transferring them from the water in which 

 they have been growing to a solution of cane-sugar as above, 

 which is then placed in a well-lighted place. 



The formation of zoospores may be incited in (Edogonium by 

 transferring filaments of the alga from water at a low temperature 

 (say at the temperature of the early morning) to a 2 per cent, or 

 3 per cent, solution of cane-sugar which is kept at a constant tem- 

 perature of about 26 C. 



Convenient flasks for the preservation of sterilized fluid nutrient 

 media may be made from glass tubing as follows: A piece of 

 glass tubing 0.2 inch in diameter, or larger, is held with its lower 

 end in the flame of a blow-pipe, the tube being constantly revolved 

 about its long axis to insure an even heating of the end of the 

 tube until the end of the tube becomes soft and just begins to 

 draw downward in the form of a large drop. By this time the 

 mouth of the tube has become closed. Then quickly the tube 

 is removed from the flame, and while the melted end of the tube 

 is still held downward, air is blown in at the upper end of the 

 tube by means of the mouth, so that the molten glass at the lower 

 end of the tube is forced outward in the form of a rounded flask. 



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