CULTURE METHODS 



THE CULTURE OF ALG^ 



200. Culture in aquaria. The most convenient forms of aquaria are 

 shallow glass dishes eight to ten inches wide, battery jars six to eight inches 

 wide, or other large glass receptacles. These should be loosely covered with 

 pieces of heavy glass to keep out the dust, and should not be filled more than 

 two thirds full of water. It is not generally necessary to aerate the water, 

 and cultures should rather be left to themselves to grow the forms with 

 which they are stocked, or to develop whatever types may appear. It is always 

 interesting, and frequently surprising, to see what growths will develop of 

 their own accord in aquaria. There should be no metal in contact with the 

 water of aquaria, and copper is especially poisonous. 



Some algae, such as the water net, JSydrodictyon, species of (Edogonium, 

 Coleochaete, Chora, Oscillatoria, and numerous one-celled forms grow readily 

 in aquaria. Other types are more difficult to cultivate, as Spirogyra and 

 other pond scums, and it is almost impossible to keep the red or the brown 

 marine algae alive for any length of time. Terrestrial species of Vaucheria 

 frequently grow luxuriantly over the earth of the flowerpots in greenhouses. 

 Algae are more likely to survive in aquaria when kept in the water of the 

 ponds and ditches from which they came. Such water may be filtered, and 

 the aquaria should be stocked with only a small amount of the algae. It is 

 not desirable to have animals such as snails or Crustacea in the aquaila, for 

 there is almost sure to be present a sufficient quantity of microscopic forms 

 to preserve a balance of animal and plant life. The aquaria are best placed 

 outside the room on window ledges, except in freezing weather, and they 

 should have very little, if any, direct sunlight. 



A. Knop''s solution. There are a number of culture solutions. One of the 

 best known is that of Knop, made as follows : 



potassium nitrate 1 gram 



potassium phosphate 1 gram 



magnesium sulphate 1 gram 



These three salts are dissolved in one half liter of rain water or fresh 

 tap water, that is tap water which has not been standing in metal pipes. 

 To this is added a solution of 4 grams calcium nitrate in one half liter 

 of similar water. There will be formed an insoluble precipitate of 



211 



