Miscellaneous Classes 135 



ordinary inorganic or organic culture media made up in seawater. Miquel 

 seawater is very satisfactory. [See p. 33.] 



D. salina tends to die out in competition with other organisms, except 

 in inorganic media containing 10-20% NaCl. It should, therefore, be 

 kept in a stock culture of Miquel seawater plus 10% NaCl, or in some 

 other equally concentrated medium, and subcultured (if necessary) in 

 a more dilute medium before use. 



The cultures should be kept in strong light, though direct sunlight 

 should be avoided in young cultures. The organism can grow through- 

 out a wide temperature range, but 30 C. or just below seems to be 

 optimal. 



Dunaliella viridis is always green, and is much smaller than D. salina. 

 It seems to do best in a medium of 5-10% salinity. Otherwise, the 

 statements made about D. salina hold equally true for this organism. 



Platymonas subcordaeformis is a small, green 4-flagellated alga. It 

 is found in saline waters (up to 8-10% salinity) in warm-temperate re- 

 gions, and is probably of wider range than has been reported. It is 

 frequently found, often in very rich cultures, in spray-pools above tide 

 line on rocks frequented by sea birds. It may sometimes be recovered 

 from seawater. 



It grows rapidly and well in seawater (even considerably diluted sea- 

 water) to which Miquel's solutions have been added, so that no concen- 

 trated stock culture is required. 



Light and temperature requirements are as for Dunaliella salina. 



Reference 

 For the culture of Ankistrodesmus see p. 227. 



WHEAT-GRAIN INFUSION 



John W. Nuttycombe, University 0} Georgia 



THE culture medium here described has been used constantly 

 for nine years and has proven extremely satisfactory for culturing a 

 wide variety of aquatic invertebrates. Its chief advantages lie in the 

 ease of preparation, wide range of use and the relatively long period 

 of time required for the culture to reach its maximum. 



In practice we add 200 or 300 grains of seed wheat to about 250 cc. 

 of spring water in a flask. This is heated over a burner until the 

 water comes to a sharp boil and is then allowed to cool. If it is desired 

 that the cultures reach a maximum more quickly the boiling is con- 

 tinued for several minutes so as to make the contents of the wheat grains 

 more quickly available. 



We usually boil spring water to kill the free organisms in it, allow it to 



