456 



General Botany 





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Fig. 277. Food relations of aquatic life. No matter how long the chain of animals is 

 up to the fish, the fundamental food organisms are the algae that transform inorganic 

 materials into foods. 



algae thrive best in shallow water, and it is from the algae that the 

 small animals on which the fish feed secure their food. 



But while the algae are a source of food for water animals, they 

 are also a source of annoyance in reservoirs in which drinking 

 water is stored. When they accumulate in large quantities and 

 die, they cause the so-called '' fishy taste " of water. This 

 trouble has been to some extent controlled during recent years 

 by the exclusion of light from small reservoirs, and by the addi- 

 tion of small amounts of copper sulfate to the water in large 

 reservoirs. Copper sulfate is very poisonous to algae, even in 

 quantities of one part to a million parts of water. Since animals 

 are not injured by such small amounts, the water may be used 

 without harm for drinking purposes. 



Periodicity of algae. The fresh-water algae show somewhat the 

 same periodicity of development, reproduction, and dormancy 

 that is shown by the more familiar land plants. There are six 

 general seasonal classes that may be distinguished. There are 

 winter annuals, whose spores germinate in the autumn and 

 which increase during winter thaws by cell division and swimming 



