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American Fisheries Society 



the bottom of each pond of layers of decaying vegetation, the 

 result of the annual deaths of aquatic plants. It is evident 

 that plankton abundance in ponds 3 and 4, which were thickly 

 covered with Lemna and Jussiaea, would be considerably de- 



s 



Oxygen 



. 



Gombusia 



creased, as the matted condition of the surface vegetation tends 

 to keep the temperature of the water under it lower. The 

 production of plankton may also be regulated to some extent 

 by the amount of light. The introduction of certain plants 



