Barney and Anson. — The Top-Minnow 



275 



atophyllum, averaged 5.73 parts of dissolved oxygen per mil- 

 lion, the average amounts for each of the other ponds being 

 lower. The lowest average record was 0.26 parts per million 

 for the pond with the heavy mat of vegetation and with no 

 submerged plants. The pond with a similar mat of vegetation 

 but containing a quantity of submerged plant growth averaged 

 nearly five times this record, with 1.23 parts per million. The 



Dissolved Oxygen Content of Experimental Ponds 



pond with the entirely open surface and none but microscopic 

 vegetation yielded an average record of 4.80 parts of dissolved 

 oxygen per million. The cause of the variation in dissolved 

 oxygen content in each individual case seems to be evident. 



