274 American Fisheries Society 



occurring through the Hberation of infinite numbers of tiny 

 bubbles of oxygen from the leaves of submerged plants, a by- 

 product of their metabolic process, photosynthesis. The re- 

 sults of the pond studies previously outlined being so indicative 

 of the value of certain plants of differing habit of growth in 

 pond culture — more ultimately of the value of dissolved oxygen 

 in different quantities — a number of observations on oxygen 

 content of three of the four type ponds were carried out in 

 1919. The banks of the original ponds having been destroyed 

 by high water and by the burrowing of crayfish, four new 

 ponds of larger capacity were built in another section of the 

 bayou supplied with the same vegetative environmental fea- 

 tures as had obtained in the former observations, with the 

 exception of pond 3, which was supplied with a heavy sub- 

 merged growth of Ceratophyllum in addition to a solid surface 

 mat of Lemna, Spirodela and Woffia. The new ponds were 

 supplied as follows : 



Pond 1. Submerged Ceratophylltim. 



Pond 2. Open surface; all visible vegetation removed. 



Pond 3. Heavy growth of submerged Ceratophyllum and heavy surface- 

 mat of Lemna, Spirodela, and Wolffia. 



Pond 4. No submerged vegetation, but a heavy mat of Lemna, Spirodela, 

 and Wolffia. 



Beginning our determinations approximately at the time 

 of the stocking in the year previous, and extending them 

 through August 15th, two weeks before the date of the seining 

 operations of 1918, twenty-six determinations of dissolved 

 oxygen for each pond were made, water samples being taken 

 at about 3.00 p.m. on days representing differing weather con- 

 ditions. The method of collection and determination of these 

 samples was that outlined in detail in Standard Methods of 

 Water Analysis. The determinations are listed and averaged 

 as shown in table on the following page. 



It will be noticed from this tabulation that the pond 

 with the open surface and the submerged vegetation, Cer- 



