A LIMNOLOGICAL RECONNAISSANCE 53 



times as great in the former lake as in the latter. On the 

 assumption that the amounts in this table represent a fair 

 average per cubic meter of water for the whole lake, a com- 

 putation based on these figures gives an average of 222.2 kg. 

 per hectare of surface for lake Mendota in 1915, or 198 

 pounds per acre. The quantity in 1916 was about 6"^ less 

 than this amount. This is nearly four times as much as 

 was found in West Okoboji lake in 1919. The quantity of 

 total plankton has been determined for only a few of the 

 Wisconsin lakes, but, of those on which determinations have 

 been made so far, only one falls as low as West Okoboji 

 lake. The total plankton of Devil's lake, Wisconsin, on 

 August 27, 1919, amounted to 500 mg. of dry organic mat- 

 ter per cubic meter of water, or about 2^'c less than that of 

 West Okoboji lake. This result for Devil's lake means a 

 much smaller amount per unit of area since it is a much 

 shallower lake ; that is, it represents only 44.5 kg. per hec- 

 tare, or approximately 40 pounds per acre. On the basis 

 of these results both of these lakes must be classed as 

 plankton poor. 



TABLE 26 — This table gives the number of milligrams of organic 

 matter per cubic meter of water in the net plankton and 

 in the nannoplankton of lake Mendota and of Okoboji lake 

 in the years indicated. The quantities given for the for- 

 mer lake ai-e the averages of the last week im July and 

 the first week in August each year, while those for the 

 latter lake were obtained in obsen^ations made on July 

 31, 1919. 



BOTTOM FAUNA 



Some samples of mud were obtained from the bottom in 

 the deeper water by means of an Ekman dredge. This 

 material was sifted through a fine meshed net for the pur- 

 pose of ascertaining the number and variety of the macro- 

 scopic fauna of the bottom. The time that could be devoted 

 to this work was very brief so that hauls were made at only 

 two different depths, namely, 21 m. and 33 m. The results 

 obtained from the samples are shown in table 27 ; they give 



