TOTAL PLANKTON OF LAKE MENDOTA 103 



smaller depth than this and too low for the areas with a greater depth 

 of water. This method of stating the results would show the actual 

 conditions only in a lake with straight sides and a uniform depth. 

 Taking the variations in depth into account would complicate the prob- 

 lem too much and the discussion is confined, therefore, to the averages 

 for the total area of the lake. 



In computing the results for the entire area of the lake, the monthly 

 averages per cubic meter of water were ascertained from table 24 and 

 these averages were then multiplied by the mean depth of the lake 

 (volume-^area=mean depth). The results of these computations are 

 shown in the second part of table 26 in which the amounts of organic 

 matter are indicated in kilograms per hectare and in pounds per acre. 

 The quantity per unit of area, when the total surface of the lake is 

 considered, is a little more than 55.0 per cent of that found in the deep 

 water as shown in the first part of this table; that is, by this method 

 of calculating the results, approximately 45.0 per cent of the material 

 noted in the deep water is attributed to the shallower water. On this 

 basis the amount of dry organic matter in the total plankton varies from 

 a minimum of 141.4 kilograms per hectare (126 pounds per acre) in 

 February to a maximum of 287.5 kilograms (256 pounds per acre) in 

 December, or slightly more than a twofold variation. The living ma- 

 terial, on the other hand, would weigh at least ten times as much as 

 this. 



