NET PLANKTON OF LAKE MEN DOT A 



37 



tein. The space between the base line, that is, the zero line, and the 

 curve B in each case indicates that portion of the organic matter which 

 the crude protein comprises, while the area between the two curves 

 shows the remainder of the organic matter, such as the chitin, the carbo- 

 hydrates, and the fats. 



In general these curves show that a marked increase or decrease in 

 the organic matter is accompanied by a similar change in the crude 

 protein. Thus during corresponding periods, the curves representing 



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Fig. 12. — The amount of dry organic matter, of crude protein, and of ether 

 extract in the net plankton of Lake Mendota in 1912. Curve A represents 

 the organic matter, curve B the crude protein and curve C the ether ex- 

 tract. The curves show the number of milligrams per cubic meter of water. 



the latter possess the same general form as those for the organic mat- 

 ter. In some instances, however, there are minor differences between 

 the two sets of curves. In 1912, for example (fig. 12), there was a 

 perceptible increase in the organic matter between the last week in 

 June and the last week in July, but the crude protein remained almost 

 constant in amount during this time; in fact, it showed a slight de- 



