221 



and its interpretation, in many cases at least, becomes probable, 

 if not, indeed, certain. 



In the first place it may be noted that the fluctuations of 

 the plankton are not paralleled by proportionately great move- 

 ments in the total nitrogenous substances in the water which 

 enter largely into their composition. For example, the spring 

 maximum of the plankton is accompanied by no such wave in 

 these substances. Indeed, a slight ripple of depression seems to be 

 the only concomitant fluctuation. Even granting a large mar- 

 gin because of the al^sence of a common unit of measurement, 

 it remains apparent that the fluctuations of the substances in 

 question and of the plankton are not proportional . A single 

 illustration, found in the spring maximum in Quiver Lake in 

 1898 (PL XLIX.), will suflice to make this point clear. The 

 following table, drawn from Table XIII., gives the amounts of 

 plankton and of the several forms of nitrogen present before 



Quiver Lake. 



Per cent, of Change. 



April 19 to 

 May 3... 



-|-ioo 



-27 



—19 



33 K 



-46 



+39QI 



(April 19), during (May 3), and after (May 11) the plankton 

 wave, and the extent of the change, in per cent., of the amount 

 present on the 19th which each exhibits. The plankton rises 

 from 1.03 cm.' per m.' to 42.14, falling subsequently to 4.70 and 

 1.97. This is an increase of 3991 per cent. No one of the ni- 

 trogenous substances in the table exhibits a change exceeding 

 100 per cent., and the average change is only 45 per cent. In 

 this case the change in plankton is eighty-eight times as great 

 as that in the average of all forms of nitrogen, assuming, of 

 course, that the units of measurement are comparable, 



