222 
Three causes may be assigned in explanation of the absence 
of proportional correlation in the flux of these nitrogenous sub- 
stances and of the plankton, all of which are operative, but in 
varying effectiveness at different times and under different 
conditions. 
In the first place, the plankton itself constitutes but a part 
of the total organic nitrogen; how small a one the data at 
hand do not determine. Barring out error arising from the 
death of the plankton and from the solution of the products 
of its decay which might take place during the interval 
between the collection and analysis of the sample, we find in 
the relative amounts of albuminoid ammonia and total organic 
nitrogen in solution and in suspension respectively some eyi- 
denceas to the possible limits ofthe proportionate amount which 
the plankton and silt together form of the total nitrogenous 
substances. The average amount (Table X.) of albuminoid 
ammonia in solution and in suspension from July 6, 1897, to 
March 28,1899, is .855 and .181 parts per million respectively. 
Plankton and silt together thus constitute about one third of 
the total albuminoid ammonia in the Illinois River. The rela- 
tive amounts of dissolved and suspended albuminoid ammoniaat 
the weekly intervals of analysis fluctuate according to access of 
flood waters and increase in the plankton. The former is the 
more potent factor. Usually the amount in suspension is from 
one third to one half that insolution, rarely equaling or surpas- 
sing it, as in the flood of February, 1898, when it rose to .4 as 
compared with .28in solution. The plankton pulse of April-May, 
1898, accompanies a rise in total albuminoid ammonia from .4 
to .6—an increase of 50 per cent. The increase lies almost 
entirely in the suspended form, which rises from a previous 
level of .04 to .08, to .08 to .20, that is, it is more than doubled. 
The volumetric increase in the plankton is, however, over 
thirty-five-fold. Thus, under the most favorable conditions, 
receding flood, little silt, and plankton maximum, the increase 
in suspended albuminoid ammonia attending a thirty-five-fold 
increase inthe plankton constitutes but 33 per cent. of the total 
