224 
organic nitrogen—certainly less than 50 per cent. and on the 
average much less than 33 per cent., which figures represent 
the total organic nitrogen, both plankton and silt, in suspen- 
sion. The fluctuations of the organic nitrogen contained in 
the plankton are thus masked by the predominance of the dis- 
solved form, and by the undetermined quantity of nitrogen- 
containing silt. 
A second cause for the lack of proportional correlation 
between the movement in these nitrogenous substances and 
the plankton may lie in the utilization by the plankton itself 
of some forms of nitrogen included within the range of sub- 
stances reported in the analyses as albuminoid ammonia and 
total organic nitrogen. For example, some organisms of the 
phytoplankton may utilize as food such forms of organic nitro- 
gen in solution in the water as the amido-compounds and the 
humus acids. It may be that some of the animal wastes are 
turned into the more highly organized nitrogen of the phyto- 
plankton without passing through complete oxidation and a 
return to the inorganic nitric acid and nitrates. If this be the 
case the flux of nitrogenous matters may lie quite within the 
range of substances here discussed, and the movements in 
nitrogen incident to these changes will consequently produce 
no pulses in the common curves of these substances. When, 
however, the inorganic nitrogen enters largely into the ebb 
and flow of the nitrogen of the plankton, the possibility of a 
correlated movement of plankton and organic nitrogen be- 
comes apparent, though proportionate pulses in the two remain 
improbable so long as the organic but non-living nitrogen con- 
tributes also to the flux of matter involved in the plankton 
changes. 
That the phytoplankton, as other low forms of vegetation, 
may thus utilize organic nitrogen in some of its forms as food, 
has been rendered probable by the experimental work of Loew 
(96), Bokorny (’97), Maxwell (96), and Zumstein (799). The 
work of the latter is especially in point in this connection, since 
his experiments deal directly with a genus, Huglena, which 
