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 ('99). The 

 work of the latter is especially in point in this connection, since 

 his experiments deal directly with a genus, Euglena, which 



