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In the Illinois River 216 



In Spoon River 217 



In Quiver Lake 219 



In Thompson's Lake 219 



Complexity of the problem 220 



Lack of a common unit of measurement 220 



Chemical and plankton changes not proportional 221 



Causes of absence of proportional correlation 222 



Plankton only a part of the total organic nitrogen 222 



Utilization of organic nitrogen by plankton 224 



Observations on limnetic organisms 225 



Cumulative character of growing plankton 226 



Some correlations between movements in nitrogenous substances 



and plankton pulses 226 



With seasonal changes in free ammonia 227 



Comparison of plankton production with seasonal changes in oxygen 



consumed 228 



Comparison of plankton production with seasonal changes in chlorine 



in several localities 228 



Relation to sewage of Chicago, etc 230 



Chemical analyses 230 



Bacteriological examination 231 



At Havana 231 



Bridgeport to Grafton 232 



Seasonal changes in decay of sewage at Havana 233 



Complete mineral analysis 234 



Comparisons with other streams 235 



Vegetation 236 



Characteristics of aquatic vegetation at Havana 236 



Annotated list of aquatic plants at Havana 237 



Vegetation at plankton stations 241 



In Illinois River 241 



In Spoon River 243 



In Quiver Lake 244 



In Dogfish Lake 244 



In Phelps Lake 245 



In Thompson's Lake 245 



In Flag Lake ,. 249 



Plant zones 250 



Relation of depth to zones 250 



Inapplicability of Magnin's classification 250 



Pieter's classification 251 



Quantitative Investigation of the Plankton 253-574 



Purpose 253 



Method of Collection 253 



Changes during progress of the work 253 



Smith oblique-haul method 253 



Pump method 254 



