Xll 



PAGE 



Variations in plankton, enumerative method 287 



Plankton in cross-section of river below Spoon River 287 



Effect of Spoon River and Quiver Lake 289 



General summary of data of distribution of plankton 289 



Validity of application of plankton method to streams 290 



Plankton production in Illinois River channel 291 



In 1894 291 



Collections, statistics, and hydrographic conditions 291 



Seasonal distribution 293 



Comparisons and summary 294 



In 1895 , 295 



Collections, statistics, and hydrographic conditions 295 



Extermination of plankton under the ice in February 296 



Apparent absence of vernal pulse 298 



Stagnation pulst in June 299 



Phenomenon of recurrent pulses in production 300 



Discussion of the August-December pulses 301 



Comparisons and summary 306 



In 1896 307 



Collections, statistics, and hydrographic conditions 307 



The winter plankton 307 



The vernal pulse 308 



Discussion of May-August pulses 310 



Autumnal plankton '. 314 



Comparisons and summary 314 



In 1897 315 



Collections, statistics, and hydrographic conditions 315 



Plankton of first half-year 316 



Discussion of July-December pulses 317 



Comparisons and summary 323 



In 1898 324 



Collections, statistics, and hydrographic conditions 324 



Discussion of the January-March pulses 324 



The vernal pulse in April-May 327 



Description and environmental conditions 327 



Factors causing the unusual vernal pulse 328 



Effect of flood on vernal pulse 330 



Discussion of June-December pulses 331 



Comparisons and summary 337 



In 1 899 337 



Statistics and hydrographic conditions 337 



Discussion of January-March pulses 337 



Conclusions and comparisons 340 



Comparisons with tributaries and backwaters 340 



Spoon River, Station M 340 



Environmental conditions 340 



Collections 341 



