XVlll 



PAGE 



Representative character of our data 543 



Predominantly higher production in backwaters 543 



Causes of periods of low production in backwaters 544 



Summary of statistics of channel and backwater production 544 



Indigenous plankton of channel 545 



General summary * 546 



Total annual production 547 



At Havana 547 



At mouth of river 548 



Variation from year to year 548 



Total annual loss of organic matter from Illinois River 549 



Determination of total production as affected by leakage through silk 



net 549 



Volumetric determination by means of filter-paper catches 549 



Character of silt in these catches 550 



Filter-paper catclies not suited for volumetric work 51,0 



Confirmation of my results by the work of Lohmann 550 



Methods of making filter-paper catchts 551 



Statistical data of silk and filter-paper catches 552 



Ratios 554 



Seasonal changes in ratios 555 



Volumetric methods imperfect as a test of productivity 556 



Comparison with other bodies of water 556 



Absence of comparable data 557 



Comparison with Danube (Steuer) 557 



Comparison with New England streams (Whipple) 557 



Comparison with Elbe (Schorler) 558 



Comparison with Oder (Zimmer and Schrceder) 558 



Omission of comparisons with lakes 51^8 



Does geographical position determine planktograph? 559 



Comparison of maximum production 559 



Statistical data 560 



Relative productivity of Illinois waters 560 



Location of seasonal maxima 561 



Economic Considerations 561 



Illinois River as a source of wealth 561 



Value for sport and recreation 561 



Are resources now utilized to advantage ? 562 



Relation of plankton to fisheries 563 



As food of fishes 563 



Importance of knowledge of plankton in scientific aquiculture 564 



Comparison of annual product of fisheries and plankton 5(35 



Statistical data 565 



Correspondence in data 566 



Annual wastage and fish production 567 



Suggestions for utilization of resources 567 



Conclusions 569-574 



Tables 575-6i8 



Bibliography 619-624 



Explanation of Plates 625-628 



