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Affected by environmental factors. 510 



Approximation in time of pulses at different stations 510 



Normal regimen in our waters one of recurrent pulses of varying am- 

 plitudes 511 



Source and maintenance of potamoplankton 511 



Problem stated 511 



Relation of seepage waters 512 



Relation of tributary streams 513 



Examination of Quiver Creek 514 



Collections and method 515 



Constituents of Quiver Creek plankton 516 



Comparison with plankton of river 517 



Quiver Creek a diluent of channel plankton 518 



Relative numbers of species in tributaries and river 519 



Chemical conditions 520 



Examination of Spoon River 521 



Comparison of chemical conditions in Spoon and Illinois rivers. . . 521 



Resources of Spoon River adequate for large plankton 522 



Lack of time for breeding a cause of barrenness 523 



Comparison of quantitative plankton production in Spoon and 



Illinois rivers 523 



Errors resulting from leakage and silt 523 



Statistics of production by monthly averages of all collections. . 525 



Ratio of production 526 



Comparison of statistics of coincident catches 527 



Cause of periods of relatively larger production in Spoon River. 528 



Quantitative effect of access of tributary water formulated 529 



Qualitative analysis of plankton of Spoon and Illinois rivers 530 



Contrast in total population 531 



Relative development of different groups 531 



Algae 531 



Diatoms 532 



Rhizopoda 533 



Mastigophora 533 



Water-bloom of Spoon River 533 



Infusoria 534 



Rotatoria 534 



Entomostraca 536 



Insect larvae 536 



Comparison of total number of species 537 



Comparison of seasonal routine 537 



Contrasts in autumnal plankton 538 



Applicability of conclusions to other streams 539 



Effect of tributaries upon channel plankton 539 



Relation of backwaters to channel plankton 540 



Complexity of the problem 540 



Impounding action of flood-plain 541 



Amount of impounded water 541 



Duration of impounding 54 2 



