512 



newal, — the channel from Utica to the mouth discharging in 

 from 5 to 25 days, according to the rate of the current,— the 

 plankton is continuously maintained, and the seasonal routine 

 is run in the face of this continuous renewal of the water. 

 Furthermore, the plankton product of the stream is discharged 

 at the mouth of the river practically in its entirety, for the or- 

 ganisms of the plankton cannot maintain their place in the 

 stream against the current. The only organisms of the pota- 

 moplankton which remain, are those used as food by fishes and 

 other animals which are not carried away by the current, and 

 such as may be lodged — usually in encysted, and thus heavier, 

 condition — along the bottom or banks of the stream. At times 

 of flood the receding waters leave some of the plankton side- 

 tracked in the reservoir backwaters — in the lakes, lagoons, 

 bayous, and marshes of the bottom-lands. As river levels fall 

 it may be slowly drawn off into the channel of the stream, or 

 cut off from connection with the river. This continual dis- 

 charge of the plankton, never to return, makes the problem of 

 the maintenance of the potamoplankton, quantitatively at 

 least, very different from that of the maintenance of the plank- 

 ton in a lake. 



Three suggestions arise in explanation of the perennial 

 character of the plankton of the river: (1) The plankton en- 

 ters with the tributary waters, in which case the problem is 

 only removed a step; (2) it is autonomous, developing in the 

 stream while the waters are in transit, in which case the solu- 

 tion lies in the river and its environment; or (3) the two elements, 

 contribution and autonomy, are combined, in which case the 

 share of each will appear on a comparison of the plankton of 

 the river and of its tributary streams and backwaters. 



The water in the channel of the river comes from three 

 sources ; from springs and seepage along the banks, from the 

 impounded backwaters of the bottom-lands, and from tributary 

 streams. 



EELATION OF SEEPAGE WATERS. 



The contribution from springs and from seepage are incon- 



