368 



era side can a substratum of harder sandy clay be reached be- 

 neath two or more feet of this deposit. With the exception of 

 a narrow fringe along the eastern side, the vegetation lacks the 

 lilies, rushes, sedges, and other emergent plants which charac- 

 terize the eastern shore and northern end of Quiver Lake proper 

 (PI. XVII. ). It consists (PI. XVIII.) almost exclusively of Cer- 

 atophyllum, Elodea, and Potamogetons, which, in the low water 

 of 1895, represented in the plate, filled the lake from center to 

 periphery. Irregular openings in this dense growth appear oc- 

 casionally in the area, and are modified by the shifting of the 

 lightly attached vegetation, by wind, and by flood water. 



Except at high water and during the rapid run-off of im- 

 pounded backwaters no appreciable current traverses this area. 

 It receives no immediate contributions of spring or creek water 

 along its margins, but depends entirely upon backwater from 

 Quiver Lake or flood invasions for its supply. 



The examination of the plankton content of its waters ac- 

 cordingly affords an opportunity to test the effect of this im- 

 pounding factor, and also serves to throw some further light on 

 the effect of vegetation on plankton development in impounded 

 waters. 



COLLECTIONS. 



The collections in this lake cover a period of two years — 

 from April 29, 1895, to June 28, 1897 (Table VI.). They num- 

 ber 48, and are distributed in much the same manner as those 

 in Quiver Lake in the same period. The collections of 1895 and 

 those of 1896 through May 8 were all made by the oblique-haul 

 method with the single exception of that in the flood of Feb. 

 27, which was one of repeated vertical hauls. The collection 

 of May 19, 1896, was made in the midst of rapidly growing veg- 

 etation by dipping from surface waters, which then afforded no 

 area suitable for an oblique haul. The oblique hauls were made 

 for the most part near the center of the lake in a channel freed 

 from vegetation a day prior to the collection. From May 21, 

 1897, all collections were made by the plankton pump in open 

 stretches of water amid the vegetation. 



