492 



Plankton of Thompson's L,ake, 1894-99 and 1909-10 

 Cubic Centimeters to the Cubic Meter 



Averages for March, April, and May: 

 1895-96 to 1897-98 10.89 

 1909-10 11.68 



Comparing the two years for these three months only, we find 

 the plankton average for 1897-98 to be 6.31 cubic centimeters, and 

 that for 1909-10 to be 8.97 cubic centimeters. If, however, we com- 

 pare the average for these two years entire, the yield for the former 

 year is 9.39 and that for the latter is y.'/'J. If, on the other hand, 

 we take for comparison the plankton yields for ]March, April, and 

 May of all three years, from September, 1895, to August, 1898, in- 

 clusive, we find these to average 10.89 cubic centimeters as compared 

 with 11.68 for the year 1909-10. It would appear, consequently, 

 that there is no notable change to be made out in the productivity 

 of the waters of the lake per unit of volume, as compared with the peri- 

 od preceding the opening of the drainage canal. It is to be noted, 

 however, that the very much greater average area of this lake under 

 present conditions, and the much larger, freer, and more continuous 

 contributions to the river made by it at the higher levels must, of 

 course, be taken into account in any discussion of the causes of the 

 much richer plankton of the river itself. 



Ouher Lake. — Quiver Lake, at stages low enough to separate it 

 from the main stream, is a mere broad bay of the Illinois, opening 

 widely at its lower end, receiving the waters of Quiver Creek above, 

 and fed in part by many springs along its high, steep, and sandy 

 eastern bank. It was formerly clogged with vegetation in midsum- 



