GASES IN WATERS OF WISCONSIN LAKES. 



1289 



into the cooler stratum, although the bottom water is practically or wholly devoid 

 of the gas. Their presence in small nmnbers shows that such a lake is not suited 

 to the species, and that, while it can adjust itself and survive under these unfa- 

 vorable conditions, it is unable to thrive. It is not known whether it spawns 

 under these conditions. There can be little question that the continuance of the 

 species in this lake is due to the fact that the cool water still retains a certain 

 amount of oxygen throughout the season. 



C Cb T 



2 4 6 8_ 10 12 14 16 18 20 22 



I 



2 

 3 

 4 

 5 

 6 

 7 

 6 

 9 

 10 

 II 

 12 

 13 

 14 

 15 

 16 

 17 



la 



19 



20 

 21 



^^0 T CGb 



Fig. 15. — Thousand Island Lake. August 13, 1907. 



C Cb T 



2 4 6 8 10 12 14 16 18 20 



Cb TC 



Fig, 16. — Stone Lake, August 22 



CONCLUSIONS. 



I have selected for illustration these series from among the hundreds of 

 similar observations that have been made by the Wisconsin Geological and Nat- 

 ural History Survey. I have not attemped to give any complete picture of the 

 story of the gaseous changes in any lake, and many of the most important rela- 

 tions and results have been left unmentioned. I have brought these cases to 

 your attention in order to illustrate two conclusions which are of importance. 

 The first is that the cycle of the gaseous changes in a lake illustrates more 

 readily and more conspicuously than perhaps any other facts could do what 

 maybe called the "annual life cycle" of the individual lake, showing both the 



B. B. F. 190S— Pt 2—39 



