338 PROCEEDINGS OF THE INDIANA ACADEMY OF SCIENCE. 



pounds which showed the greater part of the decrease. It was also true 

 that the content of the surface of the pehigic region continued to rise in the 

 spring after the stratification had liegun (See Figs. 2 and 3). So it would 

 seem that winter mixing is not the only, and perhaps not the main factor in 

 causing the increased nitrogen concentration. A considerable part of the 

 albuminoid increase in Avinter and spring is doubtless due to the sediment 

 of the bottom being stirred up, the lake being much rougher in spring than 

 in summer. 



Interesting questions outside the scope of this paper are suggested by the 

 relation of the various compounds to the thermocline (Fig 4). It may be said 



Fifi. — 4 (Set' Tabic 'l) \'iTlifal Scries taken rl Station C 



The dotted line marked T- 

 One .s))ace rejiresents, 5° F. 



T is the thermocline. 



here, however, that shortage of oxygen near the bottom probably accounts 

 for the behaivor of the nitrate and nitrite. Determinations of dissolved 

 oxygen made at various times by Dr. Will Scott show an average of about 

 1.5 CO per liter for the water of the bottom of the lake during the summer. 



B. LiTTOKAL Regions Where Plant (Irowth was Open Enough to Allow 

 Free Circulation of Currents Set up by the Wind. 



As might be expected these regions showed close similarity to the pelagic 

 region. The water mixed freely with that of the open lake, and local varia- 

 tions were slight. 



