20 



Indiana University Studies 



Not only is this littoral region limited but it has very few aquatic 

 phanerogams growing on it. This latter condition may be the 

 cause of the former. The decay of large masses of these aquatic 

 phanerogams may be the source of nitrogenous or other soluble 

 compounds necessary to the development of a rich plankton 

 fauna and flora. It is of course possible that some common factor 

 may influence both the littoral and pelagic regions. 



The study of the food of Daphnia by Mr. Fisher and myself 

 makes it clear that these lakes possess large amounts of nanno- 

 plankton too small to be captured in a No. 20 silk net. The rela- 

 tion of their metabolism and decay to that of the grosser forms 

 is unknown. 



The pioneer and important work of Birge and Juday on the 

 oxygenless region of certain types of lakes and their fauna has 

 opened up a new and interesting field in lake economy. The 

 problems connected with this are essentially physiological. The 

 work on the oxygenless region of the lakes of Indiana, especially 

 Center lake, confirms the fact announced by Birge and Juday 

 that a rather large fauna exists under anaerobic conditions in 

 the hypolimnion of many lakes. A more careful analysis of the 

 conditions in this region and extended experimental work cer- 

 tainly will yield valuable results. 



In this paper no data are given for Eagle (Winona) lake. A 

 more detailed study of this lake is in progress and will be published 

 separately. 



