8 University of Michigan 



LAKES (table i) 

 Brown Lake 



In most places, both in the Upper and Lower Lakes, two 

 definite shore zones could be separated. The outermost zone 

 was that of Potamogeton and was the more constant of the 

 two, as it occurred throughout the lakes at a depth of water 

 between 6 and 7>4 feet. Inside of this zone was that of water- 

 milfoil and horn wort, which extended in to a depth of about 

 17 inches. Throughout both of these zones the bottom was 

 very soft and mucky. 



Besides these two, a third, inner zone could be differentiated 

 in several places. It was very variable in width and biota, 

 but was clearly marked off in most places where it occurred 

 by the lack of the higher plants determining the other two 

 zones. 



The main irregularities of these zones could be divided into 

 two classes: the invasions of the river conditions, and the 

 patches of water lilies which occurred throughout the middle 

 zone, but were particularly numerous near these river inva- 

 sions. Both of these affected the inner zones more markedly 

 than the outer. 



Habitat i. Water-weed Zones. Between the depths of 17 

 inches and 75^ feet, a luxuriant growth of aquatic vegetation 

 completely covered the bottom and reached to the surface of 

 the lake. Throughout this region and beyond it a deep layer 

 of soft, finely-divided, peaty muck covered the bottom of the 

 lake. 



The vegetation of this region could be subdivided into two 

 quite distinct zones, as has already been mentioned. In the 

 outer ones, Potamogeton richardsoni, P. pectinatiis and P. pcr- 

 foliatiis dominated near the surface and Utricularia znilgaris 



