18 JEAN DAWSON 



daily noticed in the waters near the free or east end of the ram- 

 part. It is in the least disturbed waters, however, that the 

 water plants are growing plentifully, and in some places are 

 fast capturing the waters. Char a is found growing luxuriantly 

 in these quiet waters while not a trace of it can be seen along 

 the improtected shores. It is found, however, growing in con- 

 siderable abundance in the deeper, quieter waters of the lake. 



In this habitat the following conditions prevail : Protection by 

 the rampart from severe wave action; exchange of water with 

 the lake; nearly full sunlight; little or no vegetable debris; 

 clear gravelly substratum; on the average, a medium amount of 

 water plants ; shallow water with a gently sloping shore ; and no 

 enemies so far as observed. 



c. Open Sedge Formation as a Habitat. Another habitat 

 occurs on the more protected shores of Kavanaugh Lake. The 

 filling in of this lake and vSnow's pond by the natural invasion of 

 sedges, goes on apparently in two somewhat different ways, 

 which are of importance on account of their influence upon the 

 snail's environment. The sedges on the west shore of Kavanaugh 

 Lake are rapidly pushing from the shore into shallow water and, 

 since they grow in isolated clumps there is as yet no severe struggle 

 for the possession of territory. As long as sedges grow in the 

 shallow water this method of sedge invasion is seen, but when 

 the deeper waters are reached, their outward march is checked 

 and then the open space between the clumps begins to fill in 

 with the sedges until fairly solid ground results. Meanwhile the 

 march into the deeper waters of the lake goes on very slowly. 

 Every inch of ground is contested by the mass of sedges growing 

 at the water's edge, as may be seen in the waters of Snow's 

 pond and Doyle's Lake lying one mile east of it. Approaching 

 Kavanaugh Lake from the west moraine, one first reaches the 

 so-called bottom land which not many years ago formed a part 

 of the open lake, but is now solid ground. Upon approaching 

 nearer to the lake upon this newly reclaimed land, it is seen 

 that the water becomes deeper and deeper and the sedges farther 

 and farther apart. One can walk out over the water for a rod 

 or more by stepping from one bunch of sedge to another. The 

 shallow water near shore furnishes a fairly good habitat for 

 Physa gyrina and perhaps would be very much more thickly 

 peopled with snails were it not for the fact that this is the region 



