﻿Nichols: The vegetation of Connecticut 199 



water like a raft. Along the western shore of one of the Twin 

 Lakes is a beautiful example of a floating mat which thus owes its 

 origin to Carex filiformis (Fig. ii) ; and similar mats are frequently 

 encountered in other sections of the state. Toward its lakeward 

 margin such a mat is usually thin, but farther away from the edge 

 it reaches a thickness of two feet or more and becomes firm enough 

 to support considerable weight. For some distance from its outer 

 margin, in cases where it is typically developed, the mat is actually 

 floating and is underlain by clear water. But in proceeding from 

 the margin shoreward the water underneath is "found to become 

 more and more full of finely divided matter until, at a variable 

 distance from the water's edge, the deposit is nearly solid and the 

 mat no longer floats".* The filling up of the open water under- 

 neath, and the ultimate grounding of the mat is brought about 

 very largely in the manner already suggested, namely, by the 

 dropping down of debris from the lower surface of the raft. Often, 

 owing to local conditions, the mat grows outward from the shore 

 so slowly that the water beneath the floating substratum becomes 

 filled out to its very margin. By the time the mat has grounded, 

 if not before, shrubs have asserted themselves as the controlling 

 element of .surface vegetation; and these in turn, as in the lake- 

 swamp succession already described, ultimately give way to trees. 

 Mat Formation due to Decodon. — But, on the whole, in Connecti- 

 cut the sedges are overshadowed as pioneer mat formers by certain 

 shrubs, notably Decodon verticillatus , The manner in which 

 this latter shrub not only brings about the formation of a floating 

 mat but accelerates the upbuilding of the surface as well, has been 

 admirably described by Davis. f Growing at the water's edge it 

 sends up slender, arching stems, many of which reach out over the 

 open lake, curving gracefully downward toward their tips until 

 they enter the water (Fig. 12). Here the stem becomes greatly 

 swollen, due to the formation of aerenchyma, and develops numer- 

 ous adventitious roots. The aerial part of the plant is herbaceous 

 and dies at the end of the growing season. But the swollen, 

 submerged portion of the stem becomes woody and perennial, 

 lives through the winter, moored in place, as it were, by the other- 



