TYPICAL SWAMP AREAS. 51 
part an island of considerable dimensions has been formed, 
composed principally of the remains of former vegetation 
and now supporting quite a variety of plants. As one 
comes south along the eastern shore, open stretches of 
water are found where the usual marginal growth of rushes 
has been interrupted. This may be related to depth of 
water, nature of substratum, exposure or manner of prop- 
agation. The latter thought suggests the question whether 
propagation here takes place by rhizomes extending in the 
soil under the water, or whether the seeds float a while, 
then sink and germinate. Associated with these open 
areas, there is found an erosion of the shore until a bluff 
is formed two or three feet high. This is the natural 
result of the action of the waves raised by the prevailing 
west winds upon a shore where there is no protecting 
fringe of vegetation. Extensive masses of the tubers and 
rhizomes of Scirpus fluviatilis help to bind together the 
soil of these exposed bluffs, the slow decay of the wiry 
rhizomes retarding the erosion to a considerable degree. 
An interesting point for investigation would be the change 
of condition which is now causing the erosion of an area 
which at one time was permitted to be deposited. Many 
of these old root remains are two feet beneath the surface 
and must have been in position a long time. The area 
immediately east of these little bluffs is level and raised 
only a few feet above the lake. It is occupied by gardens 
or small farms and the alluvial soil is cultivated to within a 
few feet of the water, a fringe of tall weeds occupying the 
edge of the bluff. The same weeds occupy a position 
corresponding to a similar depth of soil where there is no 
bluff, but where the protecting vegetation has permitted a 
marshy soil formation to the lakeward side of the weeds. 
The dominant forms are Ambrosia trifida, Amarantus 
retroflexus, Chenopodium album and Melilotus alba. In 
the open water of the lake there is a great abundance of 
strictly aquatic vegetation. Among the most important 
