270 BOTANICAL GAZETTE [octoBER 
by the waterlilies, sending out long stems with leaves clustered above. 
In this zone, when the surface of the water is quiet, occur such plants 
as Utricularia, Lemna, Spirodela, and Riccia. Peat-like material 
rapidly accumulates below as growth proceeds above. The inter- 
woven rootstocks are firm enough to support the weight of a person. 
The several kinds of water smartweed are most active in forming 
this mat, although the yellow pond lilies add a good deal of firmness. 
At length the intervening space between the surface growth above 
and the substratum below becomes filled in with an oozy accumula- 
tion of peat, and gradually two marsh societies appear, the Typha- 
Sparganium and the water sedge. These marsh plants are charac- 
terized by the possession of thickly matted root systems and rhizomes. 
Carex stricta is the deepest water sedge here. It appears on the 
advance of the line of sedges and forms tufts of great compactness 
and strength. These tufts persist through subsequent changes that 
occur, and long after the death of the sedge itself, finally become 
covered with Potentilla fruticosa and turf-forming grasses. They 
give rise to the peculiar mound or hummock configuration so charac- 
teristic of the numerous valley meadows which have been built up 
in this way. Sedges build up the peat bed in two ways: (1) by the 
death of the aerial parts; and (2) by the death of the roots and 
rootstocks, the latter often the more rapid of the two processes. 
As the surface becomes rather free from water and firm, there 
appear the first woody types. Shrubby species of Salix are the first 
to grow in abundance, covering many parts so densely that other 
forms are almost excluded. Rhus venenata, Naumburgia thyrsiflor 7 
Asclepias incarnata, and Scutellaria lateriflora act as pioneers 
seizing decaying timbers, islands of sedge, and similar places of 
advantage. This results in the formation of a willow or 
Swamp society, the vegetation of which is richer in individuals and 
species than that of any other association. From the map tt wil 
be seen that the arboreal species of Salix are confined chiefly to the 
ridge, which is mainly till in this portion. The shrubby kinds, i 
the other hand, prevail over the beds of black peat bordering the 
water. d 
_ Part of the drained swamp area has culminated in tamarack a 
other plants with xerophytic characters similar to those characterist 
