1905] BROWN—THE PLANT SOCIETIES AT YPSILANTI 271 
of the flora of the so-called undrained swamps. This stage does not 
appear to have been uncommon in the wider parts of the valley, and 
possesses points of unusual interest. This association forms a cres- 
cent-shaped area at the base of the cemetery bluff, commencing with 
the seepage springs (fig. 2 and map) and reaching stream-ward as 
far as the water sedge. It is here 700 feet long and 200 feet wide, 
containing the following species listed in order of their relative 
abundance: Scirpus americanus, Carex filiformis, Koellia flexuosa, 
Lysimachia quadrifolia, Campanula aparinoides, Lobelia Kalmii, 
Aster junceus, Parnassia caroliniana, Rynchospora alba, Gerardia 
paupercula, Solidago Riddellii, Sarracenia purpurea, Larex laricina 
(once abundant, but now removed for firewood). 
On comparing the composition of this society with that of others, 
it was found that the above species are peculiar to the one society 
and occur rarely if at all outside of it. A sharp line of separation 
occurs between it and neighboring societies. As a whole it may be 
said that the vegetation is the most distinct of all those studied. 
With but two exceptions all species are perennials, and a certain 
likeness of form characterizes the members, as if mutually adapted 
to xerophytic conditions, causing the vegetation to stand out in 
contrast with the neighboring broad-leaved hydrophytes. Regarding 
this group of plant societies the following points are to be noted. 
1. Of the whole group, 5 per cent. of the species were found to 
be submerged, 32 per cent. amphibious, and 63 per cent. terrestrial. 
€ willow society is richest in species, containing more than twice 
- umber of species found in any other society of this group, and 
ghtly more than any society to be discussed later. 
2. Of the agencies active in filling the bayou, the first place is 
ee to vegetation (fig. 3). Not more than one-third the material 
_ came the composition of earth so formed is inorganic matter, 
Proportion often being smaller. From the areas of organic soil 
uently occurring along the flats it is plain that the process has 
as active in past as in present times, converting numerous stand- 
: em and deserted channels into dry land surface supporting 
y forest growth. ; 
eae of the common species are gregarious, and tension lines 
y marked. : 
ing 
