1901] PHYSIOGRAPHIC ECOLOGY OF CHICAGO 153 
bog margin flora without a bog; a shallow trench has been dug and 
in this trench there have appeared various peat bog plants, e. ¢., 
Sphagnum. These considerations show that bog margin floras, 
though associated with most bogs, are not necessarily genetically 
connected with them. 
A word may be said about undrained swamps among the 
active dunes. The conditions here, of course, are far more 
severe than in ordinary peat bogs and only a few species are 


Fic. 23.— Pond at Waukegan almost destroyed by bulrushes. 
able to endure in such a habitat. The most typical herb is /uncus 
Baltcus littoralis. Seedlings of the cottonwood, as well as the 
long-leaved and glaucous willows, germinate in these wet depres- 
sions. Reference will be made to these plants in connection 
with the dunes. 
In the morainic portions of our territory there are few if any 
peat bogs as described above, although they are usually more 
typical of moraines than of other topographic areas. On account 
of the clay soil which characterizes the morainic uplands there 
are many patches of swampy woods throughout the district. 
Shallow depressions of this type in sandy soil would not have a 
swamp developed. Morainic forest swamps are characterized by 
several trees, viz.: the bur oak, swamp white oak, and scarlet 
