1901] PHYSIOGRAPHIC ECOLOGY OF CHICAGO 105 
Canadensis), seen in the foreground, the papaw (Asimina triloba), 
the sycamore (Platanus occidentalis), and the hackberry (Celtis 
occidentalis). In other flood plains there may be found the 
mulberry (Morus rubra), the red bud (Cercis Canadensis), the 
buckeye (Aesculus glabra), and the tulip (Liriodendron Tulipifera). 
None of these trees are common in our district, and only Celtis 





Fic. 17.—A dead oxbow lake in the flood plain of Thorn creek. A willow still 
remains at the right, while the shrubs (Cephalanthus) have closed in upon the lake. 
may be regarded as frequent. These relatively southern trees 
are found not only along the Desplaines and its tributaries, 
where there is supplied a continuous habitat along the river 
southward, but also along the Calumet and its tributary, Thorn 
creek. The occurrence of the tulip tree is full of interest, since it 
has been found thus far chiefly (perhaps only) in the vicinity of 
the dunes. Its occurrence has been noted especially at Chester- 
ton along a small stream which empties into Lake Michigan at 
that point; the tulip tree has also been found away from present 
Streams, but apparently in old valleys whose streams have been 
diverted by dune activity. The confinement of these southern 
