1905] BROWN—THE PLANT SOCIETIES AT YPSILANTI 283 
SUMMARY 
1. The bayou of Ypsilanti, as indicated in the sketch of its geo- 
logical history, is of relatively late origin, and relics of postglacial 
floras have been nearly obliterated by more recent changes, which 
render the portion of the valley directly affected by the stream not so 
suitable for the preservation of ancient floras as the secluded swamps 
~ 
Jun Ohad ~ 
Sumae av ve 
Black gs pss i, fa ss Lad cn oie vss ounvie soos s S010 Seb ee eld waediew ay hae cenwen y Wem euerae eter 
Ook. Aickory. Weg 
Walnut... ...-. P 
I Ed 
Moist ee ee NS esd. 
Toma rach... 
ee. 
ee tetee UN | 
Iypha-Sparganinen:. ot AS 
Water-Smortweed...™...... 
Water Os eee 
Pond weed 
Fic. 5.—A, curve of period of bloom; B, curve of geographical distribution; 
“arves drawn from values obtained in map. 
or bogs of the morainal regions. But the seepage springs and bluff 
€Xposures of sufficient age and isolation still retain such relicts of a 
Past northern flora which followed closely the retreat of the ice. 
2. The societies of river swamps, such as the bayou here described, 
ate distinct from those of the lake swamp or bog. In both, however, 
sTophytic adaptations are conspicuous, which cannot be explained 
acid es drainage currents nor by the presence of humus 
8. 
3: The peat-forming societies show sharp tension lines, conforming 
to depth 
of water, characteristic of pond vegetation. Such tension 
