106 BOTANICAL GAZETTE | FEBRUARY 
trees to flood plains is not strange, since in such habitats are given 
the most congenial conditions that can be found in our area. 
The vegetation on flood plains is not always as described 
above. Sometimes meadows are found instead of forests; this 
condition is particularly well shown along Thorn creek. Fig. 18 
shows a stretch of meadow of this type. Besides various grasses 


Fic. 18.—Flood plain of Thorn creek near Glenwood, showing a meadow instead _ 
of aforest. At the center is an uneroded island, detached from the morainic main- 
land, seen at the left. The vegetation of the island is similar to that of the morainic 
plands. 
(such as Poa pratensis and Agrostis alba vulgaris), there are often 
other plants in abundance, ¢. g. Thalictrum purpurascens, Fragaria 
Virginiana, Anemone Pennsylvanica. The ecological meaning of the 
meadow is not clear. Probably mowing or grazing is responsible 
for the failure of a mesophytic forest to develop. Extensive 
thorn (Crataegus) thickets sometimes occur in these meadows 
and probably betoken the beginning of a mesophytic forest. 
Extensive and apparently natural meadows are found in the 
Calumet valley. 
As we have seen, the climax type of vegetation on the flood 

