
86 BOTANICAL GAZETTE [FEBRUARY 
is remarkably tortuous, involving constructive and destructive, 
progressive and retrogressive phases. The treatment begins 
with an erosion gully; then there follow in order the ravine, 
both in clay and in rock, the xerophytic bluff, and the mesophytic 
forest. The depositional phases of the river begin with the 
appearance of a permanent stream; then follow the various 
stages of the flood plain culminating in the mesophytic forest. 
The swamp series begins with the pond, treats next the various 
types of swamps and ends with a brief discussion of the prairie. 
In the upland series the various stages of the rock hills and 
then of the clay hills are taken up in turn, culminating in the 
mesophytic forest. The coastal group is next discussed, begin- 
ning with the lake bluff. Finally, there is a brief treatment of 
the dune series from the beach on through the embryonic and 
active dune to the established dune on which there finally appears 
the mesophytic forest. 
II. The plant societies. 
A. The inland group. 
I, THE RIVER SERIES. 
A. The ravine-—No topographic forms lend themselves so 
well toa physiographic sketch of the vegetation as do those 
that are connected with the life history of a river. Beginning 
with the ravines, which are deep and narrow, because of the 
dominance of vertical cutting, we pass to the broader valleys, 
where lateral cutting becomes more pronounced. From this 
stage on we have to deal with two phases of river action, the 
destructive, which is concerned with the life history of the bluff, 
and the constructive, which has to do with the development of 
the flood plain. 
Wherever there is an elevated stretch of land adjoining a 
body of water, such as a lake bluff, one is apt to.find excellent 
illustrations of the beginning of a ravine. Fig. z shows an 
embryonic ravine of a type that may be seen frequently along 
the clay bluffs between Evanston and Waukegan. A ravine of 
this type is essentially a desert, so far as plant life is concerned. 



