182 BOTANICAL GAZETTE [MARCH 
maples and beeches, and this change is now occurring in some 
places. The mesophytic stage here also is not permanent, 
though it may endure for a long period. 
Clay bluffs along an eroding coast are subject to considera- 
ble change involving the rapid destruction of upland vegetations. 
The changes, too, are so rapid that practically no vegetation can 
develop on the bluff slopes. If the erosive activity of the lake 
ceases, there soon appears a vegetation of xerophytic herbs, fol- 
lowed by xerophytic shrubs and trees in which conifers play a 
large part. There is a notable resemblance between the flora of 
the clay bluff along the lake shores and the flora of the sand 
dunes, and also the flora of rock bluffs along rivers, while the 
resemblance is less close to the flora of clay bluffs along rivers, 
showing that soil conditions may often be less important than 
conditions of aerial exposure. 
The dune vegetation, presented in dean elsewhere, is sum- 
marized in this present paper. Nothing need be said in the way 
of further summary except to remark that dunes, like all other 
topographic forms in our climate, may ultimately develop a 
mesophytic forest, though the stages are far slower than in most 
of the other series. 
THE UNIVERSITY OF CHICAGO. 

