g2 BOTANICAL GAZETTE [ FEBRUARY 
widening ravine at Beverly hills; the vegetation is much less 
luxuriant than that shown in the young ravine of fig. 2. 
After a few years have passed, xerophytic shrubs appear on 
the bluff in place of the witch hazel and its associates. And it 
is not long until xerophytic or semi-xerophytic thickets prevail, 

Fic. 4.—Side of a cafion in the St. Peters sandstone at Starved rock. Herbaceous 
shade vegetation on the precipitous slopes. 
in place of the former mesophytic undershrubs. Among the 
more characteristic of these shrubs are the hop tree (Prelea trifo- 
liata), bittersweet ( Celastrus scandens), sumachs (Rhus typhina 
and R. glabra), choke cherry (Prunus Virginiana), nine-bark 
(Physocarpus opulifolius), wild crab (Pyrus coronaria). Two 
small trees are common on stream bluffs, the service berry 
(Amelanchier Canadensis) and the hop hornbeam ( Osétrya Virgin- 
ica); this last species is perhaps the chief character tree of river 
inten ee: 
