252 NICHOLS: THE VEGETATION OF CONNECTICUT 
After a few years have passed, xerophytic shrubs appear, . - - 
and it is not long until xerophytic or semi-xerophytic thickets 
prevail in place of the former mesophytic undershrubs. The last 
of the mesophytes to die are trees, because they are longer-lived 
than herbs and shrubs, and also because their roots reach down to 
the moisture’; but eventually these too give way to relatively 
xerophytic species. In Connecticut, the changes are not 80 
radical; in fact, a bluff forest may be scarcely less mesophytic 
than a ravine forest. This is not surprising when it is 
considered that the climax formation in this region (that is, the 
most mesophytic type of vegetation which is capable of develop- 
ment on uplands) is very nearly as mesophytic as the climax 
association (termed by Cowles a “temporary climax’’) of ravines. 
In the Chicago region, on the other hand, the contrast between 
the mesophytic ravine forests and the xero-mesophytic climax 
forests on uplands is very pronounced. 
The most striking difference between a bluff forest (FIG. 5) 
and a ravine forest is seen in the greater abundance of relatively 
intolerant trees. The undergrowth also, while it may contain 
any of the characteristic ravine species, includes many forms which 
ordinarily do not thrive under the shadier ravine conditions. 
On bluffs in unconsolidated rock, especially on clay and till, the 
. soil moisture relations usually favor the continuance of a mes0- 
phytic flora. Near the mouth of the Windsor ravine, to select 4 
concrete example, along the bluffs which border the Farmington | 
Valley, common trees are Juglans cinerea, Tilia americana, Betula 
alba papyrifera, Ulmus americana, Platanus occidentalis, Cary4 
cordiformis, Quercus rubra, Ostrya virginiana, and Carpinus carolin- 
tana. Along with these occur the trees of the ravine forest—the 
sugar maple, white ash, tulip and yellow birch, and to a less extent 
the hemlock. 
The undergrowth of moist valley forests is particularly rich 
in spring-flowering species. Among the herbaceous plants chat- 
acteristic of such habitats may be mentioned the following: 
Aspidium noveboracense Botrychium virginianum 
Asplenium Filix-femina Oakesia sessilifolia 
Adiantum pedatum Allium tricoccum 
Osmunda Claytoniana Erythronium americanum 
