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 so 

 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 meso-!- 

 phytic flora. Near the mouth of the Windsor ravine, to select a 

 concrete example, along the bluffs which border the Farmington 

 Valley, common trees are Juglans cinerea, Tilia americana, Betula 

 alba papyrifera, Ulmus americana, Platamis occidentalis, Carya 

 cordiformis, Quercus rubra, Ostrya virginiana, and Carpinus carolin- 

 iana. 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 char- 

 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 



