LAKE BLUFF, RAVINE, AND RIVER VALLEY 275 



gold come early in the wet areas. Spring beauty often covers 

 the ground completely, and later the phlox (Phlox divaricata) 

 may cover acres with its bloom. Bloodroot, bedstraw, cheveril 

 (Fig. 421), blue cohosh, dogtooth violet, fringed loosestrife (Fig. 

 422), geranium, wild ginger, honewort (Fig. 423), leeks and 

 onions, false mermaid weed, cow parsnip (Fig. 424), Solomon's 

 seal, both true and false, sweet cicely, spring cress of several 

 species (Fig. 362), trillium, . toothwort (Fig. 55), violets, and 

 waterleaf are the common members. 



It is interesting to note the arrangement of these flood-plain 

 zones on an island in midstream. Some shift of current or some 

 obstruction causes the sediment held by the river to deposit, and 

 so a mud barrier forms in midstream, a patch of flood plain dis- 

 connected from the shore. Such an island grows on its down- 

 stream side because the current is checked by the obstruction 

 and the deposit is in the quiet waters below it. Vegetation, 

 therefore, appears on its upper end as soon as this portion dries 

 out sufficiently to permit plant growth. For the same reason, 

 the flood plain forest develops here, and successive zones extend 

 toward the lower end. Islands in a lake or pond have their 

 zones arranged more or less in concentric rings in contrast to 

 the longitudinal zones of the river island. 



There is usually a marked contrast between the vegetation of 

 the river valley and that of the bordering hills. We have 

 already noted above the vegetation of the rock hills. Customa- 

 rily the hills that border the flood plain bear the usual white oak, 

 red oak-hickory forest, which has been considered in chapter x. 



In most respects the animal life of the flood-plain forest is 

 very like that of the climax beech-maple forest, though the 

 forms are not as numerous, as the annual inundation prevents 

 the permanent residence of many animals. The short-tailed 

 shrew (Fig. 425), white-footed deer mouse (Fig. 287), and com- 

 mon mole (Fig. 286) are usually present. The same beetles are 

 present on the ground and in the rotting logs. The mollusks 

 are similar though not as numerous. 



