248 PLANT RELATIONS. 



very interesting modification. It sends up its rosette of 

 large and very active leaves during the vernal season, and 

 when these have disappeared the flowers are developed in 

 the forest shade. The significance of this is that while 

 the leaves must have the light for their work, the flowers 

 can develop jnst as well in the shade. 



As in the case of thickets, deciduous forests may be 

 pure or mixed. A very common type of pure forest is the 

 beech forest, which is a characteristic dark forest. The 

 wide-spreading branches of neighboring beeches overlap 

 each other, so as to form dense shade. As a consequence, 

 in a pure beech forest there is little or no undergrowth ; in 

 fact, no lower strata of vegetation until the lowest ones are 

 reached, made up of grasses and mosses. Another type of 

 pure forest, which belongs to the drier regions, is the oak 

 forest, which forms a sharp contrast to the beech, in that 

 it is a light forest, permitting access of light for lower 

 strata of plants. Hence in such a forest there is usually more 

 or less undergrowth, consisting of shrubs, etc., which may 

 develop regular thickets. The typical American deciduous 

 forest, however, is the great mixed forest, made up of many 

 varieties of trees, such as beech, oak, elm, walnut, hickory, 

 gum, maple, etc. 



The deciduous forests may be roughly grouped as up- 

 land and flood-plain forests, the former being less luxuriant 

 and containing fewer types, the latter being the highest ex- 

 pression of forest development in its region. A few general 

 illustrations may be given as follows : 



In northern Illinois the upland forest is mostly made 

 up of three forms, white and red oaks and shellbark hick- 

 ory ; while the flood-plain forest contains twenty to twenty- 

 five tree forms, prominent among which are the elms (white 

 and slippery), linden (basswood), cottonwood, ash, silver 

 maple, box elder, walnut, and willows (see Fig. 211). 



Farther south, from central Illinois, Indiana, and Ohio 

 southward, as well as in the Alleghanies, the flood-plain for- 



