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peared. Near the Illinois river there are some rather extensive sand 

 fields occupied by a forest characterized particularly by bur oak and 

 white oak, with several other arborescent species, such as red oak, 

 Quercus rubra, elm, Ulmus americana, hackberry, Celtis occidentalis, 

 and white ash, Fraxinus auiericana. This probably represents the 

 complete succession, the beginning of which has been indicated above. 

 Intermediate stages, however, have not been observed. 



In the Oquawka area the succession is found only on the long 

 dunes nearest the river. The first indication of it is given by SUenc 

 stellata, Polygonatum commutatum, and Psedera quinquefolia, which 

 are followed by a number of additional species, including several 

 trees. The whole leads to the highest type of mesophytic forest (PL 

 XX, Fig. 2, background) that occurs on the sand deposits. 



The succession is best seen along the dune nearest the river, north 

 of the town of Oquawka, and may be traced through various stages 

 from north to south for a distance of about 1.5 miles (2 km.). This 

 dune has a maximum height of about 100 feet (30 m.), indicating a 

 very strong and continued wind action at some time in the past. It 

 is now completely covered with trees, and the surface layers of sand 

 are well mixed with organic matter. At the north end a bayou of 

 the Mississippi lies at its base, and the margin of the water is marked 

 by a line of elms and willows, with Rumex verticillatus, Physostegia 

 virginiana, and other species of hydrophytic tendencies. Bqnisetum 

 hyeniale is the only one of these which extends much above the water- 

 level, where it mingles with the usual sand-dune species. Along the 

 north end of this ridge the prevailing trees are Quercus velutina and 

 Quercus marilandica, with occasional trees of Quercus rubra, espe- 

 cially on the lower part of the slope. Besides the pioneer herbaceous 

 species mentioned above, there are also Strophostyles helvola, Mo- 

 aurda Ustulosa, Aquilegia canadensis, and Vitis vulpina. Somewhat 

 farther toward the south Juglans nigra appears near the base of the 

 hill not far above water-level; farther along it extends higher and 

 even appears at the top of the dune. Cercis canadensis is usually 

 found with it. In the same way the river birch, Betula nigra, the elm, 

 Ulnius americana, the green ash, Fraxinus pennsylvanica, var. lance- 

 olata, and finally the soft maple, Acer saccharinum, appear first at 

 the bottom of the dune and as mesophytic conditions increase toward 

 the southward extend higher and higher above water-level, until they 

 finally appear at the top. Each one of these species is more moisture- 

 loving than its predecessors, until the climax is reached in the soft 

 maple, a characteristic tree of river-bottom swamps, here growing 

 many feet above the water. 



