288 ILLINOIS ACADEMY OF SCIENCE 



dominant trees are the basswood (Tilia americana) and 

 the white elm (Ulmus americana). Along with these occur 

 hard maple (Acer saccharum), walnut (Juglans nigra), 

 yellow oak (Qiiercus mulilenhergii), white and red ash 

 (Fraxinus ainericana and F. pennsylvanica) , and hack- 

 berry (Celtis occidentalu). 



Hydeophytic Forest Associations. 



TJie elm-sycamore-maple association (41, 41.1, 41.2 

 and 41.3). This is the hydrophytic forest that formerly 

 occupied most of the mixed loam or bottomland soil. A 

 great deal of this soil has been cleared but a number of 

 representative bottomland forests still remain especially 

 as narrow strips along the river. The dominant trees of 

 this forest are the white elm (Ulmus americana), the 

 sycamore (Platanus occidenfalis) and the soft maple 

 (Acer saccharinum). Along with these occur hackberry 

 (Celtis occidentalis), box elder (Acer negundo), green 

 ash (Fraxinus pennsylvanica var. lanceolata), bur-oak 

 (Quercus macrocarpa), walnut (Juglans nigra) honey 

 locust (Gleditsia triacanthos ) , black maple (Acer sac- 

 charum var. nigrum) and cottonwood (Populus del- 

 toides). 



The cotto?iwood-icilloiv association (43). This hydro- 

 phytic association is represented in several places along 

 the river. In most places it consists almost exclusively of 

 cottonwood (Popiilus deltoides) and black willow (Salix 

 7iigra), with the sandbar willow (Salix longifolia) occur- 

 ring where the river is depositing sand. These sand de- 

 posits are frequently submerged and most plants are un- 

 able to grow on them at all, but the sandbar willow does 

 not suffer from the water. It has to contend rather with 

 biotic factors, since it is usually badly infested with wil- 

 low-cone galls and often is completely covered with a spe- 

 cies of dodder. 



The cottonicood-icilloiD slough association (51). This 

 association is represented only by a small patch in the 

 southern part of section 9. Here an old abandoned 

 gravel-pit has as its center a patch of cattails (Typha 

 latifolia) which is surrounded by an association of young 

 trees and shrubs of the glaucous and black willows (Salix 

 discolor and S. nigra), cottonwood (Populus deltoides) 

 and a few sycamores (Platanus occidentalis). 



