286 ILLINOIS ACADEMY OF SCIENCE 



elm (Ulmiis americana) white ash (Fraxinus americana) 

 and wild black cherry (Priinus serotina). In some places 

 this association is scarcely distinguishable from the next 

 but in other cases, as in section 28, there are quite exten- 

 sive and well marked areas of it. 



The mixed hillside association (34, 34.1, 34.2 and 34.3). 

 The forest that occupies the yellow silt loam on the slopes 

 and in the ravines is transitional in its nature. It really 

 consists of several distinct forest associations but the rep- 

 resentations of the separate associations are often so lim- 

 ited in extent that each one includes only a few individual 

 trees. For this reason it is thought best to treat it here as 

 a mixed association and without any attempt to indicate 

 an}' particular species as dominant, since different species 

 are dominant in different parts of the forest. The species 

 of trees in this forest vary from those of the mesoxero- 

 phytic association described above, such as black, white 

 and chestnut oaks (Querciis velutina, Q. alba and Q. 

 primis) and the shagbark and pignut hickories (Carya 

 ova fa and C. cordifonnis) and sometimes red cedar 

 (Juniperus virginiana) on the higher parts of the slope, 

 through the group of species characteristic of more meso- 

 phytic forests such as hard maple (Acer saccharum), 

 beach (Facjus gr(indifolia), red, yellow and shingle oaks 

 (Quercns rubra, Q. imbricaria and Q. muhlenbergii) , 

 basswood (Tilia americana), red elm (Ulmus fiilvaj, 

 ironwood (Ostrya. firginiana), red bud (Cercis cana- 

 densis) and white ash (Fraxinus americana) in the 

 intermediate positions, to the species more characteristic 

 of hydrophytic forests such as red ash (Fraxinus penn- 

 sylvanica), American elm (Ulmus americana), walnut 

 (Juglans nigra), sycamore (Platanus occidentalis), honey 

 locust (Gleditsia triacanthos) and sometimes black wil- 

 low (Salix nigra) or occasionally glaucous willow (Salix 

 discolor) on the lower parts of the slopes and in the bot- 

 toms of the valleys. This type of forest is more extensive 

 than any other in this region, for the reason that the land 

 on which it grows is mostly too steep or too hilly for culti- 

 vation. Certain patches of this type, too, are the only 

 forests in the region that are not persistently pastured. 

 Xo forests were found that had never been pastured, but 

 certain areas of the mixed hillside association are appar- 

 ently pastured only when the adjoining fields are pastured 



