172 ILLINOIS STATE ACADEMY OF SCIENCE 



and Ulmus are added on this lower bank. Somewhat far- 

 ther up the bank Ostrya virginiana, Juniperus virginiana, 

 Celtic occidentalis, Gleditsia triacanthos, are present. 

 Still farther up are the oak woods. Of course these species 

 are not in zonation, as their mentioning might indicate. 

 More or less intermingling takes place until the area of the 

 oaks is reached. Here, on and about the sandy top of the 

 bluffs, are also such species as Melilotus alba, Verbena stricta, 

 Lespedeza capitata, Strophostyles helvola, Liatris scariosa, 

 Verbena angustifolia, Achillea millefolium, Chenopodium al- 

 bum, Physalis sp. These herbaceous forms are practically 

 all those of dry sandy sites, the so-called waste places. Af- 

 finities with the prairie vegetation are to be seen in such 

 as Verbena stricta and Liatris scariosa. More than half 

 the species mentioned belong to the weed class. Melilotus 

 is of general occurrence throughout North America, except 

 in the far north, on sites of this character. The upper layer 

 of this sandy soil on the top of these bluffs appears, hence, 

 to be rather dry, while the deeper soil layers contain much 

 more moisture, at least as judged by the vegetation sup- 

 ported. Upon one of the sandstone cliffs occurring along 

 these bluffs, the small cliffs known locally as "buttes," Pinus 

 strobus occurs sparingly at the verge. Juniperus virgini- 

 ana, Quercus alba, Q. ellipsoidallis, Q. velutina, small 

 Populus grandidentata, with Carpinus caroliniana and Py- 

 rus melanocarpa were also present on the cliff top. In the 

 oak woods farther back from the river, where the stand 

 of trees is much denser and the soil conditions much better, 

 where in short a later stage of succession has been attained, 

 such an assemblage as the following is representative: 

 Quercus alba, Q. rubra, Q. velutina, Q. ellipsoidalis, Tilia 

 americana, Juniperus virginiana, Hicoria minima, H. ovata, 

 Fraxinus americana, Ulmus pubescens, Prunus serotina. 

 In the undergrowth occur Ostrya virginiana, Cornus pani- 

 culata, Xanthoxylon americanum, and so on. The succes- 

 sion has passed in large part from the oak woods stage 

 of the top of the bluffs but still retains many traces of the 

 former. Considerable habitat differences within small areas 

 are here a feature of this. 



