178 ILLINOIS STATE ACADEMY OF SCIENCE 



Quercus is perhaps the chief tree. Fraxinus americana 

 and Hicoria minima are prominent. The undergrowth is 

 not remarkable, being about that found in the climax form 

 of the vegetation. Carpinus caroliniana is somewhat promi- 

 nent, however. Typical mesophytic and hydromesophytic 

 herbs abound, and this, with the fern display, consisting 

 of Osmundas, Aspleniums, Aspidiums, Cystopteris, Adian- 

 tum, Polypodium, with a profusion of mosses and lichens on 

 and about the moist sandstone rock wall forming the ac- 

 tual head of the ravine, are especially characteristic. 



The island vegetation is another very mesophytic form, 

 but of another sort. Omitting the streamside association 

 the islands generally bear a vegetation about as follows. 

 Ulmus americana and U. Pubescens may be considered the 

 chief trees. Fraxinus nigra, F. americana, Juglans nigra, 

 Celtis occidentalis, Juglans cinerea, Prunus serotina, Acer, 

 saccharum, A. nigrum, make up the other prominent spe- 

 cies. To these may be added such others of occasional oc- 

 currence as Tilia americana, Ailanthus glandulosa, Quercus 

 platanoides. Of course species like Acer saccharinum, Acer 

 negundo, Salix nigra, of the streamside association, are of- 

 ten present as well, back from the borders of the island. 



Consequently, from a comparison of the tree species alone, 

 it may be concluded that there is here, in places at least, a 

 telescoping of the climax form with the streamside associa- 

 tion, and, on most islands, certain special bottomland or 

 island features, such as the occurrences of Quercus plata- 

 noides, or a superabundance of Ulmus. The undergrowth 

 is very similar to that of the oak-maple climax, with, how- 

 ever, much more of liane growth. Often plants of hydro- 

 mesophytic are combined with plants of xero-mesophytic 

 tendencies, as when, for example, Cephalanthus occidentalis 

 and Crataegus occur near together. Shrubs such as Cornus 

 sericea, Sambucus canadensis, Staphylea trifoliata, are fre- 

 quent. The ground cover combines herbaceous form of 

 hydrophytic and mesophytic tendencies. 



In the Rock River woodland region, as well as one may 

 judge by observation alone, it appears that the main influ- 

 ence on the progression of the plant succession is the soil 

 moisture content. Of course this is the most obvious ele- 



