174 ILLINOIS STATE ACADEMY OF SCIENCE 



dissemination of the pine seed has been for some time 

 past and is now so vigorous, however, that it appears to 

 the writer to account, in connection with the other matters 

 recounted here, for the reversal found of the usual course 

 of succession. Here, instead of the pine woods being in- 

 vaded by the oaks, as usually takes place in the eastern 

 United States, the oak woods are unquestionably being in- 

 vaded by the white pine along the oak woods-white pine 

 border zone in the territory of the dense white pine stand. 



Let us consider now a few localities of the region that are 

 representative of the climax and of certain plant assem- 

 blages that are on the other hand removed somewhat from 

 the regular course of succession. In the big bend of the 

 Rock at Grand Detour some herbaceous forms are of in- 

 terest. This flat, consisting mainly of the terrace soil 

 yellow-gray sandy loam over gravel, with some parts of 

 the bottomland soil mixed loam, and a small area of sand- 

 stone rock outcrop, formerly bore a mesophytic woodland 

 with oaks, walnuts, and so on, of large size. The whole 

 area is now under cultivation, except for the part compris- 

 ing an abandoned channel of an artificial mill stream, and 

 only a border zone of streamside vegetation is present along 

 a portion of the Rock. Some of the herbs in the stream- 

 side border and in the cultivated fields are Ambrosia trifida, 

 which is very prominent, A. artemisiifolia, A. ludoviciana, 

 Oenothera biennis, Convolulus sepium, Acnida tuberculata, 

 Silphium perfoliatum, Polygonum pennsylvanicum, Verno- 

 nia fasciculata, Brassica sinapistrum, Bidens sp., with many 

 other forms. A large number of the grasses of the county are 

 to be found here as well. Here, in a cultivated area, as 

 in the so-called waste area of the sandy bluff tops west of 

 Grand Detour, prairie forms (such as Silphium perfoliatum 

 and Vernonia fasciculata) and weed forms have found a 

 habitat suitable for their establishment. 



The McCormack woods on the east shore of the Rock 

 north of Byron are of great interest. They comprise nearly 

 one square mile, and several parts of the area illustrate the 

 climax form of the Rock River woodland region. One rea- 

 son for this is unquestionably the fact that these woods 

 have been practically ungrazed for some time. A dozen or 



