125 



Seventy-one species may be regarded as typical of the forest 

 rather than the prairie, and of these, nineteen represent pioneers in 

 the succession of another, more mesophytic, type of forest, leaving 

 fifty-two to characterize the black oak association. 



The most distinctive feature of the flora is the large proportion of 

 perennial herbs. Thirty-nine species, or 75 per cent, of the total, be- 

 long in this general group. Contrasted with the same group in the 

 bunch-grass association, the chief difference is in the smaller number 

 of bushy forms, a type which seems to belong- primarily to the more 

 xerophytic prairie formation. The bushy perennials of the oak for- 

 est are almost without exception more abundant in and more charac- 

 teristic of the bunch-grass association. Callirhoc triaiigulata and 

 Asclepias tuberosa send up several ascending stems from a common 

 base ; Phlox bifida is divergently branched and may assume a rounded 

 shape; Hclianthcuunii 111a jus has erect stems which frequently grow 

 in clusters. Nearly all of these plants live also in the bunch- 

 grass association. By far the greatest number of species have erect, 

 simple or sparingly branched stems, without a large number of basal 

 leaves, growing singly or in small loose clusters. Pteris aqnilina 

 lives in large patches, spreading by its rhizomes, and Pedicidaris 

 canadensis has the same habit on a small scale. Fragaria virginiana, 

 var. illinocnsis, and Pofcntilla canadensis are also gregarious, spread- 

 ing by runners. Synthyris BuUii has a basal rosette of large subor- 

 bicular leaves which are closely appressed to the ground. 



A considerable number of species belonging to the interstitial 

 group of the prairie associations live also in the forest, but are lim- 

 ited usually to sunny places or the more open woods. Only four char- 

 acteristic species of the forest have this habit, and these plants are 

 neither common nor widely distributed. They are Anychia polygon- 

 oides, in the Hanover, Havana, and Oquawka areas, Casfilleja coc- 

 cinea, in the Winnebago area, Gnaphaliuni polycephahim, in the 

 Oquawka and Amboy areas, and Krigia virginica in the Ha^'ana area. 

 From an ecological standpoint, this group is of very slight importance. 



Shrubs are much more abundant in the forest than upon the 

 prairie. Rhus canadensis, var. illinoensis is the most abundant and 

 grows in irregular thickets, seldom exceeding two feet ( '^ dm.) in 

 height, but from 3-30 ft. (i-io m.) wide. It was not observed in 

 the Winnebago or Amboy areas, where its place is taken by the 

 equally abundant Salix tristis growing in thickets of the same gen- 

 eral structure. Ceanofhus aniericanus is found in all five areas and is 

 locally abundant. Rosa Jiuniilis is common in the Hano-^-er and 

 Winnebago areas. RJius glabra is occasional and a single individual 

 of Pynis americana w^as found in the Winnebago area. 



