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croaching upon the bottoms of the Illinois River. Besides the 

 black-jack oak, which constitutes, by rough estimate, fifty per- 

 cent of the forest, there is about thirty-five percent of black 

 oak, Quercus velutina, and fifteen percent of hickory, Hicoria 

 microcarpa. These three are the only arborescent species of the 

 black-jack timber, and in some places but one of them (Quercus 

 marylandica ) is present, The trees seldom exceed a foot in di- 

 ameter, and they are generally very crooked, gnarly, and full 

 of dead branches. The hickory is nearly always sterile, only 

 the very largest trees producing fruit. The underbrush con- 

 sists mainly of young trees of hickory and the two oaks, 

 with occasional clumps of Rhus aromatica. Other shrubby 

 species of less prominence occur, such as Amorpha canescens and 

 Salix tristis. Since the ecology of the black-jack association, 

 at least during its early stages, differs from that of the original 

 bunch-grass association only in the smaller amount of light re- 

 ceived by its plants, the herbaceous and shrubby flora of the 

 two are very similar. Of the species observed on the prairie, 

 all but thirteen were also found in the black-jack forest. These 

 were Spartina cynosuroides, Stipa spartea, Calamovilfa /<>//<// folia, 

 Stenophyllus capillaris, Populus deltoides, Acer Negundo, Crista- 

 tella Jamesii, Populus dilatata, Gleditsia triacanthos, Lesquerella 

 spathulata, Acerates viridiflora, Hieracium longipilum, and Equi- 

 setum robustum. This number would probably be reduced by 

 extended observation. The principal distinction between the 

 two floras is the poorer quantitative development of the bunch- 

 grasses in the black-jack association, and a corresponding in- 

 crease in the representation of the other species. In the edge 

 of the woods, which differs the least from the prairie both in 

 age and in ecology, the bunch-grasses are well developed, and 

 the majority of the species may be found. In the older and 

 more densely shaded parts the bunch-forming species are Pan- 

 icum cognatum, Tricuspis seslerioides, Eragrostis trichodes, Paspa- 

 lum setaceum, and Andropogon furcatus, and the bunches are 

 few and widely scattered. This difference in development in 

 the two formations is probably due entirely to the amount of 

 light. The remainder of the flora is characterized by the great- 



