173 



croachin^ upon the l)ottoms of the Illinois River. Besides the 

 hlack-jack oak, which constitutes, liy rough estimate, fifty per- 

 cent of the forest, there is ahout thirty-Hve percent of hlack 

 oak, Qiicreiis rcliitiiid, and hfteen percent of hi(;kory, Jlicon'd 

 iiui-ninir/iii. These three are the only arliorescent species of the 

 black-jack tiniher, and in s(Mne places Init one of them ((^>iiciri<f< 

 iiiiiriihiiidicK ) 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 produci'.ig fruit. The underbrush con- 

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

 with occasional clumps of lllim^ iinnHdlicii. Other shriil)l)y 

 species of less prominence occur, such as Anior/ilKi ctnii'sci'iis and 

 Su/i.r frisfl.s. Since the ecology of the black-jack as.sociation, 

 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 shrul>by flora of the 

 two are very similar. Of the species obser\ed on the prairie, 

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

 were Spdiiiud ci/ddsdroidcs, Sfljia sjitnird. ( 'itldiidirilfd lid(<i'it'(iHd, 

 Sfeiloillu///ns atpilldris. Fiijdihis (Icltnnlcs^ AciT Xi'(Jii iiihi. ('risfd- 

 telld Jdlld'nii, I'opdilis (llldtdfd. (ili'ditsdt f ridfinifhos, Li-sqdri-cl l(( 



spaf/nildfd. Acenites rir/ilifiafd, Hin-dcidiu /oid/ipi/dui. and E(jdi- 

 xpfdid rol)i(sfuhi. This number would probably be reduced by 

 extended observation. The principal distinction between the 

 two floras is the poorer quantitative development of the liunch- 

 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-fonniug species are Paii- 

 d'lnii roijitdtiDH, Tricdspis scs/crididcs, Ki-(d/j'(ixf/s frd'/dx/cs, I'dsjid- 

 him scfdi'finii. and Aid/i-opni/dii furcdtds. and the bunches are 

 few and widely scattered. This difference in development in 

 "he two formations is probably due entirely to the amount of 

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



