152 



laria, Caulophyllum. PodophyUiini, Dentaria Jaciniata, Jlola- 

 scabriuscula. GenDiinin, maculatuui, Impatiens aiirea, Oxalis 

 racemosa, Phlox divaricata, HydropJiyllum viri^inianum, Scutel- 

 laria versicolor, Agastache. Cainpanula amcricana. 



The black oak association is remarkable for at least two 

 things, viz : that commonly the oak is the only notable tree species, 

 and further that wherever dry, barren, or eminently unfavor- 

 able land surfaces are found, there it will be certain to grow. 

 These barren soils are to be found in three well-marked and 

 seemingly quite different topographic areas : first, on the ele- 

 vated summit ridges of the Niagara mounds ; second, on the 

 equally dry and rocky brows of the Apple river and Mississippi 

 river bluffs ; third, in the dune region adjacent to the 

 Mississippi on sand prairie in the southwestern part of Jo 

 Daviess county. A height of 60 feet and a diameter of 2 

 feet will mark the largest growths. They are generally scrawny, 

 often hollow, and only in young trees thriftly in appearance. 

 The most thrifty specimens are found on the tops of the mounds 

 and in spots of some con"Lparative richness of soil. May it 

 not be true that the oak grows in pure sand oif the dune or 

 on the dry rocky knoll because it there finds little or no com- 

 petition, and not because it would not do better on a richer 

 soil if it were to be given possession. Seemingly an isolated 

 species it consorts poorly with other ])lant growths of tree pro- 

 portions. 



With the black oak are to be found a very few tree species, 

 most prominent among them an occasional great-toothed poplar 

 (Popuhis grandidentata) , June berry (Amelanchier canadensis,) 

 and several species of Crataegus. The shrubby growth is mostly 

 hazel, Jersey tea, and white dogwood (Coruns pamculata). 

 Among herbaceous species a few only are conspicuous: various 

 species of Desmodium and Lespedeza, Viola pcdata, Dodecatheon, 

 Lithospermum cancsens, Isanthus, Hedeoma, hispda, Gerardia 

 laevigata, Liatris scariosa, Kuhnia, Aster limirifoliiis, A. ptarmi- 

 coides. The sand dune flora of this oak association has some 

 interesting additions to the above, notably Opuntia, Rhus cana- 

 densis, Synthyris, Krigia virginiana, Tcphrosia virginiana and 



