FORESTRY SURVEY 241 



Floristic Geography. 



Floristic aspects of plant geography emphasize the 

 peculiarities of distribution of particular species of 

 plants. Certain other interesting floristic features are 

 presented in Cumberland county. 



A north-south floristic transition results from the fact 

 that migration of trees has proceeded upstream along the 

 valleys of the generally southward-flowing streams, and 

 that certain tree species are here nearly at the upper limit 

 of their distribution along the Embarrass drainage system. 

 The sweet gum (Liquidamhar sfi/racifiua) formerly grew 

 on the Embarrass near the southern edge of the county. 

 The writer knows of no more northerly station for it in 

 Illinois. The mulberry (Moms nihraj, sassafras (Sassa- 

 fras sassafras), persimmon (Diospi/ros virginiana), 

 cofl^ee tree (Gi/mnocladiis dioica), dogwood (Cornus 

 fiorida), and papaw (Asimina triloba), though all range 

 considerably to the north, are increasingly abundant and 

 grow to larger size southward. 



Pin oak (Quercus pahisfris), post oak (^Quercus minorj, 

 and the river birch (Betula nigra) are common in Cum- 

 berland county, but only post oak is known by the writer 

 to occur in Coles county, just to the north, and that very 

 rarely. The black-jack oak (Q. marilandica) occurs 

 rather infrequently in Cumberland county though it is 

 common fifty miles south in clay soil, and is abundant in 

 the sandy parts of the Illinois river valley. Probably the 

 absence of the three oaks mentioned from the area just 

 north of Cumberland county is due to the difference in 

 soils upon the two sides of the moraine, not that these 

 species could not grow in the better soil on the northern 

 side, but they probably can not compete successfully with 

 the other trees which grow there. The difference in soil 

 is well indicated by the presence, in the lower Illinois 

 glaciation, of the two herbs. Ambrosia bidentata and 

 Plan f ago aristata, which appear most commonly as road- 

 side weeds, though originally they were probably mem- 

 bers of primitive (pioneer) prairie associations. 



An east-west floristic transition results from the west- 

 ward migration of trees, as the forest encroached upon the 

 prairie region. Certain tree species are well established 

 along the valleys all over Illinois, but certain others, as 



