276 BOTANICAL GAZETTE [ocToBER 
As a whole, the bluff vegetation is made up of light-requiring 
species. The prevailing forest trees are among the least shade- 
enduring kinds to be found in the region. Such trees never crowd 
together to form the dense type of woods common on the floodplain; 
but, like the black oak woods, or like the openings of bur oak west 
of Ann Arbor, the trees stand far enough apart to permit an abundant 
ars in 
round; 
Fic. 4.—Washed slope in juniper-heath stage; the ground juniper appe 
patches in the foreground, with red cedar forming a dense grove in the backg 
near Rawsonville, Michigan. 
growth of smaller vegetation to spring up in the woods. Also there 
is less tendency to growth in mixture. The sumac and junipers are 
gregarious, and there is not the variety of trees in the oak woods that 
there is in case of the more mesophytic kinds. The tendency of the 
black oak group to occur on sands, and of the hickories to occu! “ 
clays, are among the most constant relations which societies have 
been found to bear to soil types. 
