No. 17] FLOWERING PLANTS AND FERNS 37 
The following are common clinging to limestone bluffs: 
Camptosorus rhizophyllus Saxifraga Virginiensis 
Woodsia obtusa Dentaria laciniata 
Tris cristata. Anemonella thalictroides 
Flatwoods.—This region, as the name implies, presents 
usually a low lying flat topography, though in certain parts the 
surface becomes rolling and even hilly. The characteristic 
feature, however, is its flatness, which has caused it to be liken- 
ed to a broad river valley This region extends as a belt or 
zone from three to fifteen miles wide north and south aleng 
the west edge of Pontotoe Ridge from the line of Tennessee 
to the point of the Ridge. South cf Houston, Chickasaw Coun- 
ty, the Flatwoods skirt the western edge of the Cretaceous 
prairie region. 
The soil of this region is prevailingly a heavy, tenaceous, 
dark gray clay, with a subsoil of gray joint clay. The drain- 
age is usvally not good, so that the soil,except in dry years, is 
wet and cold, and more or less acid. This heavy type of soil 
shades in places into a lighter, sandier soil, which lies higher 
and is better drained. Both types of soil are lacking in lime 
and are deficient in other elements of plant food. The close 
texture of the heavy clay soil makes it very tenaceous of 
moisture, so that it is either too wet to favor plant growth, or 
when dry becomes too hard and compact. So that the region 
is not one of rich growth and those species present are usually 
of xerophytic habit, which fits them for the extreme alternate 
conditions of sterile, water-logged, acid soil, and dry soil of 
stony hardness. 
These conditions are reflected in the tree and shrub growth 
of the region, which consists chiefiy of pine (Pinus mitis and 
Pinus taeda) and of oaks of a few xerophytie species, as black 
jack, post oak, and Spanish oak. These usually form open 
forests, with here and there on the lower flats scattered growth 
of haws (Crataegus, several species) and deciduous helly. 
Since soil and topographic features cf the Flatwoods shade 
into those of the larger region lying to the west—and next to 
be considered—the floristic features of the two merge. Hence 
