454 Part IV. Chapter 2. 
and its replacement by the short leaf pine, Pinus mitıs (= P. echinata) 
is sufficient to characterize it. The line which demarcates the two regions, 
therefore, is the northern boundary of Pinus palustris. Besides it is inland, 
and physiographically it covers a territory entirely different in character from 
the coastal plain. It is a district which owes its physiographic condition to 
the Mississippi River, which in its meanders has swung several times across 
its flood plain giving rise to freshwater alluvial deposits, or bow lakes, nume- 
rous bayous, freshwater swamps and marshy plains. The type of forest and 
vegetation has been modified accordingly and although many species of the 
Gulf coast are present yet the character of the association of species rather 
than the constitution of the primary formation show a considerable modification. 
ı. Lower Alluvial Forest land. 
The alluvial bottom land of the Mississippi Valley is covered by mighty 
forests. In the lowest levels with the surface soil, constantly under water are 
found the cypress swamps where Tarodium distichum is supreme. On slightly 
elevated ground Ouercus virginiana, O. laurifolia, Q. aquatica draped with 
Tillandsia usneoides occur, and under the shade of the older larger trees a 
growth of secondary species: Ouercus terana, Fraxinus viridis (= F. lanceo- 
lata), Salix nigra, Crataegus viridis, Ilex verticillata, I. decidua, Forestiera 
acumina’a'). The trees in the shallow portions of these swamps support cer- 
tain lianas: Smilar bona-nox, S. pseudo-china, Clematis crispa. Certain of 
these sloughs are almost exclusively occupied by Leitneria floridana & plant 
found nowhere else except in coastal Florida, its northern extension 
being due to the swampy character of much of the land along the general 
course of the Mississippi River in southern Missouri, northern Arkansas as 
well as further toward the Gulf). 
Cypress Swamp Formation. The cypress swamps of southeastern Missouri 
are typically developed about the Saint Francis River. Here in deep swamps 
occur Taxodium distichum, thickets of Planera aquatica (in soil never covered 
with a great depth of water) and the rare and monotypic Leifneria floridana 
with Polygonum densiflorum, which seems to be the first in order of succession 
of those plants which obtain a foothold in the soil and lift themselves out of 
the water®). A large part of the river bottom is covered with Myriophyllum, 
Ceratophyllum, Potamogeton and Cabomba and the consequent filling up of the 
channel enables Polygonum densiflorum and Zizaniopsis miliacea to gIOW. 
In many quiet places the water is covered with Asolla caroliniana, Lemna 
1) MoHR, Cart: Die Wälder der Alluvialregion des Mississippi in den Staaten Louisiana, 
Mississippi und Arkansas. Pharmaceutische Rundschau XIII: 14. 30. Jan. 1895. 
2) BusH, B. F.: Notes on a List of Plants collected in ae Missouri in 1893. Fifth 
Report Missouri Botanical Garden 1894: 139—153; TRELEASE, WIL : Leitneria floridana do. 
Sixth Report 1895: 65—90. See also TRELEASE, WM.: Garden ey Forest X (1897) 376. 
3) COULTER, SAMUEL M.: An ecological Comparison of some typical swamp Areas. ı5th Re- 
port Missouri Botanical Garden p. 54. 
