216 Part III. Chapter 3. 
*Ipomoea acetosaefolia R. & S. | Lippia (Phyla) nodiflora L. . 
ER. Pes-caprae L. | *Sesuvium portulacastrum L. 
**Lithophila (Philoxerus) vermiculataL. | Sabal glabra Sarg. (= S. Adansonii 
Chrysoma pauciflosculosa Michx. | Guerns). 
Uniola paniculata L. | Serenoa serrulata Hook. f. (= Sabal 
Iva imbricata Walt. | serrulata R. & S.) 
The soil of the delta itself represents that of the most recent formations 
of the southern coastal region. The “passes” of the Mississippi River are 
broad channels of water separated from the waters of the Gulf by an irregular 
and frequently very narrow strip of land of river deposit. Enormous quantities 
of silt must be sorted and arranged by tidal and current action in the for- 
mation of perhaps the newest land of the continent. Phragmites, Vigna and 
Spartina form associations. Phragmites occupies the higher levels, Spartina 
makes dense matted growths in the swampy ground of the lower levels. Vigna 
clambers on the canes and forms an almost impenetrable thicket, while occa- 
sional trees of Salix, Cissus bipinnata and Ampelopsis arborea occur along 
the bank. The muck marsh islands about the mouth of the Mississippi are 
composed of a very fine black alluvium with surface low-lying and flat. The 
flora is limited to .a few species usually in two associations. The grasses 
Spartina patens, S. stricta and Distichlis maritima (= D. spicata) form one 
association, while succulents Batis maritima of tropic distribution, Salicornia 
Bigelovii and S. ambigua form the other. Avicennia nitida also is found here. 
These muck islands may be converted into sand islands by receiving a supply 
of sand, which sometimes reaches a thickness enough to support Ayris sero- 
tina, Utricularia subulata, Oldenlandıa uniflora, Siphonychia ( Odontonychia) 
corymbosa, Polypremum procumbens, Gratiola subulata (= Sophronanthe hispida 
and Diodia virginiana. The flora of these islands are just as old, as the soil 
deposits on which they are found, the muck marsh flora being perhaps much 
older, as a floristic element. If the sand of the sand islands becomes thin by 
drifting away, muck marsh conditions may be restored by the appearance of 
Batis and Salicornia. 
The sand plain floristically has three leading types determined by the 
physiographic age of the land. The youngest is the sand spit, which is a 
low Iying extent of sand, hot, brilliantly lighted, wind swept and sea inundated 
in heavy weather. Mollugo verticillata, Panicum repens, P. halophilum, Tva 
imbricata, Serenoa serrulata, Scirpus americanus, Cyperus cylindrieus, Diodıa 
teres, Syntherisma fimbriatum, S. filiforme, Cenchrus incertus, C. tribuloides, 
Euphorbia (Chamaesyce) cordifolia and Physalıs angustifolia represent the flora 
covering of the basins, low dunes and level reaches of the sand spit plain. 
The second type of sand plain is the open grass plain covered with her- 
baceous plants and such grasses as Chaetochloa magna, Umiola paniculata and 
the slender vines Vigna glabra, Clitoria martana, associated with Chamae“ 
crista littoralis, Gerardia purpurea and Croton maritimus (= C: punctatus): 
The sand plain, however, culminates in the forests of Pinus palustris = 
PR 
