274 THE PLANT COVERING OF OCRACOKE ISLAND. 



Their borders are the favorite habitat of a characteristic malvaceous 

 plant, Kosteletzhya virginica, which has rather thin, pubescent leaves 

 and large rose-colored flowers. AVith it grow a species of Rnmex, 

 Ipomoea sagittata, Solidago semper virens, Cladium effusum (a stout 

 sedge with sharply saw-edged leaves), Panicum ivalteri, and, very 

 conspicuous where it occurs, Andropogon glomeratus {A. macrourus). 

 In the shallow water of these pools grows Monniera monniera {Her- 

 pestis monniera H. B. K.) in its aquatic, partially submerged form 

 with elongated stems, as well as Ammannia hoehnei, Phichea ccnn- 

 pliorata, and a species of Eleocharis. 



DUNE-MARSH FORMATION. 



A low, rather scanty vegetation covers limited areas of wet sand 

 which fringe the reed marsh, separating it from the dry strand, and 

 also occurs here and there in depressions among the dunes. The 

 most characteristic species are the terrestrial form of Monniera vion- 

 nier a ^yith short internodes, and Lippia nodiflora, both having repent 

 stems rooting at frequent intervals and leaves usually appressed to 

 the ground. In the case of Lippia, however, the leaves are sometimes 

 nearly vertical in strong sunlight, giving the plant a peculiar appear- 

 ance. Each of these species sometimes occupies small tracts to the 

 exclusion of other vegetation. They usually grow together, however, 

 and in association with Hydrocotyle umhellata, Centella asiatica, and 

 Diodia virginiana, all small plants with creeping or prostrate stems. 

 Among the dunes Lippia and Herpestis sometimes play a less impor- 

 tant part, and an assemblage of species, some of which are not nor- 

 mally halophilous, covers the ground. Of these Juncus dichoiomus, 

 J. scirpoides, Scirpus americanus {S. piingens), Trigloch in striata, and 

 Mikania scandens are more at home in saline soils, while Ludwigia 

 7nicrocarpa, L. alata, Cynoctouuni mitreola {Mitreola petiolata), and 

 Dicliromena colorata (D. leucocepliala) are character plants of the 

 fresh- water marshes of the region. Such commingling is perhaps to 

 be explained by the fact that these hollows among the dunes derive 

 their moisture largely from the rainfall, while, on the other hand, 

 siDray-laden winds contribute a certain amount of salt to the soil. 



TIDAL FLAT FORMATION. 



This is an open formation, occupying the margins of the shallow 

 lagoon at the lower end of the island, which is under water at flood 

 tide. The soil is a mixture of silt and sand. A sparse growth of 

 Sesurium maritimuni (S. pentandrum), Tissa marina {Lepigonum 

 salinum), and Scirpus americanus forms a characteristic association. 

 Faspalum disticlimn, with prostrate culms, sometimes 2 meters long, 

 rooting at the nodes, as well as scattered erect tufts of Fimbristylis 

 spadicea, were the only other species observed in this formation. 



