12 THE VEGETATIOIV OF SHACKLEFORD BANK 



c. Isnardia-Pluchea association. 



d. Acorus-Salix association. 



4. Tidal flat formation (closed): 8cirpns-Pas}}aJum association. 



I. Sand strand vegetation. 



1. Treeless (open). 



a. Inner beach formation. 

 This formation fringes the sound side of Shackleford except in a few 

 places where the salt marsh extends to the water's edge. The soil is a 

 fine sand, bare of vegetation up to the limits of mean high tide. Above 

 this limit Spartina patens, Cenclirus trihuloides, and Croton maritimus. 

 all perennial species, occur commonly, though not covering the ground 

 completely", Chenopodmm Botrys, Phy salts viscosa, and Salsola Kali 

 are of common, though not universal, occurrence. 



h. Outer beach formation. 



The sandy soil is mixed with broken fragments of shells. The soil 

 water stands at a depth of about 12 inches, and is fresh. The outer 

 beach is overrun by the highest Avinter tides, but is above the mean high- 

 tide line. 



The vegetation is sparse and open, the individual plants standing at 

 wide intervals. The loose character of the soil imparts a desert aspect 

 to the vegetation. Salsola Kali, Euphorbia polygonifoUa, and Ama- 

 ranthus pumilus are characteristic of this formation. Fimbristylis cas- 

 tanea and Spartina juncea (patens) occur occasionally. 



c. Dune formation. 



The sand accumulated on the dunes is Avind-blown and of fine texture. 

 The soil water is fresh and stands at a depth of 18-24 inches. 



The dunes are covered with Uniola paniculata, whose flowering stalks, 

 sent up in abundance, are very striking. This species appears to set 

 seed rarely in this locality. Besides the Uniola, Physalis viscosa, Cro- 

 ton punctatus, Solidago sempervirens, and Oenothera humifusa are pres- 

 ent. This formation reaches its best development on the neighboring 

 Bogue Bank. (See Plates II A and B and Plate III yl.) 



2. Trees and shrubs. 



a. Thicket formation. 



The soil is sandy, with a slight admixture of humus. Owing to its 

 being completely shaded, it dries out much less readily than the open 

 sandy soil of the preceding formations. 



Ilex vomitoria, from a few inches to 3 feet high, covers the ground 

 so closely that one can with difficulty make his way through the thickets. 

 Where a break occurs in the vegetation, Ilex opaca, Juniperus virgin- 

 iana, Smilax Bona-nox, Myrica carolinensis, and other species occur. 



