308 BOTANICAL SURVEY OF DISMAL SWAMP REGION. 



and low outer dunes, bearing a particularly sparse, almost entirely 

 herbaceous, growth, composed of very few speeies; (2) the higher 



middle dunes (white dunes or sen dunes), with their summits often 

 crowned with small thickets, and with a more abundant and diversi- 

 fied herbaceous vegetation, especially in the depressions among them; 

 and (;5) the innermost, highest dunes (gray or land dimes), which are 

 almost always covered with pine forest.' In the third belt may best 

 be included the flat, dry pine woods that almost always occur imme- 

 diately behind the dunes. 



BEACH AND OUTER DUNES. 



The outermost line of dunes is usually only 2 meters or so above 

 high tide, and the sloping beach between it. and the water is com- 

 monly devoid of plant growth, although often strewn with sea 

 wrack (Zostcra marina) which lias been cast up by the waves. Some- 

 times, however, a few plants of sea rocket (Cakile edeiihtla) and 

 of saltwort (Salsola kali) are found here. Rarely Amvwdenia 

 (Honkenya) peploides occurs. The beach is the area character- 

 istically occupied in the Tropics by the Pes-caprae formation, which 

 is composed of such plants as Ipomoea pes-caprae and Spinifex 

 sqaarrasns. 2 



The outer line of dunes, usually less than breast-high and constantly 

 shifting, is inhabited by certain hardy, strong-rooting plants, which 

 send up numerous stems from their branching root stocks. Marram 

 grass (Ammophila arenaria), growing usually to a height of about*) 

 decimeters (2 feet), is the most abundant of these (fig. 5!)), but not 

 rarely gives place to small colonies of the handsome sea oats {Uniola 

 paniculata) (commonly 6 to 9 decimeters, 2 to 3 feet, high), which 

 entirely replaces Ammophila not far south of this region (fig. 60). 

 An aromatic composite, Iva imbricata, forms roundish clumps of 

 stout, nearly erect stems (usually about 6 decimeters, 2 feet, high), 

 and is the only noteworthy bright green plant of the outermost dunes 

 (fig. 61). 



Another grass similar in habit, to Uniola paniculata is Panicum 

 amarum minus, which is not uncommon on the outermost dunes. Its 

 strong, widely branching rhizomes send up numerous leafy branches, 

 but few that bear flowers. Tn this respect, also, it resembles Uniola 

 and Ammophila. Each of these three grasses seems generally to 

 grow only where the others are absent. It is not uncommon to see 

 one small dune held by Ammophila alone and its nearest neighbor 

 bearing only Uniola or Panicum. 



1 At Cape Henry the very high innermost dunes are not forested, and are almost 

 entirely bare of vegetation, the only growth being a few plants of Ammophila 

 arenaria. 



s See Schimper, lndomalayische Strandflora, pp. 77 to #4. See also p. ;itfo below. 



