280 BRITISH PLANTS 
the plants is heavily laden with salt, and they are therefore 
halophytes. The most frequent plants are low-growing 
annuals, which have no power of growing upwards when 
covered with sand, and this zone is consequently absent 
where the sand is advancing on the sea. Perennials are 
very rare, and occur sporadically, for the plants may be 
uprooted during storms, and only those which produce a 
large quantity of seed each year, as in annuals, can persist. 
The most common member of this association is Cakile 
maritima (sea-rocket), a fleshy-leaved plant belonging to 
the Wallflower-family. Several plants belonging to the 
Chenopod-family usually occur—e.g., Salsola Kali (salt- 
wort), with short prickly leaves, Atriplex patula, A. 
WAV AT? | 
Fic. 114.—Carex arenaria, witH RHIZOME NEAR SURFACE OF SanpD. 
hastata, A. Babingtonii (oraches), Chenopodium rubrum, and 
C. album (goosefoots). Arenaria peploides (sea-purslane) 
is the only perennial which is found at all constantly in 
this zone, and then only very sparingly. 
Above the strand-vegetation the sand is usually loose. 
The first plant to colonize this drifting sand is Agropyron 
junceum (sea couch-grass), which possesses long under- 
ground rhizomes bearing tufts of leaves at intervals. The 
sand is held at the base of the leaves, and as it increases 
in amount so the leaves grow upwards, and retain yet 
more sand. In this way a low embryonic dune is built 
up. Carex arenaria (Fig. 114), a plant of similar habit to 
the sea couch-grass, is sometimes associated with that 
grass in forming these dunes. When the sand has been 
