280 



BKITISH 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 CaJcile 

 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. 



FIG. 114. Carex arenaria, WITH RHIZOME NEAR SURFACE OF SAND. 



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 



