SAND DUNES 129 



guard in the form of plants belonging to various 

 affinities, but having this in common that they are 

 of low stature, and of more or less creeping habit. 

 They are characteristically " Halophytes," that is 

 denizens of saline soil, and most of them bear the 

 mark of it in their fleshy habit, their smooth hairless 

 surfaces, and their bluish tint due to a thin protective 

 covering of wax. Among such may be seen at the 

 lowest levels the Orache (Atriplex\ and Seablite 

 (Suaeda), the Sea-Rocket (Cakile), the Salt- Wort 

 (Salsola) (Fig. 21), and Sea Purslane (Arenaria pep- 

 loides) : with these, or often forming dense patches by 

 themselves, are found the Sea-Couch Grass (Triticum 

 junceum), and the Common Sand Sedge (Carex 

 arenaria). These plants are joined not uncommonly 

 by some ordinary land-plants, such as the Silver Weed 

 (Potentilla anserina), and various forms of the Couch 

 Grass (Triticum repens). An interesting though rare 

 plant that shares this habitat is the pink-flowering 

 Convolvulus (O. soldanelld) : it creeps along the sand 

 much in the same way as its relative, Ipomaea pes- 

 caprae, which is a notable sand-binder of tropical 

 shores. Such plants as these, or various representa- 

 tives and combinations of them, by their mode of 

 growth give a coherence to the otherwise loose sand, 

 binding it together by their roots and runners. At the 

 same time, when wind is drifting the loose grains 

 along the shore, the shoots and foliage of the growing 



