360 PLANT-LIFE 



Let us in brief outline consider a dune-formation. 

 High winds blowing upon a sandy shore blow the sand 

 inland, and it accumulates in the form of dunes or sand- 

 hills. These dunes frequently shift unless they are 

 covered with vegetation. A dune is to all intents and 

 purposes a desert, but yet it can be colonized by xero- 

 phytes, which are adapted to life in physically dry con- 

 ditions. A shifting dune may become " fixed " by the 

 vegetation which occupies it. While the dune is yet 

 liable to shifting under the influence of high winds, and 

 its seaward side is bare, the landward slopes become 

 occupied by various xerophytes, and the crest is tackled 

 by the Sea-Maram Grass (Psamma arenaria), which has 

 very long creeping rootstocks that penetrate deeply into 

 the sand in search of moisture, and very materially 

 assist in binding the sand and fixing it so that it is not 

 so readily dispersed by wind. The Maram Grass is 

 followed by other plants, all with long roots and devices 

 which check transpiration. Among the plants that 

 colonize the dune, particularly on its landward slopes, 

 are the Sand Sedge (Carex arenaria), the Sea-Holly 

 (Eryngium maritimum, Plate LXXIL), the Rest-Harrow 

 (Ononis arvensis), the Sow-Thistle (Sonchus oleraceus), 

 Sea-Buckthorn (Hiffophos rhamnoides), Henbane (Hyo- 

 scyamus niger, Plate XX.), and the Yellow-Horned 

 Poppy (Glaucium luteum, Plate LXXIIL). 



At a later stage the dune is more settled, but the 

 Maram Grass remains dominant and other species 

 already mentioned may persist. But in time many 

 new plants gain foothold and become abundant. Among 

 these are Wild Thyme (Thymus Serpyllum), Lady's 

 Bedstraw (Galium verwn), Stork's-Bill (Erodium cicu- 



