386 ECOLOGY 



probably derived from internal dew in the sand. The 

 plants able to withstand salting and to endure the severe 

 conditions along the shore are few in number and for the 

 most part xerophytes,with tough, leathery, rolled or reduced 

 leaves (Fig. 248). In some the leaves are fleshy and often 

 coated with wax, others are spiny, and plants with branch 

 spines are not uncommon. Grey-green is the prevailing 

 colour of the vegetation. 



The names ' shifting dunes ', ' travelling dunes ', ' grey 

 dunes ', and ' white dunes ', by which sand-hills are com- 

 monly known, are suggestive of their most characteristic 

 features. Beyond the shifting dunes, and farther from 

 the influence of mobile sand, a grassy vegetation develops, 

 which forms a sod, covering and protecting the sand. The 

 dunes are low, the sand is more firmly fixed, and contains 

 more humus ; there is greater variety of soil and surface, and 

 in consequence a much more varied flora is supported. 

 On the one hand are the dry sand-banks with their grey- 

 green xerophytes, and on the other, wet hollows supporting 

 a marsh vegetation. To this part of the coast the name 

 ' fixed dune ' is given ; nevertheless, the area is liable to be 

 covered during high winds by blown sand, and this has an 

 influence on the character of the vegetation. Cultivated 

 crops farther inland often suffer materially from the effects 

 of blown sand. The dominant plants of the fixed dune are : 

 Sand-sedge {Car ex arenaria), Fescue-grass (Festuca rubra 

 var. arenaria), and sometimes Sea Couch-grass (Agropyron 

 junceum). Associated with these and sometimes abundant 

 are Sea Cat's-tail-grass (Phleum arenarium), Rest-harrow 

 (Ononis repens), Stork's-bill (Er odium cicutarium), Bird's- 

 foot Trefoil (Lotus comiculatus) , together with species 

 occurring on the shifting dunes, and numerous species 

 which have migrated from adjacent pastures and meadows. 

 In places, bushes are so abundant as to form thickets, e. g. 

 Dwarf Willow (Salix repens), Sea Buckthorn (Hippophae 



