THE ECOLOGY OF PLANTS. 437 



bind the shifting sand together. The rhizome of Sand 

 Sedge {Car ex arenaria, habit like that of the Sedge shown 

 in Fig. 60) burrows deeply and runs in straight lines, sending 

 up aerial shoots, which are therefore arranged in lines along 

 the surface of the sand. The chief Grasses which bind the 

 sand and can withstand being buried by it occasionally are 

 the Marram-grass (Psamma arenaria} and the Lyme-grass 

 (Elymus). Other sand-binding grasses are Sea Couch- 

 grass (Agropyron junceum), and the rather local maritime 

 species of Phleum, Poa, Bromus, Festuca, etc. ; Sea Barley is 

 very common on our coasts, but it has no creeping rhizome, 

 and is an annual plant. 



The dune hollows, where not liable to inundation at high 

 tides, often collect rain water and become pools, covered at 

 first by slimy green algae, which make the substratum imper- 

 vious enough to retain water through winter and spring at 

 any rate, and prepare the way for mosses and liverworts, 

 which in turn produce a fairly retentive bottom. If these 

 hollows collect enough water, Sedges, Rushes, and various 

 other freshwater marsh plants appear Creeping Willow, 

 Cross-leaved Heath, Marsh Stitchwort, Water Purslane, Bog 

 Pimpernal, Stinking Iris, etc. If the pools are too wefi 

 drained, various G-rasses (Agrostis, Nardus, Festuca, etc.) 

 may become dominant, along with such plants as Stork's- 

 bill, White Clover, Stonecrop, Silverweed, Ragwort, Ling, 

 Bell Heath, etc. 



Further back from the sea the dunes become more fixed and also 

 levelled by wind, rain, and rabbits, producing in many places fine golf- 

 ing turf. Here we get a vegetation of the dry-pasture type, including 

 various Grasses (Cock's-foot, Rye-grass, Yorkshire Fog, Fescues, etc. ), 

 with Field Woodrush, Bird's-foot Trefoil, Bird's-foot, Gorse, Brambles, 

 Petty Whin, Medicks, Clovers, Burnet Rose, Silverweed, Red Centaury 

 (Erythraea, a Gentian with pink flowers in cymes), Thyme, Ling, Milk- 

 wort, Heath Bedstraw, Stork's-bill, Sorrel Dock, Milfoil, Ragwort, 

 Cat's-ear, Autumn Hawkbit, Scentless Mayweed, Speedwells, Stone- 

 crop, Dog Violet, Hound's-tongue, Viper's Bugloss, and many herb- 

 aceous and low-growing plants. 



414. On shingle and pebble beaches there is usually 

 a rather limited vegetation, and most of the plants have long 

 roots which can reach the moist soil below the pebbles. Near 

 the sea we usually find various Oraches, Sea Beet, Saltwort, 



