VEGETATION OF THE SEA-COAST 385 



leeward side, plants secure a better footing, and more 

 numerous species are found, which have usually long 

 rhizomes or deep-growing roots, e. g. Sea Purslane (Arenaria 

 peploides), Sea Holly (Eryngium maritimum), Ragwort 

 (Senecio Jacobaea), a variety of the Dandelion {Taraxacum 

 erythrospermum) , Hawkweed (Hieraceum umbellatum) , Cat's- 

 ear (Hypochaeris radicata), Sea Bindweed (Calystegia Solda- 

 nella), Sea Spurge (Euphorbia Par alias), Sea Buckthorn 

 (Hippophae rhamnoides), Sand-sedge (Car ex arenaria), 

 Fescue-grasses (Festuca rubra var. arenaria and Festuca uni- 

 glumis), Sea Couch-grass (Agropyron junceum), and Lichens. 

 The vegetation of the sand-dune differs in several impor- 

 tant respects from that of the salt-marsh. The soil-water of 

 sandy shores does not usually contain much salt, and the 

 plants growing there, though subjected to the influence of 

 salt spray from the sea, are not halophytes. The mobility of 

 the sand, unsuited to most perennials, is the main factor which 

 determines the character of the vegetation. Our previous 

 experiments on soils have shown that the capillarity of sand 

 is less than that of ordinary soil, that water percolates 

 quickly, and that the water-capacity of the sand is slight. 

 White sand reflects the heat of the sun, the surface layers 

 become rapidly heated, water is quickly driven off, and the 

 air around is hot and dry. At night rapid cooling occurs and 

 the surface conditions resemble those of a desert. Although 

 much organic matter may be strewn over the surface, rapid 

 oxidation takes place, and the sand in consequence is poor 

 in humus. Rapid percolation of water may also tend to 

 deplete it, and thus the sand is poor in food-materials. 

 Further, if a soil which dries rapidly contains 1 per cent, 

 of salt it may act as a poison to most plants, though they 

 may be able to withstand two or three times that amount 

 in a soil which does not rapidly dry. If the surface layer 

 of sand is removed, the lower layers are found to contain 

 much moisture even in dry seasons. This moisture is 



1296 b b 



