142 PLANT-LIFE ON LAND [CH. vm 



little Burnet Rose (Rosa spinosissima) or the Rest 

 Harrow (Ononis spinosa) may add a charm as well 

 as a permanence to the formation. Of the larger 

 woody growths which often follow the formation of 

 permanent Dune, one of the most effective plants is 

 the Sea Buckthorn (Hippophae rhamnoides\ which 

 is native in the south and is naturalised in Scotland. 

 Not only is it xerophytic in its character, but it also 

 fulfils the condition of spreading by the formation 

 of adventitious buds on its long creeping roots. 

 Lastly, such xerophytes as Gorse and the Heaths 

 and Ling, make their appearance as well, and when 

 once the Grey Dune is thus permanently established 

 many other plants follow, and constitute a Flora of 

 ever-increasing variety. 



And so what is at first an unstable formation 

 becomes compacted till it acquires a settled character. 

 It must not, however, be thought that actual encroach- 

 ment upon the sea itself is a common occurrence. 

 Doubtless plant-growths, upon which Dune-formation 

 depends, are continually edging seawards ; but they 

 are liable to be as continually checked and curtailed 

 by the action of the waves at high water in stormy 

 weather. The methods of Dune-formation are not 

 aggressive : they are rather those of defence, prevent- 

 ing inroads. Consequently Dunes are most commonly 

 found to run in concave curves between headlands, 

 and to round off the indentations of the coast-line, 



