28 THE GEOGRAPHY OF PLANTS. 



sand-reed, or marrams, (Ammophila arenariaj) 

 the sand-sedge, (Carex arenaria,) and the sea 

 lime-grass, (Elymus arenarius,) have been es- 

 pecially useful in restraining the encroachments 

 of the sea on sandy shores. This they do by 

 their long, creeping shoots and tough, tangled 

 roots, which, running among the sands in every 

 direction, so bind them together, that they offer 

 a resistance rarely overcome by the force of 

 storms, and are renewed as fast as they are 

 destroyed. When these natural defences have 

 been uprooted by the thoughtlessness or igno- 

 rance of man, the most serious evils have arisen. 

 In Scotland, for example, large tracts of once 

 fertile country Jiave been rendered barren by 

 the encroachment of sand-hills, which have 

 given them the desert-like aspect of Egyptian 

 plains ; and this encroachment has resulted 

 from the destruction of the mat-grasses, which 

 were pulled up by the country people for fuel 

 to such an extent, that an act of parliament was 

 passed, about one hundred years ago, rendering 

 it punishable to do so. 



Chalk plants grow on calcareous soils. Among 

 these may be enumerated many of our prettiest 

 wild plants in England, as the yellow wort, 

 (Chlora perfoliata^) the squinancy wort, or small 

 woodruff, (Asperula cynanclrica,) and most of 

 our native species of the orchis tribe, which 

 adorn many a chalky spot with their beautiful 

 flowers. One considerable genus of plants 

 (Gypsophild) is only found on rocks composed 

 of gypsum, or sulphate of lime. 



