SAND DUNES. 625 



for fixinf^ the sand comes the lyme-grass, and these two species 

 'are chiefly used for the purpose in Holland. 



Other plants grow in gradually among them ; at first lichens 

 and algae, then grasses, as for instance Arenaria iJeploides, L., 

 Aira canescens, L., couch-grass {Agropyrum repens, Beauv.), 

 and other plants, such as the sea-poppy, Glaucium luteiun, 

 Scop.; Lathijrus maritimus, Bigel; and Hieracium nmhellatum, 

 L., etc. Vasselot de Eegne gives a very complete botanical 

 list of dune plants. 



Several shrubs then appear on the land side of the dune, as 

 Salix repens, L. ; sea-buckthorn {Hippirphae rhnmnoides, L.) ; 

 Li/riion hdrJxinini, L. ; Tamarix, etc. 



4. MaiiiteiKincc of the Littoral Dune. 



When once the littoral dune has been raised to a proper 

 height and profile and fixed by means of sea marram, it is 

 necessary to maintain it constantly in the same state ; any 

 undue accumulation of sand in any part of the sea side of the 

 dune at once causes an inland draught of sand on both sides of 

 it, which if not at once attended to will breach the dune. 



Men termed gardes cantonniers are therefore stationed along 

 the littoral dune in Gascony, who cut away all vegetation except 

 the marram from its surface facing the sea, in order to prevent 

 undue accumulation of sand. As the marram grows readily 

 from cuttings during the colder six months in the year, the 

 workmen who cut it away from ridges plant it in depressions, 

 or if the season be too hot or dry for the cuttings to take root, 

 the pieces cut from ridges are merely placed on depressions. 

 In this way, by cutting away the marram where it is too dense, 

 and planting or j^lacing it in depressions, the proper contour 

 of the dune is maintained, as the sand accumulates behind the 

 marram, and is blown away wherever the latter is cut. 



In cases where the dune has been neglected and large 

 depressions have been formed, it may be necessary to use 

 wattle fencing to cause an accumulation of sand, but if ordinary 

 care be taken, the marram grass will suffice to keep the littoral 

 dune in good condition, and Grandjean believes that new 

 littoral dunes may be formed by means of it, without using the 

 fences described in section 3. 



F.P. S S 



