134 PLANT-LIFE ON LAND [CH. 



growing upwards to the light when it may have been 

 completely covered by blown sand. The more rapidly 

 and effectively this can be accomplished the greater 

 will be growth of the Dune. Lastly, owing to the 

 low specific heat of the sand, and its free exposure, 

 and the consequent rapid cooling at night and liability 

 to sudden heat during the day, it will be necessary 

 that the plants of the Dune-flora shall be xerophyti- 

 cally adapted, that is, that they shall be able to stand 

 sudden conditions of extreme heat and drought. It 

 will be apparent that relatively few plants are in a 

 position to meet all these requirements, and it need 

 therefore be no matter for surprise that the Dune- 

 forming Flora is a restricted one. 



By far the most common and efifective Dune- 

 forming plant is the Marram Grass, or " Bent " as it 

 is called by golfers {Ammo})Mla arundinacea). It 

 will therefore be worth while to examine the Bent 

 Grass carefully. It appears coarsely and densely 

 tufted above ground, with long leaves sheathing 

 below, but narrow in form, and very gracefully curved 

 in their upper region. They are furnished with 

 sharply pricking points, and doubtless these aid the 

 young growing leaves in making their way upward 

 through the sand. Examining the leaf it is seen to 

 have a convex surface (the lower or abaxial), which 

 is hard and smooth, and a concave surface (the upper 

 or adaxial), which is marked by deep longitudinal 



