THE COAST-FLORA OF THE CLACTON DISTRICT. 205 
(2.) The vegetation of the grey dune, the “ conquered land.” 
where the sand is fixed by a continuous carpet of plants. 
The representative plant of the white dune is Psamma aren- 
aria (Sea Marram). It grows in scattered tufts, each of which 
gives rise to a small sand-hill, which is held together by a 
very extensive system of rhizomes. Thus it becomes itself 
one of the chief agents in forming the elevated dunes. Of course 
Clacton does not offer any high or extensive dune, but just 
enough to study the main characteristics of its vegetation. 
The chief dangers to which plants on such sites are exposed 
are : (i) drought, (2) being laid bare, dechausse the French call 
it, (3) being buried, (4) being injured by the flying grains of 
sand or by the wind directly. It is a very striking lesson to 
notice with what diversity of means different plants meet the 
same difficulties. Here we find Eryngium maritimum (Sea 
Holly), unfortunately disappearing in those parts which are 
within reach of the more idle of the sea-side visitors ; its immense 
stock in the sand, its stiff, coriacious, bluish leaves need no 
■explanation. Convolvolns soldanella with its beautiful red 
flower, slightly winding stem, glossy leaves, and Arenaria pep - 
loides (another Sea-Purslane), a low succulent annual, I need 
only mention. Perhaps the most interesting of all anatomical 
peculiarities is the rolling-mechanism of the grass-leaves, notably 
in Psamma, but also in the other dune grasses, and in Spartina 
stricta (Bristle-grass). 
However, the vegetation soon conquers the feeble dune, 
and the so-called grey-dune vegetation arises. Marram grass 
and Sea Holly disappear, choked apparently by too many 
competitors. The chief characteristics of this association are 
lowness of growth and continuity. Planiago coronopus, Leon- 
todon aatumnale, Hypoclioeris radicata form rosettes, Armeria 
vulgaris (Thrift) becomes sometimes even a cushion-plant ; 
its root is richly ramified and bears a rosette of narrow leaves on 
every branch, the whole forming a hemispherical cushion ; the 
stem of Silene martima (Sea Campion) is decumbent ; mosses 
and lichens, of course, fit in with the general character. The 
obvious cause of the clinging to the ground is the necessity of 
holding the sand together. Incidentally this growth-form pro¬ 
tects them from the full force of the wind and keeps the moisture 
back in the soil. Rosettes are said to be caused by rapid altera- 
