268 PSAMMOPHYTES SECT, x 



the dorsal side opposed to the wind ; this firm, smooth, and glossy dorsal 

 side is provided with hypodermal sclerenchyma. 



Efficient protection against the force of the wind is supplied by the 

 large leaf-sheaths that for a long time enclose the inflorescences of the 

 sea-marram, Elymus arenarius, and Weingaertneria and other grasses. 



Deep-growing, only slightly branched, roots, which not only prevent 

 the plant from being dislodged, but also raise water from the depths 

 when the surface is dry, are possessed by many species, including Psamma 

 arenaria, Elymus arenarius, Carex arenaria (with two kinds of roots), 1 

 and Eryngium. 



The root-hairs function for a long time ; grains of sand cling firmly 

 on to the roots of the sea-marram, lyme-grass, Koeleria glauca, and 

 others, and sometimes encase the roots in firm tubes. 



Dune- Heath. 



On many grey dunes and on old-established sand-fields there develop 

 various dwarf-shrubs, but particularly Empetrum nigrum and Calluna 

 vulgaris, also Genista anglica, Rosa pimpinellaefolia, and small specimens 

 of Salix repens. Among these Calluna vulgaris may attain an enormous 

 distribution, so that grey dune is changed into dune-heath callunetum 

 in which ordinary heath-plants are intermingled with dune-plants. In such 

 heath hard pan does not seem to occur, and raw humus is scarcely developed. 2 



Dune-Bushland. 



Many old dunes in northern Europe become occupied by taller shrubs, 

 so that bushy vegetation arises on them. Hippophae rhamnoides is 

 especially liable to appear in these circumstances. On certain dunes on 

 the eastern and southern coasts of the North Sea there are extensive, 

 thorny, dense, impenetrable thickets of Hippophae hippophaeta. The 

 xerophytic nature of this shrub is expressed in the narrow leaves and 

 their dense coating of scaly hairs, and in the thorns. In the shade of 

 these shrubs there flourishes a flora that somewhat partakes of the 

 character of the ground-flora of forest. 



Salicetum also occurs and is composed of Salix repens, together with 

 rose-bushes, Sarothamnus scoparius, and Populus tremula ; but it is 

 of limited distribution. 



Dune-Forest. 



In Denmark artificial forests occur on dunes, and include Pinus 

 montana, Picea alba, and, in older plantations, Pinus sylvestris, P. 

 austriaca, Picea excelsa, and others. But on the Baltic coasts natural 

 pine-forests thrive on dunes. 3 



Other Examples and Distribution of Psammophilous Vegetation. 



Psammophilous vegetation showing the same and different defences 

 against transpiration occurs in other parts of the Earth, and includes many 

 species, growth-forms, and formations which are unfamiliar to us and 



1 Buchenau, 1890; Warming, 1891. * See Chap. LII, pp. 2 1 2-3. 



* Concerning bushland and forest on dunes in northern Europe, see Warming, 

 1891, 1907-9; and Abromeit in Gerhardt, 1900. 



