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783 The Vegetation of the Sea-coast. 
2 
8. Rock and Cliff. 
6, ı a. General. 
Rock-surfaces are common on the coast and vary from high vertical clifts, : 
their bases washed by the waves, to flat sea-worn rocks hardly raised above 
the water. According to the nature and aspect of the rock most diverse stations 
are available for plant-life. On a vertical wall of hard rock with an even 
surface exposed to a maximum of salt-spray, there are no plants except a 
few lichens, but a sheltered rock in a rainy locality with many cracks, crevices 
and ledges, where soil can lodge, will support a rich vegetation. 
Although rock-associations are at first open, rooting-places are so limite 
in area, that there may be keen competition between the early comers. 
‚ soil-making ability of the plants may have much influence upon the ultimate 
composition of the association, certain peat-formers being able to furnish a soil 
of considerable depth and great water-holding capacity. Chasmophytes canno 
gain a footing, until there be sufficient soil in the cracks or crevices. This 
_ may consist of small rock-fragments and sand weathered zn szzu, or blown soil. 
Accumulations, 2.5—5 cm in depth, are quite frequent. The seedlings must 
be able to tolerate periods of drought. Succulency, thick coriaceous leaves, 
prostrate and rosette-forms are frequent and advantageous. Often the roots form 
a mat, as with certain ek lens, while even sep: roots may at first exten 
ee Iaterally along. a fissure. 
® re not easy to. draw che ine : as to true coastal-rock formations. Thus, 
