THE FLORA 89 



that ihe crust of the island is formed of hard rock, imper- 

 meable to moisture. It is covered with a shallow layer of 

 soil, in many places not more than a few inches in depth. 

 The rain that falls, instead of percolating downwards as it 

 would do if the understratum were pervious, runs along 

 the surface of the rock, or lies in natural basins, forming 

 marshy ground. The water from such situations does not 

 drain away, but is mainly carried off by evaporation a slow 

 process, resulting in much loss of heat to the ground. 



Owing to the proportionately large extent of coast-line in 

 comparison with the inland area, seashore plants form, as 

 might be expected, an important element of the island 

 flora. The northern shore-line, with the exception of 

 Kiloran Bay and the vicinity, is almost wholly rocky, with 

 characteristic sea-rock plants. Salt-marshes, sandy and shingly 

 bays, alternate \vith rocky promontories round the southern 

 half of the island. Shore pools are frequent on the western 

 shore, and are inhabited by curious plants species of Toly- 

 pella, Euppia, Chara, Potamogeton, etc. with a decided 

 preference for brackish water. 



Characteristic Plants of the Shore 



Plants of the Sea- rocks. Ligusticum scoticum, Spergu- 

 laria rupestris, Crithmum maritimum (rare), Beta maritima 

 {rare). Asplenium marinum, Sedum roseurn, Silene maritima, 

 and Statice maritima, though abundant on the sea-rocks, are 

 occasionally found growing in other situations. 



Plants of the Sandy Shore. Salsola Kali, Atriplex 

 laciniata, Cakile maritima, Eryngium maritimum (rare). 



Plants of the Salt-marsh. Salicornia herbacea, Suceda 

 maritima, Triglochin maritimum, Juncus Gerardi, Scirpus 

 maritimus, Glyceria maritima, Carex vulpina, etc. 



The presence or absence of lime is one of the most 

 important particulars in which petrology affects the distribu- 



