224 HALOPHYTES SECT, vn 



CHAPTER LVI. LITHOPHILOUS HALOPHYTES 



ON rocks near the sea plants acquire xerophytic structure for two 

 reasons : first, the general one that the substratum is rock, 1 and, 

 secondly, proximity to the sea. Spray cast up by the breakers, and 

 particles of salt deposited by foam and wind on the plants, introduce 

 a floristic modification into the rock- vegetation, so that there is an ad- 

 mixture of halophytes or it is purely halophytic. There thus come into 

 being communities, including those composed of lichens, which display a 

 zonal distribution. On granite rocks at Bornholm (in Denmark), at Kullen 

 (in Sweden), and elsewhere on northern coasts, the vegetation is arranged 

 in several belts. Lying lowest, where the rocks are very frequently 

 wet, is Verrucaria maura, a very thin black scaly lichen divided into 

 small pieces ; this lichen is widespread along the coasts of northern and 

 arctic seas. Higher up, the rocks are reddish yellow with Placodium 

 murale, which is accompanied by Xanthoria parietina. Above this 

 follows a belt of Ramalina scopulorum ; here the action of the salt- 

 water is reduced to little or almost nothing. In the first two lichen- 

 belts cracks in the rock entertain halophytic Spermophyta, including 

 Matricaria maritima, Aster Tripolium, and species of Atriplex. A little 

 higher the action of the salt water vanishes, and the vegetation on littoral 

 rocks is identical with that on inland rocks. 2 



Similar vegetation colonizes rocks on Adriatic shores. Here, like- 

 wise, Verrucaria maura clothes wet rocks with its ' often pitch-black 

 crusts ', and in the clefts of the cliffs are lodged fleshy-leaved halophytes, 

 including Crithmum maritimum, Statice cancellata, Inula crithmoides, 

 and others. 3 



In Madeira on rocks exposed to salt water are a few succulent plants. 

 Dotted here and there is an individual of Mesembryanthemum nodi- 

 florum, Portulaca oleracea, Beta maritima, or Crithmum maritimum. 4 

 On the Canary Isles, inaccessible rocks, which are constantly wet with 

 salt sea-spray from the breakers, are gay with numerous species of 

 Statice, which possess large light-green rosettes of leaves, and blue, red, 

 or white blossom, surmounting inflorescences that are about half a metre 

 in height. 5 Rocks on the shore often entertain extremely halophytic 

 spermophytic species that do not grow in any other habitats ; such is 

 the case on the Mediterranean, in the West Indies, and other places. 



In this, as in other cases of rock-vegetation, a distinction must be 

 drawn between those species that are truly attached to the rock, and 

 those (chasmophytes) that are rooted in earth contained in crevices : 

 this distinction was noted by Schimper. 6 The former plants possibly 

 include only lichens, algae, and perhaps some mosses. 



Lithophilous vegetation on sea-shores has been the subject of but 

 little investigation. 



Compare Chapter XLI on Lithophilous Benthos of the sea-shore, into 

 which this may pass. 



1 See p. 238. ' Warming, 1906. 3 Beck von Mannagetta, 1901. 4 Vahl, 19046. 

 1 Christ, 1885; C. Schroter, 1908. * Schimper, 1898; Cockayne, 1901 ; Ottli, 1903. 



