CHAP. LV ADAPTATIONS OF HALOPHYTES 223 



But more probable is another explanation offered by Schimper, 

 namely, that the protective arrangements against intense transpiration 

 are required owing to the plant finding it difficult to absorb water 

 from a relatively concentrated salt solution ; this latter truth was first 

 demonstrated by Sachs in 1859 J ; a saline soil is therefore physiologi- 

 cally dry. 



The statement made by Stahl 2 that halophytes are incapable of 

 closing their stomata and of thus regulating their transpiration, does 

 not correspond with fact, according to Rosenberg, 3 Benecke, 4 and 

 Diels. 5 



Halophytic communities may be divided into those that are lithophi- 

 lous, psammophilous, pelophilous, and helophilous, according as the 

 substratum consists respectively of rock and stones, of sand, of mud, 

 of swamp. There are communities consisting solely of thallophytes or 

 solely of herbs, and others including shrubs, trees, and true forest. 

 Lichens and mosses are very rare, yet some markedly halophilous species 

 occur. 



We shall deal with these plant-communities growing on saline soil 

 in five chapters, but this is only a matter of practical convenience. We 

 cannot speak of formations, because each chapter includes communities 

 differing so widely that they should properly be regarded as separate 

 formations, the growth-forms composing them being so diverse. The 

 following is the arrangement adopted : 



Lithophilous halophytes. 

 Psammophilous halophytes : 



(a) Sand-Algae, 



(b) Iron-sulphur-bacteria, 



(c) Halophilous herbs, 



(d) Shingle-banks, 



(e) Halophilous forest and bushland. 

 Pelophilous halophytes : 



(a) Aestuaria -with Zosteretum and Salicornietum, 



(b) Salt-meadow, 



(c) Salt-bushland, 



(d) Salt-steppe. 



Salt-swamp, and Salt-desert. 

 Littoral swamp-forest (mangrove). 



1 Also see Hedgecock, 1902. * Stahl, 1894. 



3 Rosenberg, 1897. 4 Benecke, 1901. 



8 Diels, 1898. There is an extensive literature dealing with the structure 

 and nature of halophytes : special reference may be made to the papers by Are- 

 schoug, Benecke, Brick, Contejean, Diels, Ganong, B. Jonsson, G. Karsten, Kearney, 

 Lesage, Ricome, Rosenberg, Schimper, J. Schmidt, Stahl, Volkens, and Warming. 



