234 HALOPHYTES sect, vii 



sions which contain salt water during the rainy season, but many of 

 which are dry and covered with incrustations of salt in summer. In them 

 grow Chenopodiaceae, Plumbaginaceae (Statice, Limoniastrum), Nitraria 

 dentata, Reaumuria vermiculata, Frankenia Reuteri, and others.^ 



Similar depressions occur scattered about countries that have a 

 marked continental, dry climate, for instance in the steppes of Hungary, 

 in southern Russia,^ in the interiors of Asia and North America,^ in 

 Austraha. The salt deserts of Argentina are often like vast snow-fields, 

 or ice-fields, but, in the rainy season, like lakes ; some of them are entirely 

 devoid of plants.* Among the Chenopodiaceae present are species of 

 Atriplex, Spirostachys, Halopephs, Suaeda ; among grasses, Munroa, 

 Muehlenbergia, Pappophorum, and Chloris. In addition there occur 

 Papilionaceae, Portulacaceae, Apocynaceae, Cactaceae, and others. 



Apparently almost wanting in plant-life, according to Buhse's descrip- 

 tion, is the great Persian salt-desert,^ which is more sterile than the Sahara 

 and covers one-thirtieth of Persia. The clay soil, which in deeper layers 

 assumes the form of mud, retains salt, and thus crystallizes out in places 

 so as to form incrustations as much as a foot in thickness. Of this 

 yellowish-grey tract, extending for 115 geographical miles, the main part 

 is sand, with which lime, oxide of iron, common salt, sodic sulphate, 

 and clay are mixed ; on it grows not a single plant, not a grass haulm, 

 not a moss, and not even any humbler plant : it is the desert of aU deserts. 



Of the oecology of salt-swamp but little is known. The growth- 

 forms present seem to be for the most part perennial herbs and shrubs. 

 Much more is known regarding the formation about to be described. 



CHAPTER LX. LITTORAL SWAMP-FOREST. MANGROVE 



Among all plant-communities confined to swamps in salt or brackish 

 water mangrove-swamp is the most extensive and interesting, as well as 

 the best known. It occurs by all tropical seas, especially on flat, muddy 

 shores, where the water is relatively calm, as in lagoons, inlets, estuaries, 

 but not where rocky soil and breakers prevail ; the soil is flooded with |i 

 water either permanently or at high tide. In many places mangrove- 

 vegetation extends far inland along the banks of large rivers. The 

 water is usually more or less brackish, as far as the tide extends. 



Mangrove-vegetation mostly assumes the form of low forest or bush- 

 land, and, viewed from the sea, reveals itself as a dark-green, dense, 

 often impenetrable mass of low trees with countless arched aerial roots. 

 Rhizophora Mangle in favourable sites in the West, for instance at the 

 mouths of rivers in Venezuela, like R. mucronata in the East, grows 

 up to produce stately high-forest.'^ The bottoms of the crowns of the trees 

 are usually truncate, and stand a small distance above the water, and 

 beneath them one sees, where Rhizophora-vegetation forms the outermost 



' Massart, 1898. 



^ See Krasnoff, 1886 ; Tanfiljew, 1905 ; Basiner, 1848. 

 ^ See Hitchcock, 1898. ' Brackebusch, 1893. 



* Buhse, 1850. 



* ' Tidal forest ' of various writers, including Tansley and Fritsch (1905). j 

 ' Johow, 18846. 



