MEDITERRANEAN REGION. 273 



quickly become filled with Protococcaceae. The algae are followed by saxi- 

 cole lichens, which produce more rapid weathering of the surface, as a result 

 of the action of rhizoids especially. Upon recent lava only a faint trace of 

 Protococcaceae and diatoms can be found, while lichens begin to appear in 

 about 7 years. Stereocaulon vesuvianum is the first pioneer, but it is soon 

 followed by a number of other Kchens. Organic materials increase, and 

 mosses appear, viz, Bryum, Phascum, Grimmia, etc., while liverworts, such as 

 Jungermannia, develop in the shady spots. A soil is formed steadily by the 

 action of the lichens and mosses, and its depth is increased by the fall of ashes, 

 pumice, etc. Gymnogramme leptophylla and Adiantum capiUiis-^eneris appear 

 in the moist shady clefts, while the characteristic Cheilanthes odora, together 

 with Ceterach offidnarum, Polypodium vulgare, Asplenium trichomanes, and 

 Adiantum nigrum, occurs in more xerophytic situations. 



Meanwhile, flowering plants have begun to appear in more exposed places. 

 The first invader is Centranthus ruber, followed by Sedum rufescens, Heli- 

 chrysum litoreum, and Rumex bucephalophorus, Picridium, Reseda, etc. All 

 of these are xerophytes, and many are succulent. The grass stage is repre- 

 sented at first by small forms, such as Poa bulbosa, Aira cupaniana, Cory- 

 nephorus articulatus, Psilurus nardoides, Lagurus ovaius, Festuca ciliata, and 

 F. bromoides, after which appear Hordeum leporinum, Poa annua, and Phleum 

 michelii, and finally Agropyrum repens, Andropogon hirius, and Imperata 

 arundinacea. In about 20 years the soil upon the lava has become deep 

 enough for woody plants, of which Spartium junceum is the first. This is 

 followed by Spartium scoparium and Artemisia variabilis. These yield to 

 shrubs and trees, which finally constitute a true woodland. 



FlahauU and Combres (1894) have studied the vegetation of the Camargue 

 and the alluvial area at the mouth of the Rh6ne: 



The most important formations of the Camargue are (1) sansouires, (2) flat 

 sandstrand, (3) dunes. The sansouires are moist alluvial soils clothed with 

 Salicornia spp. and Atriplex portulacoides, which constitute the chief forage 

 for grazing animals. Sansouires are subdivided into salty wet areas domi- 

 nated by Salicornia sarmentosa, Statice, etc., and dry areas with Salicornia 

 fruticosa, Juncus nmritimus, J. gerardi, etc. The flat sandy areas, when pro- 

 tected from fire, are colonized by Salicornia macrostachya, with which other 

 halophytes associate themselves and build small island-like elevations, or 

 touradons, which are mostly 2 meters wide and but 3 or 4 inches high. Upon 

 these are found chiefly Salicornia fruticosa. Inula crithmoides, Juncus mari- 

 timus, etc. The dunes are poorly developed. They are regularly formed, 

 however, in protected places and are quickly covered and fixed by a vegetation 

 partly with horizontal rootstocks, Juncus muriiimus, Cynodon dactylon, 

 Scirpus, Eryngium, Agropyrum, etc., or with deep rhizomes, Ammophila, 

 Echinophora, etc. Behind the recent dunes are found older ones which bear 

 a richer, less halophilous vegetation. Upon the highest of these are found 

 woods of pine with various shrubs. Between the dunes are old brackish 

 sansouires, while another old dime region is now clothed with typical maquis. 



Adamovic (1899) has found that the swamps of the lakes and streams of 

 eastern Serbia are initiated by Phragmites, the rootstocks of which are carried 

 by the water into shallow areas, where they take root and quickly form a stand : 



This permits the establishment of a number of aquatics, Alisma, Butomus, 

 Hippuris, Polygonum amphibium, etc., which are soon suppressed by the true 

 swamp-plants. The most important of these are Sdrpv^ lacustris, trigueter, 

 maritimus, and silvaticus, and Juncus glaucus, compressus, and lamprocarpus. 



