240 SUCCESSION IN EURASIA. 



tation or humidity. To be sure both are considerably greater along the coast 

 than in the interior, and the growth of the Sphagna should therefore increase 

 in the same direction. In reality, the reverse is true. 



"The most usual course of changes which the vegetation of the Sphagnum 

 hummocks imdergoes as a consequence of drying out, and which can be con- 

 firmed in the interior of the peninsula after a comparison with intermediate 

 stages, is the following in its larger aspects: The formerly abundant reed and 

 cotton grasses disappear more or less completely, while the dwarf shrubs 

 (Betula, MyrtiUus) spring up, and new moss forms, above aU, Polytrichum, 

 Gymnocybe, then Dicranum, Hypnum, and others crowd in between the older 

 ones. At the same time, the fruticose lichens appear also, at first Cladinae, 

 Sphaerophorus, and several Cladoniae, later also Cetrariae and Platysmata 

 as well as Alectoriae. In a later stage, not only the Cladinae, but also the 

 under-shrubs, among which Empetrum now occurs abundantly, begin to 

 become sickly, and simultaneously gray-white patches of Lecanora tartarea are 

 seen. The living Sphagnum moss disappeared earlier, and the other mosses 

 are gradually covered by the hchen crust. Single stems of Polytrichum and 

 small turfs of Dicranum are seen the longest. Of the fruticose lichens, the 

 Cladinae disappear first, while most of the Cladoniae are reduced to miserable 

 bits of thaUus and sterile podetia. At last the Alectoriae disappear and the 

 top of the hiU is now covered with a ragged crust of Lecanora, from which 

 protrude here and there weak branches of Empetrum, MyrtiUus, or Ledum, or 

 isolated leaves of Rvhus. Different stages of this course of development can 

 often be found close to one another or at different elevations on the side of 

 one and the same hummock. On the coast, the transition of living Sphagnum 

 to lichen crust often seems to take place in a very short time, so that neither 

 imder-shrubs nor fruticose lichens are able to attain to their usual abundance. 

 On the other hand, small liverworts become of greateven if passing importance." 



Warming (1890) found in the marshy regions along the east coast of the 

 North Sea that: 



Zostera filtered out and retained the fine particles of soil in the deeper water, 

 resulting in the formation of mud banks, while algae and Salicornia herbacea 

 fiUed the same oflB.ce in shallow water. As the ground became higher and 

 drier, Glyceria replaced Salicornia, and was accompanied by Triglochin, 

 Suaeda, Planta^o, Glavx, Atriplex, etc. ; this vegetation was then in its turn 

 driven out by Juncus, Hordeum, Festuca, Lepturus, Armeria, Artemisia, etc. 



Warming (1891) also traced the building of dunes on the Danish coast and 

 the development of vegetation upon them: 



The mobile dimes begin simply as heaps of sand formed by tides, waves, and 

 wind, the particles of which are as a rule less than one-third of a millimeter in 

 diameter. The further ^owth of such dunes is made possible by sandbinders, 

 Psamma arenaria, Elymus arenarius, Carex arenaria, Agropyrum junceum, 

 Alsine peploides, etc. The last two are found only on the lower dunes, and 

 are sooner or later driven out by Psamma and Elymus, which are especially 

 adapted to the building of high dunes, because of their ability to push up 

 through a cover of sand. Other plants, algse, lichens, and mosses, and low- 

 growing spermatophytes, find their way in among the shoots of Elymus and 

 Psamma, and, as the sand becomes more and more fixed, slowly conquer the 

 intervening spaces. The dune gradually becomes more stable, and is finally 

 spread with a thick, low, gray-green cover, before which the two original sand- 

 binders disappear. Finally, the stable dune may pass over into a stable 

 Calluna heath. 



