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100 VILHELM GILLNERmay be considerable. Significantly enough it increasesespecially during the latter part of the vegetationperiod, when the weather normally growsmore stormy and gives rise to high water.Fig. 2. Salico1·nia europaea and Suaeda maritima on extremelysaline soil in the upper geolittoral. The smallheaps of soil have been thrown up by a sand-dwellingbeetle, Bledius furcatus. Between the heaps bright patchesshow incipient crystallization of salt. Halland, landwardside of the island Vallda Sando. July 3, 1958. PhotoV. Gillner.bears the mark of agriculture. The thickets anddeciduous forests that must once have stood whereverthe substrate was suitable have now mostlybeen replaced by fields or meadows strongly affectedby farming. Nevertheless it seems as thoughthe salt marsh associations described above arenatural ones, for the salinity of the soil preventsthe immigration of ligneous plants into these habitats.Investigations have confirmed that the salt contentin the substrate of Salicornietum strictae isconsiderable. During late spring and early summerthis association is for long periods beyond the reachof the sea and a good deal of evaporation takesplace. As a result the salinity of the rhizosphereincreases at this season and may be higher thanthat of the sea. In Puccinellietum maritimae thissalinity shows slighter variations, being about thesame as _that of the seawater. This can be explainedby the fact that the vegetation is closed and preventsevaporation from the soil surface. In JuncetumGerardi as a whole the salt content is lower,but even in parts situated high up on the shore it"SALT DESERTS".-Where salinity is excessivebare patches may be found in shallow depressionsin the elevated parts of the salt marsh. During thedroughts of early summer these may be white withsalt crystals-salt deserts in miniature. They arefringed by a Salicornietum europaeae composedsolely of Salicornia europaea and Suaeda maritima.Both tolerate considerable salinity and are hererepresented by short individuals, towards late summercharacteristically red in colour. In contactwith these pioneers is a Puccinellietum maritimaein the form of a subassociation with Salicorniaeuropaea. This vegetation, always open and low, isrestricted to decided halophytes. Competition isfeeble, and, besides Salicornia europaea, Halimionepedunculata has a chance to assert itself. The communityis in its turn adjoined by a Juncetum Gerardi,first in a strongly halophytic subassociationwith Salicornia europaea, more peripherally in anotherwith Oentaurium. The latter harbours Oentauriumpulchellum, C. vulgare, Sagina nodosa etc. Thebottom layer is ade up of mosses such as Amblystegiumserpens, Bryum salinum, Oampylium polygamumand especially Pottia H eimii. Cyanophytes,too, are plentiful thanks to the open vegetation,and Rivularia nitida is together with Pottia H eimiiespecially characteristic of the association.The vegetation around the salt desert patches isexposed to a salinity greater than that of the seadue to salty subsoil water and a concentration ofsalt in dry weather. Around the salt deposits theassociations of the saline salt marsh are found, soto speak, in a translocated zonation.BRACKISH MARSHES.-Quite a different picture ispresented by salt marshes exposed to seepages offreshwater or brackish seawater. The hydrolittoralis inhabited by the association Scirpetum maritimi.This is also found in depressions in the geolittoral,where it is more exposed to grazing, however. Theassociation has only a few members, the nearlyfaithful species Scirpus maritimus and Se. Taber-.Acta Phytogeog1·. Suec. 50