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158 NILS M.ALMERnounced mire margin character may be mentioned.Under a tree and shrub layer of Alnus glutinosa,Betula pubescens and Salix spp. tall herb speciessuch as Crepis paludosa, Filipendula ulmaria andGeum rivale grow together with Carex appropinquata,0. caespitosa and Calamagrostis neglecta.Among the mosses of the well-developed bottomlayer Calliergon giganteum, Calliergonella cuspidata,Campylium stellatum, Climacium dendroides andMnium spp. may be mentioned. Especially wherethe tree layer is sparse, additional fen plantsgrow, e.g. Caltha palustris, Galium uliginosum,Epipactis palustris, Parnassia palustris, Car ex echinata,C. hostiana, C. nigra, C. panicea and Eriophorumlatifolium. If these parts are not too wet,Aulacomnium palustre, Sphagnum parvifolium, S.teres, S. warnstorfianum and Tomenthypnum nitensmay characterize the bottom layer.Regional aspectsThe regional differences in the mire vegetationfollow the general plant geographic pattern inSouth Sweden (see the author's paper "The southvo:esterndwarf shrub heaths", in this volume). Thedistribution of the rich and poor fen vegetationvery well reflects the distinction between areaswith calcareous soils chiefly in the lowlands andthe silicious areas mainly in the uplands. In all thevegetation types there are some differences betweenthe southern and northern parts. It is, however,hardly possible to find any indications for a mainregional boundary in the mire vegetation resemblingthe southern and western limit of Picea abies whichseparates the Nemoral and Boreo-Nemoral zones(see "Forest regions" by SJORS). Especially in thebog and poor fen vegetation larger differences aremet with between the western and eastern parts,partly corresponding to the floristic Erica tetralixlimit (see the paper about the heaths). In the bogvegetation, regional subformations and allianceswere distinguished by Du RIETZ (1925c, p. 22,1949a, 1950a, b, c). Cf. also Osv.ALD (1925b, pp.101-103). They reflect the differences in humidityfound in the South Swedish climate. The intensersummer drought in the eastern parts seems to favourthe development of wooded bog vegetationthere (M.ALMER 1962a, p. 219). In addition to thisand to other hydrological differences there are alsodifferences in the concentrations of Na, Mg and Clin the water (WITTING 1947, 1948, GoRHAM 1956,MALMER 1961), due to variable amounts broughtto the ground by airborne transport. Their importancefor the vegetation is somewhat obscure, butthere may be other effects of similar differences, e.g.in K, N and S, not yet investigated.Even though many plant ecologists have studiedthe South Swedish mires, it is still only possible toindicate the general framework of the variation intheir vegetation. This paper is too short to permita complete discussion, but the reader may be referredto several detailed works cited above. In manycases, however, there is an urgent need for thoroughstudies both concerning the plant commun.ities andtheir habitat conditions. The fundamental worksof Du RIETZ constitute a good starting point forfurther sociological investigations. In South Swedenthere are still several undisturbed or not seriouslydisturbed mires representing types which to-dayare very rare on the European continent. Swedishplant ecologists have an international responsibilityfor the protection and investigation of these mires.Acta Phytogeogr. Suec. 50