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the water below the surface is poor in oxygen inSchoenus fens, while the water in the Cratoneurumfens is considerably richer.The southern mires 157One type of rich fen vegetation, the Magnocaricion,characterized by tall, in some cases tussockformingcyperaceous species, holds a rather uniqueposition. Usually only one species predominatesove large areas, accompanied only by scatteredindividuals of other species. A high water tableand shading and abundant litter from the highproductivefield layer prevent the formation of abottom layer and the invasion of more species. Bymost Continental European plant sociologists theMagnocaricion vegetation is treated with the reedvegetation in the order Phragmitetalia (KocH 1926,OBERDORFER 1957). Most Swedish authors, however,include it in the mire vegetation.Though some of those communities which aredominated by Carex lasiocarpa or Carex rostrataare to be placed in the poor fen vegetation, the bulkof the Magnocaricion communities belongs to therich fen vegetation. The most common dominantsare C. acuta, 0. elata, C. paniculata (mainly inSkane), C. riparia and C. vesicaria. Especially onFig. 6. Ophrys insectijera growing in Schoenus jerrugineusthe Baltic Islands and in northernmost U pp land rich fen with percolating water. To the left GymnadeniaOladium mariscus is abundant, usually outcrowdingeverything else.belong to Sesleria coerulea. North Gotland, Hall, Hasselriv.conopsea var. densijlora (bud stage). The long strawsTypes of Magnocaricion grow along lake shores July 2, 1938. Photo Bengt Pettersson.and riverbanks (lower and middle geolittoral accordingto Du RIETZ 1940) in the calcareous areas. mocks are invaded for instance by Calamagrosti8Caltha palustris, Galium palustre, Lythrum salicaria, canescens and by bryophytes, e.g. CalliergonellaMenyanthes trifoliata, Mentha aquatica, etc., are cuspidata, Oampylium stellatum and M nium rugicum(T. KARLSSON, unpu bl.).intermingled (Du RIETZ et al. 1939, STALBERG1939, HoRN AF RANTZIEN 1950, ALMESTRAND &LuNDH 1951). In the Carex elata vegetation on such As the rich fen vegetation is most common insites HoRN AF RANTZIEN (1951) distinguished a the agricultural districts the localities usually havepoorer type with Carex diandra and Drepanocladus been more or less intensely affected by grazing.exannulatus and a richer kind with Carex appropinquataand Scorpidium scorpioides. On secondary anything like the original state (if there has beendrainage and even cultivation. Rather few are inlocalities, such as abandoned peat-hags and shores one since the N eo lithic age), while there is a bulkof partly drained lakes, there occur two successional of semi-natural vegetation which is often unstablestages. In the first, such species as Hydrocharis and difficult to interpret but may comprise severalmorsus-ranae, Lemna spp., Utricularia vulgaris and distinct types. Further the delimitation of the fenCalliergon giganteum grow between the hummocks. vegetation from related but meadow-like vegetationis difficult.They are absent in the second stage, when the spacebetween the hummocks is filled up and the hum- Among these confusing types one with a pro-.Acta Phytogeogr. Suec. 50