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Calcareous fens in J iimtland 197FEN MARGIN VEGET.ATION.-Communities veryrich in species, especially in herbs, are often observedclose to mineral soil. Because of the presenceof a number of species not found in the typical"lawns" of the open expanses nor in the meadowfens, this group of communities is kept separateeven though they remind to some extent of themeadow fens. Some of the species typical of openlawns or meadow £ens are absent. A species con-.stantly found in the fen margin vegetation is Equisetumpalustre; it also occurs in spring vegetation.As mentioned above Oarex flava occurs in the marginalvegetation of the fens but 0. jemtlandica isnever met with. On Arasmyren the two speciesPolygonum viviparum and Oarex nigra are frequent.They also grow in the meadow fens. In all 29 herbshave been noted, among them for example Pedicularissceptrum-carolinum. In the bottom layer 20species have been listed, the most frequent dominantbeing Oampylium stellatum.SPRING VEGET.ATION.-This kind of vegetation isnot well developed in Arasmyren, probably becausethe springs are situated on the open mire expanse.Equisetum palustre is constantly found and somesprings are covered by cushions or carpets ofPhilonotis fontana, others being dominated by Oraton. eurum falcatum in the bottom la.yer. Richerspring vegetation occurs elsewhere, especially whenthe springs are situated on strong slopes or on theboundary between mineral soil and a mire.MAGNOCARICETA.-This kind of vegetation {cf.SJORS 1950b, p. 197) consists of tall cyperaceousplants and grasses. It is highly variable and occursin different kinds of habitat. A common featurefor them all is abundant seepage, at least at intervals.The peat is frequently mixed with mineralsoil, for instance along watercourses, and there maybe quite firm. But there are also continuous transitionsfrom magnocariceta to mud-bottom communitiesand to lawn-like vegetation. Both types oftransitions occur on Arasmyren. On the banks ofthe near-by river Ojan both magnocariceta andtransitions to meadow vegetation are extensive.Among frequent species on Arasmyren can be mentionedOarex acuta, 0. juncella, 0. rostrata, Deschampsiacaespitosa, Equisetum fluviatile and Filipendulaulmaria. The bottom layer which is oftenscanty contains such mosses as Oalliergon giganteumand species of M nium.CARPET-LIKE VEGET.ATION.-The "carpets" (SJORS1948a, p. 282, 1950b, p. 199) are nearly alwaysdeveloped as the Scorpidietum association (DuRIETZ 1949a, p. 304). This vegetation occurs inJamtland on wet slightly sloping fens with seepingwater (SJORS 1948a, p. 280), but it is more widespreadon almost horizontal parts of the fens.M enyanthes trifoliata, Oar ex limosa and 0. jemtlandicaare frequent species of the field layer, thelatter in fens very rich in lime. In less rich vegetation,0. jemtlandica is replaced by 0. livida.Occasionally, however, 0. jemtlandica may evenoccur in combination with Scheuchzeria palust1·is,as observed in the eastern part of the Hammerdalplain. Scorpidium scorpioides is always dominantin the bottom layer in which Riccardia pinguis isfrequently found.MuD-BOTTOM VEGETATION.-This type of vegetation(SJORS 1948 a, p. 282, 1950b, p. 200) occursmainly on slightly sloping or almost horizontalparts of the mires. Its species composition comesclose to that of the carpets. On Arasmyren Oarexjemtlandica is however rare in the mud-bottoms.Oarex chordorrhi-z:a is very frequent, and Utricula'riaintermedia is typical. Like the field layer the bottomlayer is generally sparse and may be totally absent.Scorpidium scorpioides is the most usual moss butother bryophytes are sometimes dominant, forinstance Oinclidium stygium.Flarks nearly devoid of macro vegetation (SJoRs1948a, p. 280, 1950b, p. 201) alternate with ridgesof hummock or bands of lawn-like vegetation mainlyon weakly sloping fen surfaces. The flarks areusually elongated with their long axis at right angleto the slope (SJORS 1946, 1961 b). They are waterfilledat intervals and precipitation of calciumcarbonate has often been observed, pH frequentlyexceeding 8. There is often a rich vegetation ofalgae in the water but unfortunately few investigationson the micro vegetation have been carriedout, the only published paper regarding Jamtlandbeing GRONBLAD (1963)..Ac·ta Phytogeog.1-. Suec. 50