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188 FOLKE BJORKBACKmixed with species better at home in poor fes, e.g.Sphagnum Jensenii,· S. Dusenii, S. Lindbergii, Cladopodiellafluitan·s and Gymnocolea inflata. Occasionalslightly drier cushions are formed by Drepanocladusbadius, Sphagnum subfulvum, etc.The larger part of the flark surfaces, the mudbottom areas, are however nearly devoid of bryophytesbut usually covered by a film of algae. Bubblesof oxygen (cf. above, regarding "corrosive oxidation")produced by their photosynthesis in fineweather are often visible below the slimy film.For unknown reasons the vascular plants of theflarks grow only sparsely. The list from each siteis usually short. Nearly always present are Eriophorumangustifolium, Carex limosa, C. rostrata andC. chordorrhiza, frequent also C. · lasiocarpa andC. livida. Other typical constituents are Droseraanglica (in the north mainly f. pusilla), Menyanthestrifoliata, Equisetum fluviatile, Juncus stygius,Eriophorumgracile, Utricularia intermedia, U. minor,in the south and lowland Rhynchospora alba, in thenorth-east Eriophorum medium and E. russeolum.OTHER FEN VEGETATION.-Large areas of wetmire are not actually differentiated into lawn-likeor mud-bottom communities. They may have anintermediate appearance, usually with Trichophorumcaespitosum dominant, having a tussockyhabit, or on sites that are often irrigated by highwaters, Carex lasiocarpa or C. rostrata. The tallgrowingCarex fens were used for haymaking inthe old days, but their production was often solow that hay could be mown only every second orthird year. To promote their yield, artificial irrigationwas used in many places. The best developedCarex fens grow alongside rivers, in the inlanddeltas, and on lake shores, including reeds of thesemiaquatic C. aquatilis (often replaced by C.acuta, chiefly at lower elevations), and tall tussockcommunities of C. juncella in the middle and uppergeolittoral.On slightly less soaked sites willow fens arewidepread, a striking feature of the upland andmountain valleys of northern Fennoscandia. Thegrey-leaved species Salix glauca and S. lapponumprevail, with the pure green of S. phylicifolia intermingled.The rich fen vegetation 'is not dealt with in thissection, as reference can be made to N ORDQVISTregarding the central upland and to A. PERSSONwith respect to the mountains.MIXED MIRE VEGETATION.-An excellent exampleis given by BJoRKBACK (below). Here it will besufficient to state that the fen component may haveany kind of floristic composition, ranging from poorfen to extremely rich fen, and that the extent towhich fen plants are able to survive on the "ribs" or"strings" is equally variable.ALGFLOARNA, A MIXED MIRE COMPLEX IN JXMTLANDBy Folke BjorkbackEnvironmental conditionsThe triangular northern part of the Cambro­Silurian area in Jamtland is one of several highlypaludified upland plains forming together a broadbelt to the east of the foothills of the Scandes.This flat area lies between Gaxsjo and Stromsund,about 70 km NNE of Ostersund. Characteristic landformfeatures are broadly shield-shaped hills orridges giving the horizon a gently undulating appearance,when visible at a distance. They are sepa-rated by plains, often with a slightly rugged microtopographydue to irregular deposition of the glacialtill.The bedrock consists of slate, greywacke orlimestone, the latter abundant in the eastern parts.Of acid rocks the Strom quartzite is quite widespreadnorth of Stromsund.Climatically this area is intermediate betweenthe subcontinental interior of Lappland and thesubmaritime more southern and western parts ofA.cta Phytogeogr. Suec. 50