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160 TOM FLENSBURGrium are also represented by a very large numberof species in Kavsjon, but in contrast to Cosmarium,the majority of Closterium species are also foundin relatively rich fen in other parts of the mire.This is also true of the genera Euastrum and Micrasterias,except for a few species bound to lakes,e.g. E. gemmatum and M. mahabuleshwariensis.Of the partly planktic genus Staurastrum, manyspecies were found only in Kavsjon. There are afew cases, e.g. S. tohopekaligense, when a species wasfound in one of the many samples from Kavsjon,but since then never observed. Such stray findsmay be caused by chance dispersal of spores. Widedistribution due to easy long distance dispersalcould be inferred from the many exotic names givento desmid species found later in Europe. But onlywhen environment is favourable, does the dispersalof spores lead to lasting establishment.Leaving Lake Kavsjon for other parts of themire, one will nowhere find a similar multitude of. species among the benthic microphytes, not evenin the -richest fen areas. There are two areas with amicro-vegetation comparatively well developed asto number of species. One is the quaking fen thatwas formed from the southernmost part of LakeKavsjon after 1840. The other is the very large"soak" Bladopet that crosses the south-central partof the mire. In both, pH is generally 5.5 to 6 butin the middle of Bladopet it reaches 6.5. On anaverage, the electrical conductivity is lower thanin Kavsjon. The macrophyte vegetation is similarin the two areas, Bladopet and the quagmire, withSphagnum spp. predominant (moderately rich fen,at the most, in the system of Du RIETZ, opp. cc.).Despite different situation, hydrography and historyof development, this gives the two rich fenareas much in common as environments of microvegetation.Starting again with the desmids, one finds about100 species in each area (about half the number forKavsjon). The reduction, as stated above, is moderatein Closterium and stronger in Cosmarium,which genus is not so well-represented in Bladopet.Diatoms and other algal groups show a similardecrease in number of species. The desmid speciesfound in Bladopet and the quagmire nearly alwaysoccur in Lake Kavsjon, too, with the exception ofonly a few species that are more typical of poor fen,and consequently believed to avoid the higherelectrolyte concentration, or perhaps likely to beeliminated by the stronger competition in Kavsjon.In this group belong, for example, Euastrum crassumand Xanthidium armatum, as well as M icrasteriasJ enneri (only in Bladopet).A different matter is the great number of individualsof certain algal species ( Eunotia, Pinnularia,etc.) occurring in some of the samples from Bladopetand the quagmire, a feature that is frequently foundalso in the poor fens and even in the open bog area.A typical poor fen, such as Svartekarr, south ofthe quagmire, shows only 35 desmid species, andthe side-soaks of Bladopet (pH between 4 and 5)even less. Beside more or less eurytopic species,there are typical poor fen species (e.g. E1tastruminsigne and Xanthidium armatum) but also speciescommon to poor fen and open bog (e.g. a Tetmemorusof the Brebissonii group, and Penium spp.) .The open bog areas, which occupy the greaterpart of the mire, are well separated from Bladopetand its side-soaks, being on the ombrotrophic sideof THUNMARK's (1942) mineral soil water limit, orthe limit of indicators of mineral soil water accordingto Du RIETZ (1954b, cf. also 1949a, etc.). Thehighly specialized macrophyte vegetation of bogs isdealt with in this book by MALMER (see also M.1962a and b); on the Store Mosse there are manywet hollows with a pH of 3.8 to 4.2 and a characteristicalgal vegetation exceedingly poor as to thenumber of species, only 31 in all, which is less thana tenth of the number found for Kavsjon. The 15desmids present in bog hollows only rarely have awide amplitude (Cylindrocystis Brebissonii, Xanthidiumantilopaeum var. laeve); the majority areabsent from rich fen, e.g. N etrium oblongum (which .replaces the N. digitus of rich fen), Penium polymorphum,P. silvae-nigrae and the Tetmemorus mentionedabove. There are only 6 diatoms in the widebog area. They are all eurytopic, and some of themare highly gregarious, as mentioned above a featurerarely seen in the rich fens. Among other algae,the violet-coloured filamentous zygnemal speciesZygogonium ericetorum is omnipresent in the boghollows and can reach mass development..Acta Phytogeog1·. Suec. 50