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The mountai regions of Lapplandsnow-breaks up into patches of heath alternatingwith frost scars or solifluction soils destitute ofvegetation or covered with a coat of lichens,hepatics and small mosses. This is a substitute forthe thick humus-producing mat of mosses commonas bottom layer in the low-alpine heaths.Among the ligneous plants of the low-alpine beltthe nanophanerophytic (Du RIETZ 1931, p. 46)shrubs (e.g. Salix lapponum) and the macrochamaephyticdwarf shrubs (e.g. Betula nana,V accinium myrtillus) do not ascend into the middlealpinebelt where mesochamaephytic dwarf shrubs(e.g. Cassiope tetragona) and inicrochamaephyticdwarf shrubs (e.g. Cassiope hypnoides, Salix herbacea)are the only to occur.The majority of the silvine plants that ascendinto the alpine area cease in· the low-alpine belt.A few actually occur throughout the vegetationalbelts of the mountains, viz. Lycopodium selago,Festuca ovina, Vaccinium vitis-idaea, Antennariadioeca. The middle-alpine belt, at least, is reachedalso by Rubus chamaemorus and several others.As compared to conditions in the low-alpine beltthe number of species in the middle-alpine vegetationis diminished, the latter being composedchiefly of the hardier among the alpine plants. Innorthern Lappland Cassiope tetragona plays animportant part in the vegetation of the middlealpinebelt. Likewise abundant in this area, butabsent farther southwards, are the grasses Hierochloealpina and Calamagrostis lapponica. In theother parts of Lappland the heaths of Cassiopetetragona are substituted by grass-heaths usuallydominated by J uncus trifidus and Carex Bigelowii.Abundant are also such species as Luzula arcuata(sens. lat.),- Festuca ovina, Poa alpina, P. arctica,P. alpigena and Deschampsia alpina. On wet slopes,where solifluction is always intense, microchamaephyticcreeping or suboliferous dwarf shrubs such asCassiope hypnoides and Salix herbacea, respectively,are important. On calcareous soil Dryas octopetala,a creeping dwarf shrub, is abundant also in this belt.Other low (mesochamaephytic) creeping dwarfshrubs occurring as high up as the middle-alpinebelt include Empetrum hermaphroditum, Arctostaphylosalpina, Phyllodoce coerulea and Loiseleuriaprocumbens. The two last-mentioned are not true6-652151 APhs 50creeping dwarf shrubs but rather semi-sedentary(cf. Du RIETZ 1931, p. 65).On calcareous soil the middle-alpine flora maysometimes be fairly rich. Low but nicely floweringherbs such as Silene acaulis, Saxifraga oppositifolia,Erigeron humile ( = unalaschkense), E. uniflorum,Campanula uniflora, Pedicularis flammea and othersare the adornments of this vegetational belt. Manyrare species of our mountain flora are to be foundon calcareous solifluction soil in the middle-alpinebelt.The change from low-alpine to middle-alpinevegetation corresponds to a marked climatic deteriorationappearing above the levels of about 1000-llOO m. In the middle-alpine belt and still higher,snow may fall and even remain on the ground fora few days at any time in the summer, and thefinal snow and frost come early in the autumn.As high winds usually follow the autumnal snowfalls,a pattern with bare patches results, where theground will soon become frozen. For long periods inspring and early autumn each day brings about afreeze-thaw cycle in the soil, causing a pronouncedfrost action that to a great extent determines thevegetation pattern of the higher belts. Intensecongeliturbation limits the vegetation to consistof an assembly of species adapted to exist on anunstable substratum and-beside the reducedproductivity-prevents the establishment of closedcommunities. This leads to a lower degree ofcompetition, and rare alpine plants, supposed notto endure competition, are often restricted tosolifluction soil on calcareous ground, e.g. Luzulaarctica, Sagina caespitosa, Papaver radicatum ssp.hyperboreum, Draba alpina, D. crassifolia, Campanulauniflora, Pedicularis flammea.The high-alpine belt or Regio alpina superiorAlthough the vegetation of the middle-alpinebelt is clearly distinguished from the vegetationof the belts above and below it, its limits are diffuse.With increasing altitude the patches of heathv-egetation are diminished and in northern La pp land(Torne Lappmark) they generally cease at about1200-1350 m, occasionally at 1400 m (Du RIETZ1925 f). The corresponding altitudes in southernLappland (Asele and Lycksele Lappmark) are.Acta Phytogeogr. Suec. 50