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66 OLOF RUNEplants into low-alpine, meso-alpine and highalpinespecies.The different dwarf-shrub heaths of the lowalpinebelt were also studied by G. SAMUELSSON(1916, 1917).The efforts of these authors to construct vegetationalbelts according to distribution of plantcommunities were criticized by TH. C. E. FRIES(1917). He called attention to the fact that thevegetation of the lower parts of the alpine regionis very variable and declared the earlier divisionsof the alpine region to be founded on too roughgeneralizations. He moreover considered any divisionfounded on plant communities impossible.Instead, he tried a division on a floristic basis. Sothe lowest part of the alpine region, rich in "subalpine"plants, could be separated from the higherparts without them. FRIES considered the "subalpine"elements of the lowest part of the alpineregion to be relics from the Post-glacial warmperiod when the timberline was much raised. Hedivided the alpine region into two parts, viz. alpinaI (prima) and II (secunda). The first was dividedinto la and Ib, the limit being the above-mentionedancient timberline. The limit between I and IIwas drawn according to the beginning of the"boulderlands", i.e. the extensive fields of coarseboulders that cover large parts of the mountains athigh altitude. However, FRIES was not the first todivide the alpine region into two parts accordingto this criterion, for this was made as early as 1907by NILSON (KAJANUS) in connection with lichenologicalstudies in the Sarek Mts.The division of regio alpina according to the lowerlimit of the boulderlands was also used by SMITH(1920) and by TENGWALL (1920) who named thebelts regio alpina fertilis and regio alpina sterilis.As pointed out by Du RIETZ ( 1925 /) the limit ofthe boulderlands is geological and should not beused as a phytogeographical boundary. Instead, hepointed out the change in vegetation occurringclose to this level and caused by the replacementof the uppermost other dwarf-shrub communitiesby Salix herbacea communities. In 1930b hepublished a diagram showing the vertical distributionof vegetational belts in the Alps and Scandinavia.Having studied these questions mainly inActa Phytogeogr. Suec. 50Torne lappmark and in . Jamtland, Du RIETZ(1928, 1930a and b, 1942b and c, 1943, 1950e, 1964)finally presented the system of distribution of Swedishmountain vegetation, now current amongScandinavian phytogeographers. Like Central Europeanphytogeographers Du RIETZ distinguishes thealtitudinal regions from horizontally extendedregions by using the term belt (Stufe, etage, etc.).Thus Du RIETZ divides the Swedish mountainvegetation into five belts, viz. (1) the coniferousforest belt or the conifer belt (without oak), (2)the birch forest belt (the birch belt) or the subalpinebelt, (3) the low-alpine belt, (4) the middlealpinebelt, and (5) the high-alpine belt.Although since some thirty years this divisionhas been commonly used by Swedish phytogeographerssome divergences have also been presented.Thus, SELANDER (1950a) cut out the middle-alpinebelt that he considered indistinct in the calcareousareas of SW Lule Lappmark.G. BJORKIVIAN (1939) introduced a regio alpinadescensa to cover the woodless heath or meadowcommunities rich in alpine plant that occur alongsome of the lake shores in the uppermost coniferbelt or the subalpine belt. SELANDER (1950a, p. 45)however found it to be an unnecessary terminologicalburden "to retain the term regio alpinadescensa in order to designate an essentially localphenomenon".DELIMITATION OF THE MOUNTAINOUS AREA.­Much attention has been paid to the upper limits ofvarious vegetational belts, whereas the lowermostoccurrences of the vegetation typical of these beltshave been much overlooked. Thus our knowledgeabout for instance the delimitation of the mountainousarea is rather scarce. As the mountainrange decreases in height only gradually or irregularlytowards east and moreover is splitted byvalleys, a topographical boundary of the mountainousarea is difficult to determine. The onlydelimitation available at present seems to be thegeological border between the Caledonian Palaeozoicoverthrust nappes and the subjacent Pre­Cambrian rocks (cf. "Lappland east of the mountains").The geological boundary correspondsclearly to floristic and vegetational differences due