THE CONTINENTAL FLORA OF SOUTH SWEDEN 309 



Rocky Escarpments. The natural occurrences of steppe species in the Archaean 

 rock districts of South Sweden might be supposed to have been made possible 

 also through southerly exposed precipitous cliffs. The great supply of light 

 and heat, as well as the absence of species more fit for competition, make these 

 cliffs favourable to steppe species. Great parts of the South Swedish Archaean 

 rock country are much broken and rich in southerly exposed rocky escarpments. 

 This is especially the case in north-eastern Smaland, Ostergotland and Soder- 

 inanland, western Vastcrgotland, northern Halland, and northern and central 

 Dalsland. (See p. 343.) 



Nevertheless the escarpments are not so important as might be expected for 

 the distribution of steppe species. Only the distribution of a few species is 

 determined by the occurrence of rocky escarpments. Probably the reason is partly 

 that the rock ground is unsuitable for many species; partly that most steppe species 

 in South Sweden occur as calciphilous species and may thus not thrive on the 

 non-calcareous Archaean rock-ground; and lastly that the cliffs are generally so 

 strongly isolated that species furnished with less effective power of dispersal 

 cannot utilize all suitable localities. Later on, in treating another group of species 

 (Chapter x), I shall have an opportunity of giving a more detailed account of the 

 importance of the rocky escarpments for the distribution of species in South Sweden. 



The steppe species that occur to a greater extent on those localities are only 

 Allium montanum (Plate 6), Potentilla rupestris (p. 326), Melica ciliata (Plate 10), 

 Veronica spicata (Fig. 7), and Artemisia campestris (Plate 5). As regards Ve- 

 ronica spicata, it has the greater part of its occurrences in Ostergotland, Tjust 

 and Sodermanland on rocky escarpments. 



Poa bulbosa besides appearing on sand-fields and rock-pavements in eastern 

 Skane and Oland and Gotland, has a small number of probably spontaneous 

 occurrences on cliffs in the coast regions of Smaland, Ostergotland and southern 

 Sodermanland, and in this respect it coincides with Melica ciliata. 



On the great arable fiat regions of South Sweden, especially in the Malar- 

 district, there are smaller uncultivated areas scattered about, which partly 

 form rocky hillocks. The hollows and crevices in the ground of these 

 hillocks being filled up by deposits of clay, sand or gravel there are in these 

 places many suitable localities for a herbaceous hillside vegetation. To a great 

 extent, however, these are rendered possible by the cutting down of a shading 

 woodlayer. A natural occurrence of steppe species in the localities mentioned is 

 not to be excluded; however, it is impossible to judge in what degree this may 

 be the case. The abundant distribution of many steppe species in these regions 

 will be treated later on (pp. 314 ff.). 



