320 RIKARD STERNER 



towards the east may also be judged dependent on the temperature conditions 

 in summer, which are very favourable in the east. The i6° C. July isotherm 

 which comprises large parts of South Sweden (see Fig. i, p. 256), travels 

 through Finland in a north-easterly direction not unlike the distribution limit of 

 Ranunculus polyanthemos. The general temperature conditions in northern Fin- 

 land during this season, schematically expressed in the position of the July 

 isotherm, are consequently hardly more disadvantageous than those of the same 

 kind in Central Sweden, i. e. the richest part of the distribution area of the 

 species in the Scandinavian North. It might be said, also, that, on account of the 

 favourable temperature conditions, the species has been able to utilize the sui- 

 table localities, suitable as to the nature of the soil, that exist in northern 

 Finland. 



The distribution areas of several other species belonging to the flora of the 

 South Swedish herbaceous hillsides, often forming important elements in it, stretch 

 along the coast to central Norrland and even reach some distance into the in- 

 terior, especially on the Jamtland Silurian district. Of herbaceous hillside species 

 with such a distribution we may mention Galium verum, Calamintha acinos (di- 

 stribution map in Andersson och Birger 191 2, p. 347), Arabis hirsuta (1. c. p. 339), 

 Saxifraga granulata, Pimpinella saxifraga, and Viscaria vulgaris. We have here 

 the northernmost outposts of the Baltic herbaceous hillside flora. 



Many South Swedish steppe species reach their northern limits on the Central 

 Stvedish plains. 



With regard to some species the limit in the eastern part of Central Sweden 

 pretty faithfully follows the northern limits of the arable land, for instance Arte- 

 misia campestris (Plate 5), Phleum Boehmeri (Plate 5), Polygala comosa (p. 316), 

 and Seseli libanotis (p. 334). 



It should be noted that even species of the South Swedish herbaceous hill- 

 side flora with a different general distribution in Europe have a similar northern 

 limit in Central Sweden, for instance the Western European Pulsatilla vulgaris 

 (Fig. 15) and the general Middle European Helianthemum chamaecistus 

 (Fig. 16). 



This northern limit would thus seem to be put in connection with the mode 

 of occurrence of species and the topograpJiy of the district. It is also of great 

 importance, however, that, thanks to the high lime percentage of the soil and 

 to the favourable climatic conditions, the Central Swedish plain districts offer the 

 species better conditions than the higher, hilly coniferous forest districts in the 

 north. It should be noted that a great number of South Swedish species with 

 a wholly different mode of occurrence have their northern limit in these parts, 

 for instance, Inula salicina (Plate 7), Serratula tinctoria, Pulmonaria obscura 

 (Plate 11), Selinum carvifolia (Plate 7), Chimaphila umbellata (Plate 12). 



