328 RIKARD STERNER 



explanation of the distribution of the steppe species: the isolated occurrences 

 should be looked upon as relics from an earlier and more even distribution. Our 

 knowledge of the post-glacial history of the country lends support to such an 

 opinion (see e. g. the summaries in the work of i> Deutsche Geologische Gesell- 

 schaft>-> 1 910 and Hausrath 191 1). During the periods with more continental 

 climatic conditions the species have had occurrences that have more or less 

 closely connected the present isolated ones'. 



Even if isolated occurrences of steppe species generally find their real explana- 

 tion in this circumstance, we must not leave out of consideration the fact that, 

 thanks to a long-distance dispersal (even nowadays) certain species have been 

 able to reach isolated suitable localities. 



Samuelsson (19 10, pp. 480 ff.) holds that the peculiar isolated occurrences of 

 Gypsophila fastigiata in Eennoscandia should be explained as the result of a 

 long-distance dispersal. Another example of this, which may be of interest in 

 the sequel, is the occurrence on Riigen of Mulgedium tataricum, which is hitherto 

 scarcely found outside the steppes, a fact explained by several scientists on the 

 hypothesis that it has been brought thither in one of the great invasions of sand- 

 grouse in the middle of the 19th century. (Preuss, »Berichte d, Deutsch. Botan, 

 Gesellsch.», Bd. 27, 1909; Leick, »Mitteil. d. naturw. Vereins fiir Neuvorpom- 

 mern und Riigen», Jahrg. 48, 1921)- 



It would seem to be expedient not to imagine the power of long-distance 

 dispersal of species to be too narrowly limited. As has already been pointed 

 out, even very rare opportunities may be of great importance. 



In South Sweden there are number of interesting isolated occurrences of steppe 

 species. Most of these are found on Oland and Gotland, where of course 

 favourable conditions are offered to these species. There are also remarkable iso- 

 lated occurrences in Ostergotland in the country round Omberg (Oxytropis pi- 

 losa), in Falbygden (Stipa pennata), at Kinnekulle (Inula ensifolia), and in Skane 

 (for instance, Senecio integrifolius, Allium montanum, Asperula tinctoria, and 

 Carex obtusata). 



Many steppe species have their remotest North- West European occurrences 

 on Oland or Gotland: Adonis vernalis (Plate 14), Anemone silvestris (Plate 17), 

 Aster linosyris, Carex ligerica, Pulsatilla patens (note the occurrences in central 

 Norrland, in the parishes of Resele, Liden and Ramsele in Angermanland), and 

 Viola pumila; the strongly isolated occurrences on Oland and Gotland of the 

 Siberian species: Artemisia laciniata and rupestris and Carex obtusata, and the 

 occurrences of the Pontic species: Bassia hirsuta (Plate 13), Plantago tenuiflora 



' Under these favourable climatic conditions the species may also be supposed to have had greater 

 power of distribution through a better fructification. 



