Arctic Plants: Geographical Distribution 119 b 



The fact that the genus Primula is not a northern but a southern type, 

 best represented in the mountains, notably in the alpine region of temperate 

 Europe and Asia, seems to indicate that the few arctic representatives of the 

 genus are remnants of a glacial flora, now partly exterminated, or at least dis- 

 connected. 



Of the arctic Primulaceae the genus Androsace is the most widely distributed. 

 A. Chamaejasme is almost circumpolar, being absent only from Finmark, Spitz- 

 bergen, and Greenland; with regard to A. septentrionalis, this occurs. in Finmark 

 but is absent from arctic Siberia. Farther south these species have also been 

 recorded from the Alps of Switzerland, from Caucasus and Altai, and from 

 the Rocky mountains from Alberta to Colorado. 



However, the genus is relatively poorly represented on this continent, by 

 four species according to Gray, but more recently some three or four more have 

 been described and generally accepted. In the Alps of Switzerland, however, 

 the genus culminates with thirteen species; furthermore, seven species are known 

 from Caucasus, eight from the Altai and Baikal mountains, eight from eastern 

 Siberia, five from Ural, etc. It would thus appear as if the actual centre of the 

 genus must be sought in the Alps or in the Altai mountains. The three sections 

 which have been established of the genus viz. : Aretia, Chamaejasme, and Haplor- 

 hiza, are all represented in the Alps, but the first of these, Aretia, is not credited 

 to the Baikal and Altai mountains; it is known, however, from eastern Siberia. 



With regard to the development of the genus Androsace it deserves attention 

 that even if the European Alps may be considered a most important centre 

 owing to the larger number of species, including several endemic, then the 

 Rocky mountains must, nevertheless, constitute another, and of no smaller 

 importance. It is true that the genus in the Alps is accompanied by a close ally, 

 the monotypic Aretia, an ally so close that several authors have united it with 

 Androsace, but on the other hand we have on this continent an ally, Douglasia, 

 with four species, which is also closely related to Androsace. In other words, the 

 actual presence of these two genera on our continent seems to indicate that the 

 Primulaceae have also had a centre of development in America. And the dis- 

 tribution of Douglasia speaks in favour of this supposition. 



Douglasia nivalis Lijodl., D. montana Gr., andD. laevigata Gr. are natives of 

 the Rocky mountains and the Cascade mountains, principally at higher eleva- 

 tions; D. arcizca Hook., on the other hand, is known only from the arctic seashore. 

 In other words, these two genera, being arctic or alpine, may well be considered 

 as representing a high-northern centre of the Primulaceae. Douglasia arctica 

 being a truly arctic type, and Androsace Chamaejasme being quite common on 

 the arctic shore, including the archipelago, and sometimes accompanied by A. 

 septentrionalis and A. Gormani Greene, this little alliance may indicate a former 

 centre located in the polar regions; moreover, we remember that A. Chamaejasme 

 is almost circumpolar. 



The present more advanced development of these two genera farther south 

 in the Rocky mountains may have had its origin from an arctic centre. The 

 fact that both A. Chamaejasme and A. septentrionalis are known also from the 

 Altai and Baikal mountains indicates that they came from the north. In 

 Europe these same species migrated as far south as to the Alps and even to 

 Caucasus, where they are still in existence. The approximately circumpolar 

 distribution of A. Chamaejasme in connection with the exclusively arctic one of 

 Douglasia arctica thus seems to illustrate an instance of a single centre being 

 located in the arctic regions, although the genera in question are at present more 

 amply represented farther south, the former in mountains as remote as the 

 Alps, the Altai, and the Rocky mountains. But with regard to the other species 

 of Androsace, these must have originated in the south, the Alps and the Altai 

 mountains, since none of. these show any evidence of having existed farther 

 north, at least not in the polar regions. 



