academy ok sciences.] CENTERS OF DISTRIBUTION. 27 



and in the European Alps. E. alpinus L. shows about the same geographical distribution as 

 E. unifiorus L. in the north as well as in the south, and both are evidently of Arctic origin. A 

 genuine American type is. on the other hand, E. pinnatisectus (Gr.) Nels., which is confined 

 to the Rocky Mountains. Its near ally, E. compositus Pursh, is not infrequent in the aspen 

 zone of these mountains, and occurs also in Sierra Nevada, extending from there to the Arctic 

 seacoast and Greenland. 



Artemisia Norvegica Fr. 



In North America this species occurs in the Rocky Mountains from latitude 62° to south 

 Colorado and the Sierra Nevada, California. In Asia the distribution is given by Trautvetter 

 as: "Siberia arctica et orientalis, Mandshuria"; furthermore, it is known from Europe: 

 Mountains of Norway (Dovre) and Ural. The plant from Arctic Siberia, however, is not 

 A. Norvegica Fr. but a near ally, if not a mere variety; it is A. arctica Lessg., by Gray described 

 as var. Pacifica of A. Norvegica. Real A. Norvegica is thus a mountain plant which does not 

 extend to the Arctic Circle, which is totally absent from the European Alps, and which is not 

 a member of the Altai flora. 



The main center of distribution seems to have been in the Rocky Mountains on this conti- 

 nent, but not in Norway so far as concerns Europe. I am uncertain about the plant reported 

 from Ural. 



None of the European species of the genus are near allies of this, and A. Absinthium L., 

 A. vulgaris L., and A. campestris L. are the only ones known to occur in Norway. In North 

 America, on the other hand, Artemisia globularia Cham, from Alaska and adjacent island, 

 A. Richardsoniana Bess, from Arctic America, and A. Parryi Gr. from the mountains of Colo- 

 rado, may be looked upon as near aUies of this species. In addition to these several others are 

 inhabiting the same Alpine regions, viz, A. oorealis Pall., and A. scopulorum Gr. It seems, 

 therefore, natural that the species A. Norvegica has had its center of development in the Rocky 

 Mountains. The wide gap in distribution can not be explained satisfactorily, unless we sup- 

 pose that the species did have a much wider range before, but became exterminated in the 

 mountains between. 



Artemisia borealis Pall. 



Being circumpolar, and, furthermore, distributed from Colorado to Alaska and Labrador, 

 and finally being a member of the Altai flora, this species did undoubtedly originate in the 

 Arctic region. Migrating south during the glacial epoch, the species did not reach the Euro- 

 pean Alps nor Caucasus, but it evidently followed the Rocky Mountains, where it succeeded in 

 getting foothold, and where it is still persisting. 



Artemisia scopulorum Gr. 



This species is only known from the Alpine region of the Rocky Mountains in Colorado, 

 Utah, and Wyoming, where the center of distribution and of development naturally was located. 



THE GENUS ANTENNARIA. 



In recent years the genus has been studied very extensively on this continent, and Greene 

 deserves credit for being the first author to demonstrate that Antennaria plantaginifolia (L.) 

 Richards, as formerly understood, comprises several well-marked species. In the vicinity of 

 Washington, D. C, Greene segregated not less than five species: A. neglecta, fallax, decipiens, 

 neodioiea, and alsinoides, and by extending his study of the genus farther north, and especially 

 westward to the Rocky Mountains, this author discriminated a number of new species, the 

 majority of which are undoubtedly valid. Since then several other authors have commenced to 

 segregate species of the genus, with the result that Antennaria is now quite a large genus on 

 this continent. This seems very natural, considering the fact that the genus is very abundantly 

 represented in the lowlands as well as in the mountains, extending north to the Arctic region 

 and to the highest altitudes in the Rocky Mountains. In Europe and Asia the genus is very 



