Arctic Plants: Geographical Distribution 79 b 



Of these species the following are circumpolar : 

 Air a caespitosa Cardamine hellidifolia 



Catabrosa algida Arabis alpina 



Carex glareosa Saodjraga stellaris 



Luzula parviflora Campanula rotundifolia 



Salix herbacea Artemisia borealis 



However, the Hudson bay region, between 55° and 65° N. L., is quite rich 

 in arctic species, and of the about 450 species which are known from there, 

 about 90 are circumpolar, including those enumerated above. 



Most of these circumpolar plants evidently belonged to a flora, which in 

 tertiary times inhabited the polar regions, but was forced towards the south 

 during the glacial epoch. Many of these sought refuge in the higher mountains, 

 but returned to their northern homes when the ice receded. And on their retreat 

 to the polar regions they were accompanied by a number of southern, mainly 

 alpine, species; thus the present arctic, flora is also represented by a southern 

 element. However, the probability is that not a few of the circumpolar plants 

 remained on the southern mountains, some to persist, others to succumb. This 

 may be demonstrated by the indisputable fact that the alpine flora shows a 

 commingling of types similar to the present arctic flora. These foreign arctic 

 types are remarkably distinct, according to longitude, an American element 

 being represented in the arctic American flora, a European in the arctic European, 

 and a Siberian in the arctic Asiatic. For instance, the occurrence of the American 

 Astragalus aboriginorum in arctic America, the American Erigeron compositus 

 in arctic America and Greenland, etc. But it is merely conjectural to determine 

 the actual roads, followed by these plants from the polar regions to the south, 

 as well as on their retreat. And the difficulty culminates especially when we 

 bear in mind the extraordinarily scattered distribution of some of these polar 

 plants in southern regions, the higher mountains for instance. It is still more 

 difficult to appreciate the actual means by which the migration became effected. 

 Great importance has been attributed to the belief that migratory birds carry 

 with them seeds of plants, but recently we have learned that such birds migrate 

 on an empty stomach, and are almost always clean when they commence their 

 long journey. This statement we owe to Knud Andersen,^ who made the start- 

 ling observation in Denmark, that during a period of 4-5 years the intestines of 

 all the birds killed near the lighthouses were found to be empty, beside the fact 

 that no seeds were found adhering to any parts of these birds. However, Pro- 

 fessor Heru-y W. Henshaw ^ has, more recently, expressed an opinion which is 

 entirely different, making the following «tatement : 



"The sources of the vegetation and the means by which the seeds of plants 

 and shrubs were originally transported to these distant ocean-girt islands, 

 thousands of miles from the nearest mainland, are a most inviting field of specula- 

 tion. The winds are capable of conveying minute seeds to great distances, and 

 favourable ocean currents also materially aid as plant distributors. Birds, 

 however, are doubtless the most important of nature's seed carriers. Viscid 

 and hooked seeds attach to their plumage, or seeds may be carried in smears of 

 earth or mud on feathers, bill, or feet. Such seeds may be transported indefinite 

 distances and, once in a thousand years or so, dropped on soil favourable to 

 growth. The members of the most recent expedition to the island, the Nutting 

 party in 1911, were especially requested to examine carefully all their specimens 

 of Laysan birds for the presence of seeds, and actually found attached to the 

 foot of a Laysan albatross a seed of a species of the bean-caper famUy, which is 

 generally distributed in the South Sea islands. So far as known the plant does 

 not grow on Laysan, and had this seed chanced to fall in a favourable spot the 



' ^Compare C. H. Ostenfeld in Botany of the Faeroea. Part I, p. 117. Copenhagen, 1901. 



2 Henshaw, H. W. Our Mid-Pacific Bird Reservation. Yearbook of the Dept. of Agric. 1911. Wash- 

 ington, D.C. 



