SCIENCE-GOSSIP. 



ORIGIN OF ARCTIC PLANTS IN BRITAIN. 

 By G. W. Bulman, M.A., B.Sc. 



A MONG the most interesting relics of the Glacial 

 period are some rare Arctic plants widely 

 dispersed on the higher mountains of Wales, the 

 Lake district and Scotland. These are supposed 

 to have come south with the ice, and when 

 temperate conditions returned to have been left 

 stranded on a few of the higher hills to become 

 witnesses of the glacial conditions which led them 

 from their northern home. Among them may be 

 mentioned Lloydia serotina, of the mountains of 

 North Wales ; Potentilla sibbaldia, of the Scottish 

 Alps ; Dryas octopetala, of the limestone heights of 

 Britain and Ireland ; Saxifraga nivalis, of the 

 mountains of the Lake district, Wales, the High- 

 lands ; and others. Certain of them occur again on 

 the Swiss Alps and the Himalayas, but are absent 

 from the intervening lower ground. They are 

 found also in the Arctic regions, which is supposed 

 to be their native home. 



How was this Arctic flora able to migrate to 

 Britain ? There are two suppositions regarding 

 glacial Britain. One is that it was a cluster of 

 low-lying, ice-covered islands, formed by what are 

 now the higher parts of the country ; the other, 

 that it was joined to the Continent by elevation 

 and had a land connection with the Arctic regions. 

 The latter gives the easier solution of the problem 

 of the migration of these Arctic plants southwards ; 

 indeed, a land connection seems almost necessary 

 to enable them to reach Britain. This was the 

 opinion expressed by Prof. Forbes in his " Fauna 

 and Flora of the British Islands," where he 

 remarks, " I cannot but think that so complete 

 a transmission of that flora as we find on the 

 Scottish mountains was aided, perhaps mainly, by 

 land to the north, now submerged " ( 1 ). 



At the same time he held the view that glacial 

 Britain was merely a group of islands in an Arctic 

 sea. He continues : " Now it was during this (the 



Glacial) epoch that Scotland and 



Wales and part of Ireland, then groups of islands 

 in this ice-bound sea, received their Alpine flora 

 and a small portion of their fauna. Plants of sub- 

 arctic character then would flourish to the water's 

 edge" ( 2 ). 



He suggests " transportation on floating masses 

 of ice." It is, perhaps, a little hazardous to offer 

 an opinion as to whether plants could migrate 

 across an ice-bound sea. Currents might carry the 

 seeds across the intervening waters. Prof. Forbes' 

 masses of ice might do something ; but if the land 

 to which they were being carried was covered with 



(1) Mem. Geol. Surv., i. p. 399. 

 ( a ) Ibid. p. 345. 



ice down to the water's edge it is difficult to see 

 how they could effect a landing. It can, however, 

 be supposed that seeds were drifted across before 

 glaciation had proceeded so far as to present the 

 barrier of an ice-bound coast. 



That the forms common to Britain and the 

 Arctic regions migrated southwards during the 

 Glacial period is the usual explanation ; but the 

 alternative view, that they have migrated north- 

 wards from temperate regions, seems worthy of 

 consideration. There is one fact in Arctic botany 

 which favours this latter supposition. Out of the 

 whole Arctic flora only one genus, Pleuropogon (with 

 one species, P. sabine) and seven species of other 

 genera are peculiar to the Arctic regions. The rest 

 all occur in temperate climates. This suggests that 

 the common forms migrated to rather than from 

 the north. 



Again, the present system of ocean currents 

 renders more probable a transference of seeds of 

 British plants to Arctic lands than of seeds of Arctic 

 plants to Britain. The Gulf Stream passing along 

 our western shores must at times receive vegetation 

 drifted down our westward flowing rivers, and carry 

 it on towards the North Pole. That this is possible 

 is well illustrated by the recently recorded discovery 

 of a drifted seed of the tropical Ipomea tuberosa in 

 the Hebrides ( 3 ). It is also well known that by the 

 agency of the Gulf Stream large quantities of drift 

 wood are heaped up on the shores of Spitzbergen 

 and other Arctic lands. The colder currents from 

 the north passing beneath the Gulf Stream would 

 not transfer Arctic species to Britain. 



Apart from such considerations as these, the 

 most natural explanation of the distribution of 

 those plants confined to isolated summits of lofty 

 mountains is the supposition that they have 

 migrated from the Arctic regions. It is otherwise 

 with certain widely distributed forms common to 

 Arctic and temperate lands. Thus, Armeria vulgaris, 

 occurring on hill-tops and mountains, is also dis- 

 tributed round our shores at the sea level as 

 far south as Cornwall, and ascends some of our 

 rivers. Cochlearia groenlandica has a similar distri- 

 bution. Taraxicum officinale, another Arctic plant, 

 is found everywhere. The distribution of these 

 and many others is more easily explained en the 

 supposition that temperate regions were their 

 original home. Indeed, when we examine the 

 actual distribution of the first-mentioned Arctic 

 species, we find that it cannot entirely be explained 

 by migration from Arctic lands during glaciation. 



(3) " Annals of Botany," vol. vi. p. 369. 



