580 TRANSACTIONS OF SECTION K, 



seeds or edible fruits) belonging to the Atlantic, Lusitanian, and American ele- 

 ments, arrived by chance, and certain salt-marsh species by ocean currents. 



Mr. E. A. N. Arber expressed the opinion that the British alpines did not 

 come from the Arctic regions at all. The original home of the great majority 

 of British and European alpines was northern Asia, and the path of their migra- 

 tion was east to west, rather than north to south. He accepted the theory up- 

 held by some geologists that land connections existed between Great Britain and 

 Ireland, and also between England and France, both before and after the main 

 period of glaciation. 



Dr. C. E. Moss said it was a mistake to concentrate attention on the local 

 Lusitanian species of West Ireland and the south-west peninsula of England. 

 These plants are connected by many intermediate ones with certain other 

 Atlantic species which, so far as the British Isles are concerned, are limited to 

 the southern and eastern coasts of England. Limonium reticulatum, Suaida 

 fritticosa, Salicornia perennis, &c, are examples of such species. It seems 

 probable that they migrated from South Europe along the west coast of France 

 to the south-east of England, where they find their northern limits. No land 

 connections, no casual dispersal by wind or birds are needed to account for the 

 British distribution of these species ; for, being halophytes, their seeds are 

 doubtless capable of being carried by ocean drifts. The latter, having an 

 easterly trend, may account for the absence of these species from the west of 

 the British Isles. The distribution of these species is just as remarkable as that 

 of the Lusitanian plants, which belong to the same distributional type. 



Mr. G. Claridge Druce said he hesitated to accept the theory of the sup- 

 posed post-glacial land connection as an explanation of the occurrence of the 

 Lusitanian element in the Irish flora. The presence of the remains of the mam- 

 moth and hysena in post-glacial deposits (if indeed they were not pre-glacial), 

 was not more remarkable than the absence of the viper and the mole from the 

 Irish fauna. Nor had he heard from the upholders of this theory any sufficient 

 explanation of the great diminution of species in Ireland as compared with 

 England. There was no doubt that many plants could be widely dispersed by 

 birds and wind. As recent evidence of this, he cited the occurrence of Scirpus 

 maritimus in Berkshire, of S. Taberncemontana in Bucks and Oxon; and the ex- 

 traordinarily rapid spread of Crepis taraxacifolia over midland England in the 

 last twenty years. 



Mr. Clement Reid then replied. He said : The wide range of the discussion 

 and the late hour allow no time to deal with the various questions that have 

 been raised ; I would like, however, to return to the two main factors that 

 dominate the situation. If I am right, and in this I am only voicing the 

 opinion of all geologists who have studied the question, the glaciation and cold 

 were so intense that it was impossible for any of the higher animals or plants 

 to have survived in the greater part of Britain. In the South of England some 

 Arctic and North Temperate forms lingered ; but the surrounding sea was far 

 too cold for much else. 



The second factor is the extent of the connection with the Continent in post- 

 glacial times. As to this, we cannot speak with absolute certainty ; but all 

 the big rivers of England cut their post-glacial channels to about 90 feet below 

 the present sea-level, and the Cornish rivers, which flow direct into the 

 Atlantic, cut to about the same depth. This proves that they all had reached 

 a definite base-level, below which they could not cut, and this base apparently 

 must be the lowest sea-level of post-glacial times. For this reason my map 

 shows no connection with the Continent, except near the Straits of Dover and 

 across the southern half of the North Sea. 



The Irish peat-bog mammals referred to by Dr. Scharff are all good swim- 

 mers, even the pig, and could quite well have crossed a narrow strait. The 

 hy;ena of the caves belongs to an older period than that under discussion. 



