071 the Origin and Distrihutluyi of the British Flora. 75 



followed by one of great depression, reducing Great Britain 

 to an archipelago, in which only alpine plants would survive. 

 Then followed a second continental period, readmitting the 

 flora of Europe to the British Isles, but so rapidly succeeded 

 by depression to present levels that, reckoning the flowering 

 plants and ferns of Great Britain at l'J:25, only 970 had time 

 to reach Ireland.^^ 



As we travel eastwards from the Mediterranean, through 

 the Levant, Caucasus, Persia, the Himalayas, China, and 

 Japan, we find the traces of the retreating American Miocene 

 flora more and more numerously. The fan-palm, the plane- 

 tree, and the walnut of the East, and the magnolias of the 

 Himalayas, China, and Japan, have the meaning of their 

 distribution still more strongly brought out by the discovery 

 of a tulip-tree in Central Cliina.^^ 



Mr. Bentham points out^* that the northern flora has 

 undergone a specialisation into three secondary floras, the 

 Arctic-Alpine, theTemperate, aiid the Mediterraneo- Caucasian. 

 The first of these, common in some degree to the Old and 

 New World, has been driven into every latitude, surviving on 

 the mountains when glacial gave way to warm conditions, 

 often on their southern slopes. The Temperate flora consists 

 largely of genera common to every longitude, easterly exten- 

 sions of American groups, such as the deciduous trees ; 

 whilst the Mediterraneo-Caucasian, comprising six-sevenths 

 of the species of Europe, and bounded by the deserts of 

 Africa and Arabia, but having outliers on the mountains of 

 Tropical Africa, may represent the remnant of the flora of 

 Europe previous to the Arctic-Alpine and American Miocene 

 invasions. 



Whilst we are not concerned with the Tropical flora, that 

 of the disconnected lands of the Bouth has an important 

 bearing on our present subject. In the West of Europe is a 



22 Hewett Watson, cited by Mr. Wallace, op. cit., id. 320. 



23 Moore, ' Journal of Botany,' 1875, p. 225 ; Oliver, ' Natural History 

 Eeview,' 1862; and W. T. T. Dyer, article "Distribution," Eneyclop. 

 Britan., 9th ed., vol. vii. (1877), p. 287. 



2^ Op. cit., summarised by Dyer, op. cit. 



