134 HEV. G. HENSLOW — ORIGIN AND DISTRIBUTION 



mostly or entirely absent from the warmer lowlands which separate 

 such widely-severed districts. 



If, however, we now leave Europe, and endeavour to find any 

 British plants elsewhere, we shall discover small groups of this last 

 type appearing here and there in many parts of the world. The 

 following numbers will indicate how many British plants have been 

 hitherto found in the several localities, and will also illustrate 

 the fact that the plants of Britain, like Her Majesty's dominions and 

 subjects, arc world-wide in their dispersion. Travelling eastwards 

 from the Ural Mountains, Siberia contains about 750 British plants, 

 and within the area included between the Kiver Obi and Behring's 

 Straits, and bounded southwards by the Arctic Circle (lat. 66|-°), 

 there are 111. Kamskatka contains 140. In North-east Asia, 

 including the area from Behring's Straits to South Japan, there 

 are 325, of which Japan has 156 British species. 



Next, regarding the extension of our plants eastwards along 

 the southern line of mountains, Hooker and Thomson give a 

 list of 222 British plants which reach India.* These appear 

 to have travelled eastwards from Europe, finding means of 

 transit along the Taurus, Caucasus, and western hilly or moun- 

 tainous regions; and the above authors remark that "the key- 

 stone to the whole system of distribution in Western Asia does 

 not rest so much upon a number of ' representative ' species as upon 

 the fact that not only are a large proportion of annual and 

 herbaceous species of each common to Western India and Europe, 

 but of shrubs and trees also. Those of North Europe inhabit the 

 loftier levels of the Himalayas, where they blend with the 

 Siberian types." The following British trees and shrubs occur in 

 India: — Berleris vulgaris, Prunus Padus, P. Avium, Ruhus fruti- 

 cosus, R. saxatilis, CratcBgus Oxyacantha, CotoneasUr vulgaris, Pyrus 

 Aria, Rihes Grossularia, R. nigrum, Hedera Helix, Buxus semper- 

 virens, JJlmus campestris, Salix ptirpurea, S. alba, Taxus haccata, 

 and Jxmiperus communis. It may be added that European types 

 disappear eastwards gradually at first, but rapidly after reaching 

 Kumaon. Few species enter Nepal, and still fewer reach Sikkhim. 

 Of the plants which cross the Indian mountains and appear in 

 Tropical Asia {i.e. India south of the Himalayas, the Khasia 

 mountains of Eastern Bengal, together with the mountains of both 

 peninsulas of India, Ceylon, and Java), the number, as might be 

 expected, is much reduced, only 23 species being found there. 



The next distributions to be considered are along the three 

 greatest lines of extension of land into the southern hemisphere — 

 namely, first, from India, through the East India Islands to 

 Australia, Tasmania, New Zealand, and the islands to the south ; 

 secondly, from Europe, through Africa and the islands near the 

 coast to the Cape ; thirdly, from Greenland and arctic America to 

 Cape Horn ; lastly, the isolated spots in Polynesia, which can boast 

 of a few representatives of the British flora. 



* 'Flora Indica,' p. 109 (1855). 



