CHAP, vii.] DISTRIBUTION OF PLANTS. 201 



ice-sheet did not pass south of the Thames valley, 

 consequently in the southernmost portions, the plants 

 already enumerated as remnants of the Pliocene age 

 managed to hold their own. During this period of 

 intense cold a new alpine flora was established in Wales 

 and Scotland, when the mountain summits of these coun- 

 tries were low islands, or members of chains of islands 

 that extended to Scandinavia through a glacial sea, and 

 a fair proportion of the Scotch Alpine flora arrived 

 during this period from the last-named area. 



At the period when the arctic rigour of the glacial 

 period gave way to the present conditions of climate, 

 the area now occupied by the German Ocean was dry 

 land ; in other words, England formed a western exten- 

 sion of the continent, and along this route the great 

 bulk of our lowland flora, as existing at the present day, 

 reached us from the Germanic region of the mainland. 



In a general view of the distribution of plants over 

 the surface of the globe as existing at the present day, it 

 is observable that there is far less adaptation to exist 

 under extreme climatic conditions amongst Cryptogams 

 than amongst Phanerogams. This is, to a great extent, 

 due to the fact that in Cryptogams the primordial 

 method of utilizing water as the agent for enabling the 

 antherozoid, or fertilizing body, to reach the oosphere 

 has been constantly adhered to in every group ; and 

 although Cryptogams can endure a greater amount of 

 cold than Phanerogams, being found in higher latitudes 

 and at greater elevations, on the other hand Phanerogams 

 are far more abundant in arid regions than Cryptogams. 



Marine vegetation, with very few exceptions, consists 



