26 



the moimtain summits of Britain were low islands, extending to 

 the area of Norway through a glacial sea, and clothed with an 

 arctic vegetation, which in the gradual upheaval of the land 

 and consequent change of climate, became limited to the summits 

 of the new-formed and still existing mountains." " 5thly. A 

 Germanic Flora, resulting from the upheaval of the bed of the 

 glacial sea and the consequent connexion of Ireland with 

 England, and of England with Germany, by great plains. This 

 Flora, which includes the great mass of our native plants, 

 extends over the greater part of Great Britain and Ireland, 

 mingling with the other Floras, and diminishing, though slightly, 

 as we proceed westward, indicating its easterly origin and 

 relation to the characteristic Flora of northern and western 

 Germany."* 



I have given the above theory for the most part in Professor 

 E. Forbes's OAvn words, and shall not stop to say more respecting 

 it. Having got our plants, let us proceed now to consider what 

 influences they will be subject to after their arrival, to favour or 

 retard their spreading as the case may be, some gradually taking 

 root everywhere, others settling doAvn in a given spot, or 

 appearing perhaps in more localities than one, with wider or 

 narrower intervals between these localities in which they are 

 not fciund These influences are mainly soil and climate, and 

 the relative advantages possessed by certain ^species over others 

 growing beside them. Some plants grow only on particular 

 rocks, or on alluvial soils formed in great measure by the 

 disintegration of such rocks ; others are less fastidious, and will 

 grow almost anywhere. Such is the character of many weeds 

 which obtrude themselves on our notice go Avhere we will. 

 Where there is the greatest variety of soils, there will be, 

 <:(ekris paribus, the greatest variety of plants ; where one character 

 of soil prevails chiefly, there may be a strong and luxuriant 



* Rep. Brit. Assoc, 1845. (Trans, of Sects.) p. 97. 



