34 HISTORY OF THE EUROPEAN FAUNA. 



the botanical aspect of the question, botanists are 

 quite in accord with the zoologists, and entirely 

 share their views in the belief of a former land- 

 continuity between the British Islands and the 

 Continent. " It cannot be denied," says Professor 

 Blytt (p. 32), "that a plant of one or another 

 species may, in an exceptional case, migrate, without 

 human assistance, all at once, across large tracts 

 of land and sea, and that such migration, if operating 

 during geological periods, might introduce a number 

 of species even into distant oceanic islands ; but 

 when the question is of whole communities of plants, 

 such as the above enumerated elements in our flora, 

 then such an accidental and sudden transport across 

 large tracts can only be conceived to be at all 

 probable in the case of Arctic plants carried by 

 drifting ice to a bare country without native flora ; 

 as to the other species, we must imagine that the 

 migration during the gradual change of climate has 

 proceeded sloivly and step by step across connected 

 tracts of cotmtty. In that manner we may assume 

 that our country has in the course of time obtained 

 its present covering of plants. Each of the above- 

 named elements in our flora has doubtless its 

 corresponding element in our fauna. The fauna 

 and flora of a region stand in relation of com- 

 plicated dependence to each other. The animals 

 live on the plants. The fecundation of the plants 

 takes place in a great degree by means of insects ; 

 their seeds are often scattered by resident birds and 



