2o8 The Irish Nahiraiist. December, 



so that the serpentine soil has nothing to do with its present 

 distribution. 



Chance introductions of seeds during thousands of years 

 explain the existing peculiarities of geographical distribution 

 in a way that no changes of sea or land or climate will do. 

 Our alpine flora consists largely of survivors from a colder 

 period ; the rest of our llora, on the other hand, is constantly 

 being added to by chance introductions from the nearest 

 continental shore. That is why the Atlantic element, and 

 the eastern element, though not consisting to any great 

 extent of maritime plants, are conhned mainly in Britain to 

 areas within a few miles of the coast. Seeds are evidently 

 brought from the Continent and scattered broadcast over 

 certain coastal districts, and they grow and spread where soil 

 and climate are suitable. But the post-Glacial period has 

 been so short that the process is still incomplete, and tlie 

 slow spreading inland has only as yet extended a few miles. 

 We can still lix the point or points of introduction. 



The most striking elements in the British flora, except the 

 arctic and alpine species, have a marked coastal distribution. 

 The plants found correspond with those of the land opposite 

 (in which they are often inland, as well as coastal). Thus the 

 Cornish plants and those of S.W. Ireland contain a large 

 Pyrenean element ; Norfolk plants correspond with those 

 of the opposite shore of the North Sea ; even two or three 

 American plants are found on the coasts facing America. 



All the evidence seems, therefore, to point to a steady 

 change and increase in our flora, due to occasional intro- 

 ductions. These introductions are, I think, now mainly due 

 to birds driven by exceptional gales. But herds of migrating 

 bison, deer, and horse have played their part, especially 

 when the Straits of Dover were much narrower or non- 

 existent. Packs of wolves which hunted the large game, 

 foxes, cats, and especially raptorial birds which waited for 

 and struck down the tired migrants, must also have assisted. 

 Fences and the destruction of wild animals have j)robably 

 rendered the process far slower than formerly ; hut it still 

 goes on, as anyone can see who notes the constant occurrence 

 of seedling oaks miles from the nearest tree. 



