BRITISH PLANT ASSOCIATIONS. 299 



not possible to distinguish between them. The vast 

 majority of British plants, or at least of those that are to 

 be considered as really wild, belong to the Oak or 

 Beech floras. 



5. The Mediterranean or Portuguese Invasion. The 

 Cornish Heath and others are found in a few isolated 

 spots along the South and South-west of England, and 

 nowhere else. Most of their habitats are in the little 

 strip of England which enjoys from 1600-1700 hours 

 of sunshine annually. See Bartholomew's Physical 

 Atlas, Plate 18 (H. N. Dickson). 



The arrangement of these successive belts seems to 

 show that, after the removal of the ice sheet, the 

 island was colonised from the South and South-west 

 by successive companies of immigrants. It is possible, 

 however, that the above account is too general, and 

 that many may have entered the country from the 

 East, across what is now the German Ocean. 



One small body of American-Irish plants, the Blue- 

 eyed Grass (^Sisyrinchiuni) and Eriostemon sexangulare, 

 seems to have travelled across the Atlantic. But though 

 there may be many exceptions, the only broad general- 

 isation possible appears to be, that the main body of our 

 British Pine, Oak, and Beech floras came from the 

 South and South-west, and then gradually overspread 

 the islands from South to North. 



The above description does not apply to the fol- 

 lowing groups (7), the Water and Marsh flora (see Chap. 

 IX.), (8) the Seaside flora (pp. 191 to 197), and (9) 

 Weeds and Introductions. The last is a large and 

 heterogeneous body, coming from almost every part 

 of the globe, and still in course of immigration. A 

 very short notice of these will be found in the con- 

 cluding chapter. 



