The Sonthern Element in the British Flora. 







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By 



0. Stapf. 



At the meetinsr of the British Association for the Advancement of 



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Science at Portsmouth in 1911 a discussion took place on the relation of 

 the present plant population of the British Isles to the Glacial period. It 

 was opened by Mr. Clement Reid in an address in which he advocated 

 the theory that no temperate flora could have survived the conditions 

 f prevailing in the islands during the Glacial period, that the existing flora 



apart from a few arctic and alpine species, came in towards the end of, 

 and after, that period, and that especially the » Atlantic or Lusitanianc 

 plants (also referred to as »Pyrenean«) and the ^American* and »limestone« 

 elements arrived and, may be, still arrive by chance introductions of seeds, 

 now mainly due to birds driven by exceptional gales. I then expressed 

 my agreement with the speaker's view as to the effect of the glacialion 

 of the British Isles on the flora, and the reimmigration of the bulk of the 

 latter in post-glacial times, but combated the supposition of the presence 

 of the peculiar American, Atlantic and limestone elements being due to 

 chance introduction over great distances. Since then Dr. Scharff (3) has 

 thrown doubt on the theory of a wholesale destruction of the preglacial 

 flora of Great Britain and Ireland and refuted the idea of the introduction 

 of the »Pyrenean« element by migrating or gale-driven birds. In my 

 opmion the question of the presence of those peculiar elements and espe- 

 cially of the so called ^Atlantic*, »Pyrenean« or >Lusitanian« plants has 

 in a general way already been solved by Engler (4) in his >Versuch einer 

 Entwicklungsgeschichte der Pflanzenwelt* more than thirty years ago. To 

 him their immigration or rather reimmigration took place in post glacial 

 times — for he too assumes the wiping out of the greater part of the pre- 

 glacial flora during the Glacial period — and it happened along with the 

 repopulation of the eglaciated land by a flora advancing mainly from south- 

 western Europe through western France where the improvement of the 

 climatic conditions following on the retreat of the ice in the north set 

 in first. It might be sufficient to refer to the pages quoted from his book, 

 if it were not for the brevity with which he was obliged to deal with 

 the matter and for the fact that great confusion exists as regards the 



