The Southern Element in the Britisli Flora. 525 



closely to the widely distributed H. qitadrangidum that it is treated by them 

 as a western variety of it. Trichomanes radicans occurs in the warm 

 regions of both hemispheres and is evidently a relict of very great age. 

 Like the remaining species of the group it fits very naturally into the as- 

 semblage of Atlantic plants in the British Isles, Apart from the so called 

 North American species these last four species (5'a;r^/ra^a Qeiirn^ S. urn- 

 b7^osa, Pingiiicula grandiflora and Erica Mackaii are usually 

 quoted as the most puzzling instances of distribution among the British plants, 

 and they have attracted the more attention as they are^ within the British 

 Isles, confined to the extreme southwest and west of Ireland, The day 

 when Simethis planifolia disappears from its Dorset station will add 

 another species to the peculiar Irish element of the British flora. Then 

 we shall have the following progressive series of gaps between the Irish 

 and the continental areas of that element. 



Simethis planifolia^ S. W. Kerry — Eure 



Arbutus Vnedo, Kerry and Cork — G6tes du Nord 



Dahoecia polifoliaj Galway and Mayo — Maine et Loire 



Erica mediterranean Galway and Mayo — Gironde 



fraga Geum. 



S. iimhrosa 



Pinmi/ip/nln 



fi 



West and South- 



west of Ireland — Eastern Pyrenees 



Erica Mackaii Galway — Asturias. 



If on the other hand Simethis should disappear first in Ireland its 

 distribution in w^estern Europe would become a parallel case to that of 

 Erica vagans or E. ciliaris. Thus the apparent anomalies in the distri- 

 bution of those often quoted plants resolve themselves into cases of far 

 gone disintegration of area. How it has come about, or how the Atlantic 

 and Mediterranean elements of the British flora have arrived in their island 

 '^ome, is a question which cannot be dealt with here. This southern 

 element is like a weft in a woven fabric. It has not come alone. It is 

 associated here in these islands with species which we call > Central-Euro- 

 pean* or ^Germanic« although they are also found in the Pyrenees and 

 the mountains of Northern Spain. At whatever period this element may 

 have come into Great Britain and Ireland we must not think of its con- 

 stituents as wandering singly and independently of each other. 



Literature. 



(<) Gl. Reii) in Report Brit. Ass. Portsmouth, mi, pp. 573—577. 



(2) 0. Staff ibid. p. 578. 



(3) R. F. ScHARFF in The Irish Naturalist, 1912, pp. 105— m. 



(4) A. Engleh, Versuch einer Entwicklun^-sgeschichte der Pilanzenwelt, vol. I. pp. 



176 — 182. 



(i>) T. G. BoNNEY, Presidential Address in Report Brit. Ass. Sheffield, 1910, pp. 3 --34. 

 (6) E. FoHBEs in Mem. Geol. Survey of Great Britain, vol. T. pp. 336—342. 







