7] 



TYPES AND AREAS OF NATURAL DISTRIBUTIONS 



197 



western Ireland and only reappear, at least so far as natural occur- 

 rence is concerned, in some such distant region as the Iberian 

 Peninsula, an example being afforded by Mackay's Heath {Erica 



Fig. 61. — Map showing 

 ' Lusitanian ' distribution 

 of Mackay's Heath (Erica 

 viackaiana.) 



Fig. 60. — Map showing intracontinental discontinuous dis- 

 tribution in Australia of the section Erythrorhiza of the 

 genus Drosera (Sundews). (After Diels.) 



mackaiana), see Fig. 61. It has been suggested that the northern 

 stations in such instances may be relics of a postglacial warm period 

 or, in the case of some still more widely disrupted ranges involving 

 the tropics, of the interglacial ' pluvials '. 



Relic Areas 



These, as supposedly in the cases just mentioned, are areas 

 occupied by relic species (often called ' relicts ') which in the 

 phytogeographical sense are remnants of an earlier flora that have 

 been ' left behind ' when surrounding areas have been vacated. 

 Thus relic areas themselves normally constitute remnants of once- 

 extensive areas, being usually isolated and often contracting. 



The determination of whether a species is really a relic is not 

 always an easy and definitive matter, and the same consequently 

 applies to relic areas. Even when the usual criteria are applied we 

 may go astray, as in the case of some of the plants whose apparently 

 disrupted ranges were formerly supposed to indicate that they had 

 persisted on unglaciated ' nunataks ' through the Pleistocene glacia- 

 tions; yet when intermediate areas were properly explored the 



