200 INTRODUCTION TO PLANT GEOGRAPHY [CHAP. 



there is much fossil evidence that it was formerly widespread there 

 in the wild state. 



In general the main, non-relic part of an area either occupies its 

 original territory, any outlying parts having become separated owing 

 to habitat changes, or results from secondary dispersal, in which 

 case the relic part may actually lie within the main area. An example 

 of this latter type is afforded by the Scots Pine [Pinus sylvestris), 

 which has relic portions of its area in the mountains of Europe, 

 whereas its extensive occupation of surrounding sandy lowlands is 

 the result of secondary colonization. Such colonization may even 

 take place from a relic area, for example when climatic conditions, 

 whose deterioration in surrounding areas had led to isolation, 

 subsequently improve so that suitable plants can recolonize around 

 the isolated area. Much the same often occurs with the removal 

 of heavy grazing which had caused the restriction of some plants 

 to limited areas (that in a sense were then relic ones), whence they 

 spread again when the animals moved off or died. 



A species which occupies a relic area throughout its range may 

 be termed an ' absolute relic ', while one of which only an isolated 

 part of the area is relic is known as a ' local relic '. An 'endemic 

 relic ' is one that is restricted to a single region. Those relics which 

 achieve a secondary distribution by the occupation of suitable 

 habitats are known as 'migrant relics', the more recently occupied 

 habitats being termed ' pseudo-relic ' and the plants ' pseudo-relics ' 

 (or ' -relicts '), though these terms may also be applied in cases where 

 a plant acquires the apparent character of a relic without actually 

 being one. Most of these principles may be applied equally to 

 single species or other taxa, groups of species (as in relic colonies), 

 or entire floras. 



Many relics, having long been in partial disharmony with present- 

 day habitat conditions, have become depauperated in biotypes ; the 

 consequent loss of the capacity for variation and adaptation has led 

 to their being considered conservative. Such plants have often been 

 called ' senescent '. Being commonly restricted to narrowly specific 

 environmental conditions, they may fail to retain even their limited 

 area, in extreme cases becoming extinct. However, if favourable 

 conditions should reappear and, for example, allow the approach of 

 formerly segregated variants so that hybridization can take place and 

 new forms thereby arise, the species may take on its former vigour 

 or even exceed it and become aggressive. 



Leaving aside the so-called ' anthropogenic relics ' whose areas 



