24 THE WORLD OF LIFE CHAP. 



termed the British type ; that is, they are found in suitable 

 places over the whole of Great Britain, and in most districts 

 are so plentiful that they may be termed common plants 

 such are the Alder, Birch, and Hazel among trees and shrubs ; 

 the Honeysuckle, Ivy, Heather or Ling, Daisy, Chickweed, 

 Nettle, and a host of others. Another group is abundant 

 in England, but absent from the Highlands or from Scotland 

 generally, such as the Dwarf Gorse and Yellow Dead-Nettie. 

 Several arctic or alpine plants are peculiar to the Highlands, 

 a considerable number of species are found only in our 

 eastern counties, while as many or more are characteristic of 

 the west 



More curious perhaps than all these are the cases of 

 plants found only in one small area, or two or three isolated 

 patches ; and of others which are limited to a single station, 

 sometimes of a few acres or even a few yards in extent. 

 Such are the Cotoneaster, found only on Great Orme's Head 

 in N. Wales ; the Yellow Whitlow-Grass, on Worms Head 

 in S. Wales ; the pretty white-flowered Potentilla rupestres, 

 on a single mountain-top in Montgomeryshire ; the small 

 liliaceous plant, Simethus bicolor, in a single grove of pine 

 trees near Bournemouth, now probably exterminated by the 

 builder, and another plant of the same family, Lloydia 

 serotina, limited to a few spots in the Snowdon range ; the 

 beautiful alpine Gentiana verna, in upper Teesdale, Yorkshire, 

 and others confined to single mountains in the Highlands. 

 Between the extremes of widespread abundance and the 

 greatest rarity, every intermediate condition is found ; and 

 this is so far as we know, a characteristic of every part of 

 the world. This, again, affords a striking proof of that 

 struggle for existence which has already been referred to, 

 acting, as Darwin was the first to point out, first to limit the 

 range of a species, often so that it exists only in two more or 

 less isolated areas, then to diminish the number of individuals 

 in these areas, and finally to reduce them to a single group 

 which ultimately succumbs to an increased stress of competi- 

 tion or of adverse climatal changes, when a species which 

 may have once been flourishing and widespread altogether 

 ceases to exist. The rarity of a species may thus be 

 considered as an indication of approaching extinction. 



