252 BRITISH PLANTS 



2. Calluna-Heath. 



This association occurs in similar situations to the 

 grass-heath, but on poorer soil, covered with a deeper 

 layer of peat. The peat is composed of mosses charac- 

 teristic of dry soils — e.g., Polytrichum and Dicranum. 



Calluna vulgaris is almost exclusively dominant, with 

 occasional areas in which Erica cinerea or Vlex eurofceus 

 is most abundant. Grasses are common — e.g., Festuca 

 ovina, Aira flexuosa, and Agrostis vulgaris. This abun- 

 dance of grasses distinguishes the Calluna-heath from the 

 heather-moor. The remaining vegetation is that typical 

 of dry soils, and includes most of the grass-heath plants. 

 Rare plants found include Erica ciliaris and E. vagans, 

 the latter cftnfined to Cornwall, the former almost so, and 

 Daboecia polifolia (St. Dabeoc's-heath), found only in 

 Connemara (see p. 213). 



Although most common on siliceous soils, this associa- 

 tion is not confined to them, being found occasionally 

 on limestone — e.g., Mendip Hills and Peak District. In 

 such cases many plants of the limestone-pasture occur, in 

 addition to the ordinary forms. 



3. Heather-Moor. 



The heather-moor occurs where the peat is deeper 

 (4 to 5 feet) and wetter than that of the CaUuna-heath, 

 and is found chiefly on the more gentle slopes of moun- 

 tain-sides. The peat is made up almost entirely of 

 Sphagnum ; in fact, the heather-moor sometimes arises 

 on top of a Sphagnum-bog. In other cases it is formed 

 by the drainage of a cotton-grass moor. 



The dominant plant, as a rule, is Calluna vulgaris, but 

 in the wettest parts it is displaced by Erica Tetralix. 

 The heather grows more luxuriantly here than on the 

 Calluna-heath, and sometimes reaches a height of several 

 feet. The thick dense growth forms excellent covert, 

 and most of the " shooting moors " belong to this asso- 

 ciation. The associates of the heather are the same 

 as on the Calluna-heath, but they are much less abundant. 

 Erica cinerea, however, is usually very common, and 

 moisture-loving plants are frequent. 



