252 BRITISH PLANTS 



2. Callima-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 Ulex europceus 

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

 ovina, Air a 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 confined to Cornwall, the former almost so, and 

 Dabcecia 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 Calluna-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. 



