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 Ulex europeus 
is most abundant. Grasses are common—e.g., Festuca 
ovina, Aira flecuosa, 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 H. vagans, 
the latter confined to Cornwall, the former almost so, and 
Dabecia 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 FHrica 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. 
