Heath Association on Hindhead Common. 153 
occasional specimen of Pinns or Betula or one of the isolated 
patches of Ulex europceus above referred to. This vegetation is 
however not nearly as pure as it appears at first sight, for not only 
is the ground very largely occupied by the procumbent form of 
Ulex minor, but scattered plants of Erica cinerea, E. Tetralix and 
Vaccinium Myrtillus are to be found over the whole surface. Except 
for the Calluna and Ulex minor however no other form can be 
regarded as dominant (C U facies, cf. map). The growth of the 
ling on this part of the heath is very dense, for the plants, although 
their bases are quite widely separated from one another, branch 
very profusely above, so that the upper branches of adjacent plants 
are generally close together. A striking feature is the very uniform 
level of the top of this Calluna-zone. This appears to be due to 
the fact that projecting tips, which grow beyond the level of the 
surrounding growth, tend to dry up and die away—a fact, which 
may be in part responsible for the very profuse branching exhibited 
by the plant in its upper portion. It is probable that the vertical 
growth of this tall Calluna takes place very slowly, although we 
have no satisfactory data as yet on this point. 
Except where Ulex minor covers the ground there is thus 
plenty of room for the growth of other plants, but this growth has 
to take place under the shade of the Calluna, and the conditions 
are evidently not favourable. 1 Erica and Vaccinium are chiefly 
found where there is a break in the general continuity of the Calluna- 
level, whilst where the latter grows densely, the ground often bears 
no growth except for Mosses (Polytrichum juniperinum, more rarely 
Leucobryum) or Lichens (chiefly species of Cladonia). Bracken is 
altogether wanting over considerable areas of the ridge-top, and, 
when present, is represented only by isolated plants or small patches, 
the fronds of which rise to only about half the height of those in 
the valley. It is probable that the ridge-vegetation illustrates the 
oldest phase of the heath on the area under discussion (cf. below, 
p. 161). 
This Calluna-Ulex vegetation extends downwards for a varying 
distance on to the slopes of the central ridge, but is terminated by 
a sharp limit (no doubt representing the line of termination of a 
heath-fire), visible even from afar (cf. PI. V, fig. 1). In the lower 
half of the area concerned the C U facies extends down at some 
points to near the bottom of the valleys, actually reaching the path 
in valley A for a stretch of about 200 feet. A small distinct patch 
1 cf. Tansley, loc. cit., p. 104. 
