,4 
Somerset Heath and its Bryophytic Zonation. 
9 1 
VII. Zone of Hypuuin cupressiforme v. ericetorum. In the 
driest portions of the tussocks bryophytes are scarce, the only one 
which occurs with any frequency being H. cupressiforme and its 
variety ericetorum. Molinia coerulea is the dominant vascular plant 
but many invaders occur and are often “ drawn ” owing to the shade 
of the Molina and the overspreading Myrica. A definite species of 
Rubus with long trailing stolons is frequently present. 
The following list shows the chief plants found in this zone :— 
Polygala serpyllacea f 
Hypericum humifusum o 
„ pulchrum o 
Linum catharticum o 
Potentilla erecta a 
Rubus sp. f 
Ulex gallii a 
Galium saxatile o 
Scabiosa succisa f 
Senecio sylvaticus o 
Leontodon bispidum f 
„ nudicaule o 
Galeopsis tetrahit f 
Juncus squarrosus o 
Luzula multiflora f 
,, var. congesta f 
Agrostis tenuis f 
Holcus lanatus f 
Molinia coerulea d 
Blechnum spicant o 
Lastrea aristata o 
„ spinulosa o 
Hypnum cupressiforme o 
,, var. ericetorum f 
Thuidium tamariscinum o 
Laccaria laccata o 
III. Formation and Probable History of the Heath. 
The heath is doubtless the surviving remnant of a much more 
extensive one and may be considered to represent a stage—exhibiting 
a number of successional phases—between a wet undrained peat¬ 
moss (Sphagnetum) and a dry heath. This view is substantiated 
by the marginal associations and the local history. The evidence 
scarcely indicates a degenerate forest though the alder thicket was 
probably more extensive and birches ( Betula pubescens) more 
abundant. An oak-birch wood, in which Sphagnum is frequent, is 
present in the district, but does not immediately adjoin the heath. 
A road, which is known as the Drift, runs alongside the heath and 
this is locally supposed to have been cut as a drain. This supposi¬ 
tion may be correct as the road, though very straight in comparison 
with the tortuous lanes usually found in country districts, cannot be 
definitely attributed to the Romans. 
The two main factors determining the succession are (1) 
increased drainage leading to decreased moisture of the soil and 
(2) increased accumulation of humus on the hummocks isolated by 
by the drainage channels. At least five stages of succession may 
be distinguished in its present vegetation. 
(1) Sphagnetum recurv'd. Every portion of the heath has 
been more or less affected by human agencies but the lower, flatter 
and swampy portion has the nearest approximation to the primitive 
