A Somerset Heath and its Bryophytic Zonation. 85 
hryophytic one was present, though desmids were very abundant 
and characteristic. 1 Towards the edges of the stream other plants 
were found and it is purposed to take this as the more common 
facies of the second zone. 
II. The second zone is characterised by three alternating 
facies each dominated by a distinct species of bryophyte, and 
called here II A. 
The following plants are found in this second zone:— 
Potamogeton polygonifolius o Hydrocotyle vulgaris f 
Aneura pinguis a Pellia epiphylla a 
Hypnum scorpioides Id Sphagnum cymbifolium Id 
„ revolvens o „ „ v.squarrosulumo 
„ stellatum o „ recurvum la 
Aulacomnium palustre a „ rufescens o 
II A. Facies of Aneura pinguis and Pellia epiphylla. The 
first plants, apart from the algae, to relieve the isolation of the 
pondweed are the two thalloid anacrogynous Jungermanniales, 
Aneura pinguis and Pellia epiphylla. These are the dominant 
plants, not only at the margins of the zone of Potamogeton poly¬ 
gonifolius but also in the moist furrows where that may be absent. 
Both are variable, the thalli often becoming long and narrow, 
especially in Aneura pinguis which becomes very like Pellia in 
appearance (Pig. 6). Many of the Pellia plants are almost typical, 
but typical specimens of Aneura pinguis are seldom met with. 
This is correlated with the fact that the habitat is much nearer 
to the usual one for the Pellia than for the Aneura. Hydrocotyle 
vulgaris is occasionally present, but is more abundant in the 
swampy (lower) portion of the heath. 
II B. Facies of Hypnum scorpioides. In some places small 
shallow boggy pools are formed, and in these the Aneura and Pellia 
are usually absent, little vegetation of any kind occurring save the 
characteristically reddish Hypnum scorpioides, accompanied by a 
little H. revolvens and less frequently by H. stellatum. During dry 
weather these areas become patches of moist peat and H. stellatum 
then often shows a distinct secundity of its leaves. 
IIC. Facies of Sphagnum cymbifolium. In other cases these 
depressions form pockets of Sphagnum, especially S. cy>nbifoliu7n 
and its colour variety glaucescens. When a fair amount of shade 
is afforded by Myrica, etc., the pockets chiefly consist of S. cymbi- 
foliuin var. squarrosulum, which is characterised by having the 
leaves spreading out in a squarrose manner, thus compensating for 
1 Cf. G. S, West in Types of British Vegetation, p. 193. 
