148 VEGETATION OF THE PEAK DISTRICT _ [cH. 
that there is some flow or trickle of water, 7.e., the water is well 
aérated. The swamp association of siliceous soils is typically 
dominated by the common rush (Juncus effusus), yet it is a 
different plant community from the Juncus facies of the sili- 
ceous grassland previously described (see page 108). In this 
district, the swamps of Juncus effusus are not of sufficient size 
to be given a special colour on the maps, although Pethybridge 
and Praeger (1905) were able to do this on their vegetation 
map of the district lying south of Dublin. 
The term “Juncetum” has been used by several writers to 
denote a plant association whose chief constituent is a species 
of the genus Juncus. Such terms were first used by the Danish 
plant geographer Schouw (1822); but the term “Juncetum ” is 
vague, as it does not indicate the species of Juncus which is the 
dominant plant. In this district, for example, there are several 
kinds of “Junceta.’ The associations at the stream sources 
have usually Juncus effusus as the chief constituent plant ; 
but, besides this, associations or societies occur of J. sylvaticus 
(=J. acutiflorus), of J. lamprocarpus, of J. supinus, and of 
J. squarrosus on the sandstones, shales, or peat; of J. glaucus 
on the limestones chiefly; and of J. bufonius on almost any soil. 
In certain lowland localities, associations of J. subnodulosus 
(=J. obtusiflorus) occur, and, in maritime localities, of J. mari- 
timus, locally of J. acutus, and of J. Gerardi. Thus the term 
“ Juncetum” is very vague and ambiguous. To overcome the 
ambiguity, Cajander (1903) has adopted a modification of 
Schouw’s plan. Cajander would add the specific name as a 
genitive to the term “Juncetum”: thus, an association of 
Juncus effusus would be denoted by the term “Juncetum effusi}.” 
This plan is capable of universal application with regard to 
pure associations; and hence is of great merit. Of course, 
such universal terms will not supersede the common or ver- 
nacular names of plant associations, just as Bellis perennis is 
still known as the daisy and just as trichlormethane is still 
known as chloroform. However, many associations are destitute 
of common names; and, in any case, the technical names possess 
all the advantages of the binomial names in general use among 
botanists and zoologists, and of the technical names in use 
among organic chemists (cf. Moss, 1910 d). 
1 An abbreviation of Juncetum Junci-effusi. 
