148 VEGETATION OF THE PEAK DISTRICT [CH. 



that there is some flow or trickle of water, i.e., the water is well 

 aerated. 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 /. sylvaticus 

 (= J. acutiff,orus), of J. lamprocarpus, of J. supinus, and of 

 J. squarrosus on the sandstones, shales, or peat ; of J. glaucu^ 

 on the limestones chiefly ; and of /. bufonius on almost any soil. 

 In certain lowland localities, associations of J. subnodulosus 

 (= /. obtusifiorus) occur, and, in maritime localities, of J. mari- 

 timus, locally of J. acutus, and of /. 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 effususwould 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 b). 



1 An abbreviation of Juncetum Junci-effusi. 



