Vl] MARSH AND AQUATIC ASSOCIATIONS 147 



heather association or in the cotton-grass association : in the 

 latter case, they occur in associations either of siliceous grass- 

 land, scrub, oak or birch wood. In all cases, however, the 

 source is marked by a swamp ; and these swamps are frequently, 

 but by no means invariably, dominated by the common rush 

 {Juncus effusus). 



As might be inferred fi-om the diverse surroundings of 

 these springs, there is a certain amount of diversity in their 

 flora. This difference, however, is less than might have been 

 anticipated, as the springs are all characterized by some trickle 

 of water implying a fair degree of aeration, and all are character- 

 ized by a low mineral-content, as is sufficiently indicated in the 

 analyses just given. 



The poorest flora is found in the swamps surrounding the 

 springs which occur on the peat moors. It is sometimes stated 

 that the larger rushes do not occur on peat ; but Pethybridge 

 and Praeger (1905 : 171) find an association Juncus effusus on 

 peaty soils, and this is also the case on the Pennines ; so that 

 the statement is too sweeping. It is true that Juncus effusus 

 is not a normal member of any of the plant associations on 

 peat with stagnant water; but whenever water from a spring 

 oozes through the peaty soil, there a community of the common 

 rush frequently occurs. The springs change their positions 

 from time to time, as may be seen by comparing the present 

 springs with those marked on the old " six-inch " Ordnance 

 maps. Probably when the peat was being originally formed, 

 the land round the then springs would be destitute of peat; 

 but when a spring at some later time issued from a different 

 place, two local changes in the vegetation would be called into 

 being. First, the swamp plants of the original spring would, 

 after a time, die ; and their places would be filled by plants 

 from the neighbouring moorland association, and peat would 

 thus form on the site of the old spring; and secondly the 

 aerated waters of the new spring trickling through the peat 

 at a different place would result in the death of many of the 

 moorland species of that place, and in the invasion of some 

 swamp-inhabiting species. 



On the non-peaty slopes and at lower altitudes, the swamps 

 are more numerous and much richer in species. However, the 

 characteristic feature of all of them, whether on peat or not, is 



10—2 



