132 Plant-formation of Siliceous Soils 



has probably never been tree-clad — at least, not in post- 

 Tertiary times. 



A certain amount of grazing of sheep and cattle takes 

 place on these uncultivated hill-slopes, but the amount is, 

 on the whole, rather small. The land is not artificially 

 manured or drained. 



Two types of siliceous grassland have been described^ 

 as occurring on the Pennines, and have been distinguished 

 as wet and dry. The most abundant and characteristic 

 grass of the drier siliceous grassland is the mat-grass 

 {Nardus stricta) and that of the wetter siliceous grassland 

 is the purple moor-grass (Molinia cserulea). The former 

 may be termed Nardus grassland and the latter Molinia 

 grassland. The two species are respectively dominant in 

 the two associations, since they nearly monopolise the 

 ground and form the great bulk of the turf in which the 

 other plants are rooted; and the associated species are 

 therefore more or less controlled by the dominant plants. 

 To a limited extent, the associations are layered plant- 

 communities; and the smaller plants receive a certain 

 amount of shade and shelter from the dominant ones. As 

 is usual in plant-associations, one or other of the dependent 

 species occasionally becomes social; and thus plant- 

 societies arise. 



(i) Nardetum strict^. The typical JSTardetum of the 

 Pennines occurs on steep shaley slopes. In summer, this 

 association is characterised by a grassy turf, grey-green 

 in colour, dry and slippery. In late autumn, winter and 

 early spring, the ground is damp and sodden; and the 

 bleached haulms of the mat-grass (Nardus stricta) give 

 tone to the landscape, and may be recognised at a con- 

 siderable distance. The silver hair-grass (Deschampsia 

 flexuosa) is, on the southern Pennines, a constant associate ; 



^ Smith and Moss (1903) ; Smith and Eankin (1903) ; Lewis (1904, 

 a and 6). 



