GRASSLAND ASSOCIATIONS 259 



small or narrow, so that the plants approach very closely 

 to the rosette-plants in habit e.g., Scabiosa Succisa 

 (devil's-bit scabious), Campanula rotundifolia (hairbell), 

 and* Pimpinella Saxifraga (small burnet-saxifrage). The 

 most abundant creeping plants are : Trifolium repens 

 (Dutch clover), T. dubium (small yellow trefoil), Lotus 

 corniculatus (bird's-foot trefoil), Galium saxatile, (heath- 

 bedstraw), G. verum (lady's-bedstraw), and TJiymus 

 Serpyllum (wild thyme). Where the soil is calcareous, 

 lime-loving plants are common e.g., Linum catJiarticum , 

 Poly gala vulgaris (milk wort), Viola hirta (hairy dog- 

 violet), and Helianthemum Chamcecistus (rock-rose). On 

 dry soils heath-plants may be abundant e.g., Ulex 

 europceus (gorse, furze) and Pteris aquilina (bracken), 

 together with scattered dwarfed plants of V actinium 

 Myrtillus (whortleberry) and Calluna vulgaris (heather, 

 ling). When these plants are abundant, the natural 

 pasture passes over into a grass-heath. 



Alpine Pasture. At an altitude of about 2,000 feet 

 and over, a natural pasture may occur on rich soils. 

 The dominant grasses are those found at lower levels, 

 but Nardus stricta is more abundant, and may share 

 dominance with the others, and the viviparous variety 

 of Festuca ovina is common. But, above all, the alpine 

 pasture is distinguished by the presence of alpine plants, 

 of which Alchemilla alpina (alpine lady's-mantle) is a 

 constant and abundant representative. Most of the 

 herbs occurring at lower levels are found here, and, in 

 addition, the following alpines : Poa alpina, Potentilla 

 Crantzii (alpestris, alpine cinquefoil), Cerastium alpinum 

 (alpine mouse-ear chickweed), Lycopodium Selago, L. 

 alpina, L. davatum (club-mosses), and confined to Scot- 

 land or North Britain Sagina Linnwi (mountain- 

 spurrey), Oxytropis uralensis, Gentiana nivalis, and 

 Kobresia caricina. 



Limestone-Pasture and Chalk-Downs. The soil formed 

 on a hill composed of limestone or chalk is invariably 

 dry, for the rock allows the water to drain away very 

 rapidly the chalk to a much greater extent than the 

 limestone. The rock itself is very soluble in water con- 

 taining carbonic acid gas, and the soil-water consequently 

 contains a large percentage of bicarbonate of lime. 

 .Many plants prefer a dry soil, and others a chalky one 



