322 SOIL TYPES [chap. 



Pinus pinaster, are particularly intolerant of calcium 

 carbonate. 



Many of the Ericaceae, such as common heather and 

 the heaths, cultivated species like the rhododendrons 

 and azaleas of our gardens, are similarly intolerant of 

 lime and associated with sandy soils ; at higher levels 

 various species of Vaccinium and kindred plants are 

 common. Gorse (Ulex europceus and U. nanus), broom 

 (Cytisus scoparius), Genista anglica, Ornithopus, and 

 several vetches like Vicia cracca, are characteristic legu- 

 minous plants of sandy soils. The foxglove {Digitalis 

 purpurea), sorrel {Rumex acetosella), and in undraincd 

 situations the sundews (Drosera sp.) are intolerant of 

 lime and are common plants on sandy soils, as also 

 are the common bracken (Pteris aquilina), and wavy hair 

 grass (Aira flexuosa). 



Characteristic weeds of sandy soils are, spurrey 

 {Spergula arvensis) and sandwort-spurrey (Spergularia 

 rubra), corn marigold (Chrysanthemum segetum) and 

 knawel (Scleranthus annuus and perennis) ; Papaver 

 dubium and Centaurea cyanus are also common on 

 such soils. The bulbous buttercup {Ranunculus bul- 

 bosus) is very frequent on dry pastures, whether sandy 

 or chalky, as is the small bindweed {Convolvulus 

 arvensis) of similar soils under cultivation ; the silver- 

 weed (Potentilla anserind), though generally indicative 

 of winter flooding, is to be found on all kinds of poor, 

 light land. 



The Loams. 

 The sandy soils pass by imperceptible stages into 

 the loams free-working soils containing enough^ sand 

 to be friable and to admit of percolation, yet retain- 

 ing sufficient water near the surface to withstand 

 short spells of dry weather. If the sandy fractions of 

 the loam are mainly fine grained, the soil is apt to 



