PLANTS OF HEDGEROWS AND WALLS 337 



ing effects of the wind ; they lessen the rate of evaporation, 

 and in consequence help to maintain a higher temperature. 

 To render them more effective, spiny shrubs like the Haw- 

 thorn are generally selected, and large trees such as Oak, 

 Elm, Sycamore, Ash, and other forest trees are introduced 

 at intervals to provide shelter for the cattle. So numerous 

 are the trees that, when viewed from a distance, their 

 appearance is that of an open wood. Under the shrubs and 

 trees wild plants establish themselves, especially woodland 

 species, which are well suited to the shade of the hedgerow. 



Hedges are not of universal occurrence. They are 

 absent from the uncultivated, sandy wastes and salt-marshes 

 of our shores, and they are not found on our moorlands 

 and mountains. They accompany man in his farming 

 operations, but even here they have a peculiar distribution. 

 In areas over sandstones and limestones, where the soil 

 is shallow and the ground often stony, they are replaced 

 by stone walls. On the other hand, in wet, low-lying fen- 

 districts the ' fences ' commonly take the form of ditches 

 and drains. It is in better-drained areas and often over 

 deeper soils that hedgerows predominate. Hence their 

 geographical distribution is significant. Hedgerows are 

 also essentially English, and give a character to the land- 

 scape without parallel in any other country. 



Habitats of the hedgerow. In a common type of hedgerow 

 the shrubs and trees are planted on a bank, below which 

 is either a ditch or a moist hollow, and beyond this is a 

 grassy sward. Thus in a very limited area are the follow- 

 ing distinct habitats : (1) Under the shrubs, shade, pro- 

 tection, and a soil containing much humus. (2) On the 

 hedge bank, a well-drained, more exposed slope. (3) At 

 the bottom either a ditch filled with water or a wet hollow. 

 (4) A drier, flat, miniature meadow. In each situation 

 characteristic plants occur, showing many interesting bio- 

 logical features. Note how numerous are the plants with 



1296 V 



