PART V 

 ECOLOGY 



CHAPTER XXV 

 PLANT HABITATS AND COMMUNITIES 



Vegetation of the valley and mountain. In a walk from 

 the bottom of a valley to the top of a mountain many 

 striking changes in the vegetation are met with (Fig. 206). 

 Below is the river, with, perhaps, here and there, ponds or 

 lakes bordered with reeds, rushes, and other moisture- 

 loving plants, and trees such as Alders and Willows. The 

 flat ground beyond, composed of alluvium laid down in 

 the past by the river, is highly cultivated and occupied 

 by cornfields and meadows, bounded by hedgerows, with 

 occasional undrained patches of marsh. On the rising 

 ground these meadows gradually give place to pasture and 

 woodland or uncultivated heath ; stone walls often 

 replace the hedgerows ; and, as we ascend, the plants vary 

 in character according to soils, drainage, water-supply, 

 aspect, altitude, and the like. Higher still, the trees dis- 

 appear and give place to wild, bleak moorland, perhaps 

 covered with deep, wet, acid peat (Fig. 209) ; while the 

 rocky peaks forming the summits are covered with a vege- 

 tation very unlike that met with at lower levels. On such 

 high peaks the plants are exposed to great extremes of 

 climate, heat and cold, wet and drought, bright sunshine, 

 and dense, wet mist, driving and often drying winds, and 



