394 



ECOLOGY 



becoming rusty brown in the autumn. The Heather moors 

 are a lighter green in summer, assuming a rich purple 

 towards autumn, when the plants are in flower. This is 

 a region of dwarf evergreen shrubs, the dominant species 

 being the Ling (Fig. 253, 2). 



The peat of the Heather moor is shallow, often sandy, 

 and acid, and is frequently developed over sandstones or 

 other areas with a shallow, well-drained siliceous soil ; but 

 Heather moors also occur, as we have seen, over limestone. 



At the base of the peat is often found a hard gritty layer 

 called the ' moor pan ', consisting of sand-grains bound 



Fig. 255. Sections of Up-rolled Leaves of Moorland Grasses 

 and Sedges. 1, Tufted Hair-grass; 2, Sheep's Fescue-grass ; 

 3, Mat-grass ; 4, Waved Hair-grass ; 5, Many-headed Cotton- 

 grass ; 6, Single-headed Cotton-grass ; a, air-spaces. 



together into a compact bed, a few inches in thickness, by 

 either oxide of iron or humus-compounds. This pan is 

 often so hard that roots of young trees cannot penetrate it. 

 The plants found on heaths have many features in com- 

 mon. The shrubs, with the exception of the Bilberry, are 

 all evergreen, with greatly reduced, back-rolled leaves, as 

 shown in Fig. 253. An interesting series comprises Cow- 

 berry (Fig. 254, 2) with edges slightly curled back, Cranberry 

 (Fig. 254, 3), and Cross-leaved and Fine-leaved Heaths 

 {Erica Tetralix and E. cinerea), farther back-rolled (Fig. 253, 



