428 THE ECOLOGY OF PLANTS. 



The Bough Grass Moor or Grass Heath usually replaces 

 the Ling at the edges of the Heather Moor, and may be 

 divided into two types. One (Wet Grass Heath) is flat or 

 nearly so, wet, peaty, and dominated by the Purple Bent- grass 

 (Molinid), with the following among its associate plants : 

 Bog Violet, Blinks, Marsh Pennywort, Bell and Cross-leaved 

 Heaths, Bilberry, Bog Asphodel, Bushes, Sedges. The other 

 (Dry Grass Heath) occurs on the steep hill- sides, which are 

 well drained and therefore not peaty, and has plants adapted 

 to a dry habitat, the dominant plant being usually either 

 Sheep's Fescue-grass (Festuca ovina) or Mat-grass, with 

 Wavy Hair-grass and Bent-grass often abundant, and such 

 associate plants as Dwarf Gorse, Needle Whin, Heath Bed- 

 straw, Tormentil, Sorrel Dock, Milkwort, Bracken, etc. 



On low moors we find chiefly Ling, Heaths, Gorse, Bracken, 

 and low (usually creeping) plants which shelter under these, 

 e.g. Tormentil, Heath Bedstraw, Milkwort, Eed Rattle, and 

 in the boggy places various bog and marsh plants. One 

 naturally associates Ling and the Ericas with hills, but 

 extensive heaths are found, for example, along the coast only 

 a few feet above sea-level. Ling and the Ericas occur at all 

 elevations up to about 2000 feet ; above that height they are 

 often replaced by Bilberry. In the south of England, at any 

 rate, Bilberry often occurs extensively in dry woods ; altitude 

 in itself has little direct influence on the distribution of this 

 and of various other moorland plants, and one finds in 

 practice every transition from typical heather moors or heaths 

 to woodlands. 



Heaths may be very dry or very moist, often passing into 

 marshy land. Dry heaths overlie sand or chalk, from which 

 water drains rapidly; the average summer temperature is 

 usually low, the soil thin and poor in plant food, being often 

 only a few inches thick and forming the only reservoir from 

 which the plants draw their water in summer. 



4O5. Moorland and Heath Plants. Ling, Bell Heath, and 

 Cross-leaved Heath are closely allied plants, and are much -branched 

 wiry shrubs bearing crowded small narrow leaves. Each leaf is rolled 

 up so that the lower epidermis (bearing the stomates) forms the inside 

 of a tube which opens to the air only by a narrow slit (seen as a white 

 line along the underside), and the edges of the leaf bear hairs which 

 further hinder the escape of water-vapour. 



