MOORLAND AND ALPINE PLANTS 395 



3 and 4). In the Crowberry (Fig. 253, 1) the hairy edges 

 meet, while the Ling has the smallest leaf, and its under 

 surface is confined to a narrow groove. In all these cases 

 the stomata occur only on the under surface. 



The Bilberry (Fig. 254, 1) usually sheds its leaves in the 

 autumn, but its bright-green angular stems (Fig. 254, a, b, c) 

 render it functionally evergreen. Small stunted forms, 

 however, of the Bilberry retain their leaves through the 

 winter. The Bilberry is able to withstand great extremes ; 

 it ascends to a greater altitude than the other species, and 

 is frequently the dominant plant on high, exposed, rocky 

 summits. 



Moorland grasses have also rolled leaves (Fig. 255). 

 Along their upper surfaces are ridges, between which are 

 lines of large, water-containing cells. When water is 

 abundant and these cells are distended, the blade spreads 

 out ; but in times of drought, water is withdrawn from the 

 cells, the ridges in consequence fall together, and so the blade 

 rolls up. In the grasses, therefore, the blades are up-rolled, 

 and not, as in the heaths, back-rolled. In the grasses, too, 

 the stomata are on the sides of the ridges on the upper 

 surface, and are absent from the lower more exposed sur- 

 face, which is protected by a thick cuticle. In either case 

 the rolled leaf encloses a chamber of still air, and as the 

 stomata are in this, they give off very little water. In 

 these ways plants are well adapted to withstand the severe 

 conditions of life on the moors. 



The water-logged, acid peat decomposes very slowly, and 

 the mineral substances it contains are not readily available 

 for plant-food. Peat-plants, however, agree in one respect 

 with those growing in humus : they are able to subsist by 

 the aid of mycorhiza, which is present on the roots of most 

 moorland plants. 



A plant often abundant on Heather moors and on moun- 

 tain slopes is the Gorse or Whin (Figs. 132 and 256), and 

 it exhibits many interesting modifications which should be 



