626 Professor L. C. Mlall, [Feb. 18, 



then the heather bears few young leaves, while the fronds of the 

 bracken are only beginning to pnsh through the soil. Whatever the 

 weather, there is no protection against its extremes; there is no 

 shelter and no shade. The air is cold ; wind and the diminished 

 pressure due to height favour rapid evaporation. Though the Sphag- 

 num patches form permanent bogs, a great part of the moor becomes 

 far drier in a hot summer than auy pasture or meadow. The top of 

 the peat crumbles, and is blown about as dust, the loose sand can 

 hold no moisture, bared surfaces of clay become hard as iron. Another 

 feature which must profoundly atfect the vegetation of the moor is the 

 poverty of its water in dissolved salts. It is pure and soft, like dis- 



FiG. 4. — Transverse section of It af of Lino;, showino; large air- 

 spaces, the reduced lower epidermis which bears the stomates, 

 and the long hairs which help to close the cavity into which 

 the stomates open. 



tilled water, and contains hardly any mineral food for plants. The 

 plants of the moor are subject to the extremes of wet and dry, to cold 

 and to famine. 



The best known and most characteristic of the moorland plants 

 are the heaths. Ling, the common heather, is the most abundant of 

 all; it sometimes covers many square miles together, to the almost 

 complete exclusion of other plants. Ling is a low shrub, wliose wiry 

 stems creep and writhe on the surface of the ground. When sunk 

 in deep peat the stems are often pretty straight, but among rocks you 

 may follow the twisted branches for many yards, and at last discover 

 that what you took for small plants rooted near the surface are really 

 the tops of slender trees, whose roots lie far below. Bilberry, too, 

 wriggles among loose stones or fallen blocks till you grow weary of 

 following it. The leaves of ling are dry, hard and evergreen. They 

 last for two or three years, and do not fall ofi' as soon as they die, 



