August i8, 1898] 



NATURE 



379 



than any 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 affect the vegetation of the moor is the 

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

 distilled 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 



V 



Fig. 3. — Ling (Calluna vulgar 

 beneath, and a cro 



:afy 

 of 



section of the base of the leaf. 



abundant of all ; it sometimes covers many square miles together 

 to the almost complete exclusion of other plants. Ling is a 

 low shrub, whose 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 



Fig. 4.— Transverse section of le.-if of LinR, showing 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. 



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 off as soon as they die, but 

 crumble slowly away. They are very small, densely crowded, 

 and ranged on the branch in four regular rows. A good thin 

 section through a leaf is not easy to cut ; when you get one, you 

 tind that the interior is largely occupied by irregular air-spaces, 

 and that the stomates are sunk in a deep groove on the under 

 side of the leaf, where they are further sheltered by hairs. 



NO. 1503, VOL. 58] 



Ling is a plant of slow growth, and a stem which showed 

 seventeen annual rings was only a centimetre in diameter. Stems 

 of greater age than this are rare. After ten or twelve years the 

 plants flower scantily, and exhibit other signs of age. Then the 

 common practice is to burn them off. 



As we travel south, we find the ling getting smaller and smaller. 

 In Scotland it is often waist-deep, in Yorkshire knee-deep, on 

 Dartmoor only ankle-deep. On the moors of the south of 

 England the ling is generally much mixed up with grasses, as 



5.— Cross-leaved Heath {Erica tetralix), with part of a branch, 

 ilarged ; a leaf seen from the under side, and a section of a leaf. 



also on the verges of the Yorkshire moors. In Cornwall it may 

 grow so close to sea-level that it is wet with salt spray in every 

 storm, and its tufts are intermingled with sea-pink and sea- 

 plantain. At the Lizard, wherever the serpentine comes to the 

 surface, ling ceases, and the Cornish heath {Erica vagans) takes 

 its place. 



Here and there we find among the ling the large-flowered 

 heaths with nodding pink or purple bells (Scotch Heath, Cross- 

 leaved Heath). The leaves of these plants are much larger and 



Fig. 6. —Transverse section of rolled leaf of cross-leaved Heath {Erica 

 tetralix). 



thinner than those of ling; they are called "rolled leaves," 

 becau.se the edges curve downwards and inwards, partly con- 

 cealing the under surface, which bears the stomates. All our 

 native heaths agree in possessing wiry stems, long roots, and 

 narrow, evergreen leaves, with a glossy cuticle and small tran- 

 spiring surfaces. The tissues are very dry, and burn readily 

 even when green or drenched with rain. It is possible by good 

 management to set acres of heather in a blaze, even in mid- 

 winter, with a single lucifer match. The heaths wither very 

 slowly when gathered, and change little in withering. 



