430 THE ECOLOGY OP PLANTS. 



corolla nearly globular (Fig. 179), calyx small, ovary inferior, fruit a 

 berry. Some other species of Vaccinium (Cowberry, Cranberry) occur 

 in Britain, but are local and rare ; they have evergreen leaves. 



The Crowberry (Empetrum nigrum) is an evergreen "ericoid 3 ' 

 (heather-like) plant with narrow rolled-up leaves, though not related 

 to the Ericaceae. It is rare in the south of England, but in the north, 

 especially on the Yorkshire moors, it is often the dominant plant over 

 large areas. Its leaves are in whorls of 3 and 4 and are rolled up so as 

 to enclose a rather large cavity, and the margins of the narrow slit are 

 covered with hairs, those on the two edges interlocking and thus mak- 

 ing the leaf an almost closed tube. The flowers are small, dioecious, 



axillary, sessile, and wind-pollinated, 

 with 3 sepals, 3 petals, male with 3 long 

 stamens, female with six spreading 

 stigmas on a short style ; fruit a black 

 globular drupe with a single stone. 



The Grasses found on moors and 

 heaths are mostly quite different from 

 those growing in meadows. In some 

 of the dry-heath grasses, e.g. Mat- 

 grass, Sheep's Fescue, and Wavy 

 Hair- grass, the leaves are rolled up 

 Pig. 179. Flower and Stamens of so that the upper surface forms the 

 Bilberry. inside of a narrow tube opening by a 



narrow slit. Purple Bent (Molinia), 



the typical grass of wet heaths, has narrow but flat stiff leaves ; on 

 high moors it is rarely over a foot high, but in lowland bogs it reaches 

 a height of 2 or 3 feet. 



When the same species of flowering plant or fern grows both in low- 

 lying or sheltered places and on bleak exposed hills or moors, there is 

 usually a marked difference in the height of the plant, the exposed 

 plants being stunted and having usually narrower and stiffer leaves 

 with thicker cuticle. This is well shown by the Bracken-fern. Two 

 species of Clubmoss (Lycopodium, allied to the ferns) grow commonly 

 on moors and heaths ; the Common Clubmoss (L. clavatum) has its 

 creeping stems densely clad with very small pointed leaves, and sends 

 up erect branches bearing less crowded leaves and ending in the " club " 

 or "cone" which bears the spore-cases (one in the axil of each cone- 

 leaf), while the Fir Clubmoss (L. selago) has no " club " but sends up 

 numerous erect branches with spreading leaves, the upper leaves having 

 spore-cases in their axils ; a third species (L. inundatum) grows in bogs 

 and has a more trailing habit and less erect branches than the two 

 species just mentioned. 



406. Bog-Plants. The typical bog occurs on heaths and 

 moors, associated with Heather and other heath-plants, and 

 its vegetation consists of peat-forming and peat- loving plants. 

 The distinctions between a marsh and a bog are fairly clear 

 in most cases, though there are transitions from one to the 



