194 



KNOWLEDGE. 



[Septembeb, 1908. 



are produced in early spring. The Ling (Calluna vulgaris) 

 is familiar to every one. It is tlie most abundant social 

 plant in the British flora. Over mile upon mile of moun- 

 tain and moor it dominates the vegetation, and is equally 



-Tl]c> .Str;i\vbeiTj--Tree on a Kcr 



lal;e-sh,.re. 

 [E. Wklih, Photo. 



at home on southern sand-dunes and on Scottish mountain- 

 tops. Examine the flower carefully. The calyx is con- 

 spicuous and coloured, deeply cleft into four lobes ; the 

 corolla quite insignificant in comparison, bell-shaped, and 

 much shorter than the calyx. Note also the tmy leaves, 

 arranged in four close rows. The genus Calluna possesses 

 only this one species ; but it makes up in number of 

 individuals what it lacks in variety. The Ling is spread 

 all round the Northern Hemisphere, and where it occurs it 

 usually forms a conspicuous feature of the vegetation. 



The Heaths proper (Erica) number six British species. 

 Two of these, the common purple Heather {E. cinerea) and 

 the pink Bell-Heather {E. Tetralix) are familiar plants on 

 every heath and mountain side. The other four are of 

 very local and peculiar distribution. Two of them, the 

 MediteiTanean Heath (E. mediterranea) and Mackay's 

 Heath {E. Mackaii) are confined to a definite area in the 

 west of Ireland, in the counties of Gal way and Mayo. The 

 other two, the Cornish Heath (E. varjans) and the Fringed 

 Heath (E. ciliaris), grow only in a restricted area in the 

 south-west of England, in Cornwall and Dorset. All 

 four are elsew^here found only in western France and the 

 Spanish peninsula. This group of four Heaths forms, 

 indeed, the focus of that peculiar group of plants of the 

 western edge of Europe — West Ireland, West England, 

 and the Pyrenean region — whose remarkable range has 

 given rise to so much speculation among naturalists, and 

 to the postulating of a former extension and continuity of 

 the edge of the Continent, which formed a land surface 

 along which these and other plants — and many animals 

 likewise— migrated freely on the old edge of the Atlantic 



(see Knowledge, December, 1901, pp. 284-6). Of the 

 four rare Heaths mentioned, I'L Mackaii is a small plant 

 with a habit like E. Tciralii- E. ciliaris is a taller hand- 

 some plant with bright flowers in unilateral racemes. E. 

 ragaiis grows several feet high, forming compact bushes 

 with stiff erect branches. The small flowers are borne in 

 racemes near the ends of the branches. E. mediterranea 

 is the largest British Heath, forming bushes which may 

 attain five feet in height, with erect branches clothed with 

 spreading leaves. The pink blossoms appear in early 

 spring, and the plant is usually at its best by March. The 

 remaining three genera. Azalea, PhyUodoce, and Daheocia, 

 each with a single species, are rare plants of restricted 

 distribution. Azalea proeombens is the most frequent of 

 the three — a tiny tuftetl shrub found on the summits of 

 high Scottish mountains, with crowded dark green leaves 

 and umbel-like clusters of pretty pink flowers. PhyUodoce 

 aernlea is also alpine in habitat, growing only on the Sow 

 of Athol in Perthshire. It is a low-creeping shrub, with 

 crowded narrow leaves and large single egg-shaped purjilish 

 flowers. Lastly we have Dabeocia polifoUa, the largest- 



FiG. 2. — St. Dabeoo's Heath. Half natural size. 



flowered of all the British Heaths, growing only in Galway 

 and Mayo, and forming another of the peculiar Irish- 

 Pyrenean plant-group which has been ali-eady referred to. 

 It is a trailing shrub, with ovate leaves conspicuously 

 white beneath. The stems end in racemes bearing beautiful 

 drooping egg-shaped bells half an inch in length. Its 

 abundance amid the bogs and mountains of Connemara 

 is to the botanist one of the most striking features of 

 that wild and fascinating country. 



Before passing away from the Heaths and their allies, a 

 word is desirable as to certain features of leaf and flower 

 which they display. In the flowers, the stamens strike us 

 at once as peculiar. Take the flower of the Bell- Heather 

 (E. Tetralix) for example (Fig. 3). The pendulous egg- 

 shaped blossom has a comparatively small opening. The 



