Chap. X] EDAPHIC INFLUENCES IN TEMPERATE ZONES 657 



other plants make greater demands. The same character exists in other 

 Ericaceae — for example, Arctostaphylos Uva-ursi, Erica Tetralix, and, in 

 the west, E. cinerea, Vaccinium Vitis-Idaea, V. uliginosum, and V. Myrtillus 

 — which therefore accompany the heather, sometimes in drier stations, at 

 other times in moister ones. But also small trees, shrubs, and herbs 

 belonging to other families occur as accessory occupants of the heath, for 

 instance Juniperus vulgaris, Sarothamnus scoparius, Genista pilosa, G. ger- 

 manica, G. tinctoria, Cytisus sagittalis, Betula alba, Salix aurita, S. repens, 

 Aira fiexuosa, Molinia coerulea, and other grasses. All these plants also 

 occur in other stations, in some cases on dry sterile soil, in others on acid 

 humus, on moors and in thinly stocked woods. 



The predominance of the evergreen heather imparts to the heath some 

 likeness to the poorest sclerophyllous formations of the warmer districts 

 with moist winters. There is indeed a certain climatic analogy between 

 them ; like the sclerophyllous woodland, heath is dependent on moist winters 

 and thrives well only where the air is moist also in summer. The differences 

 however preponderate. Sclerophyllous woodlands give rise to pronounced 

 climatic formations which dominate the districts they occupy and exhibit 

 a far-reaching independence of the soil, whereas heath is confined to sand 

 and peat. Moreover sclerophyllous woodland is almost exclusively com- 

 posed of evergreen species which belong to the most diverse systematic 

 types, even to those that in other climates are deciduous ; in them the 

 evergreen character is clearly a climatic adaptation. The heath, on the 

 other hand, includes numerous forms that are leafless in winter, and 

 the evergreens belong to systematic types (Ericaceae, Coniferae) in which 

 the evergreen character is hereditary and has been retained in most of the 

 species under the most varied climatic conditions, even in the midst of 

 deciduous vegetation. The evergreen foliage is not an adaptation to the 

 environment in the heath, but a morphological feature of some of the species 

 of plants inhabiting the heath, specially of Calluna, and it dominates the 

 whole formation solely on account of the preponderance of Calluna. 



4. MOORS. 



Rich formation of peat on wet soil leads to the production of moors, 

 which occupy very large areas, specially in the cool and moist districts of 

 the cold temperate belt. In the warmer belts, owing to the more rapid 

 decomposition of vegetable matter, the formation of a massive layer of peat 

 is less frequent. 



Moors possess a very dissimilar vegetation, according as their mineral 

 substratum is poor or rich in lime. Moors poor in lime are named 

 high-moors, moors rich in lime are named meadow-moors. The water of 

 a high-moor is coffee-coloured and rich in organic matter, because it contains 



SCHIMPER U U 



