PLANT ASSOCIATIONS 231 



rainfall high, moisture excessive, 

 and drainage slow (p. 251). 



(e) Myrica-Bog (p. 253). 



(/) Sphagnum-Bog (p. 253). 



(g) Vaccinium-Moor. — In alpine zone, 

 replacing heather-moor, Erio- 

 phorum-moor, and grass-heath 

 (p. 255). 



4. Wet soils with much organic matter : 



Juncus and Carex-Bogs (p. 246). 

 6. In water : 



Vegetation of Highland Lochs and Moor- 

 pools (p. 238). 



C. Associations with Salt- Water. 



1. Dry soUs : 



(a) Sand-dune Ridges (p. 281). 

 (&) Rocks and Cliffs (p. 283). 



2. Wet sotIs: 



Salt-Marshes and Estuarine Marshes (p. 278). 



3. In water : 



Maritime Aquatic Vegetation (p. 275). 



In "Types of British Vegetation," edited by A. G. 

 Tansley, the plant associations occurring in the British 

 Isles are grouped into fourteen formations, a summary 

 of which is given below : 



I. Plant-formation of Clays and Loams. — Soil damp, 

 poor in lime. Associations: (1) pedunculate oakwood; 



(2) scrub; (3) grassland; (4) rush. 



II. Plant-formation of Sandy Soil. — Soil coarse and 

 dry, frequently poor in nutritive salts and tending to 

 become acid. Associations: (1) dry oakwood; (2) scrub; 



(3) grass-heath. 



III. Heath Formation. — Soil sandy or gravelly, with a 

 surface layer of dry peat, rainfall heavier than in H. Asso- 

 ciations : (1) oak-birch- heath; (2) heath; (3) pine-wood. 



IV. Plant-formation of the Older Siliceous Soils. — 

 Soil shallow, fine-grained and greasy when wet; forms 

 " mild humus " when well aerated and wet acid peat when 

 badly aerated, damp or wet; non-calcareous. Associa- 

 tions: (1) Sessile oakwood; (2) birchwood; (3) scrub; 



(4) mat-grass; (5) moor-grass. 



