THE ECOLOGY OF PLANTS. 449 



oak-wood may consist of a Pteris-Scilla-Holcus Association, 

 in which Bracken, Bluebell, and Yorkshire Fog together 

 cover a large area (Fig. 182) ; again it may be a Calluna- 

 Vaccinium [Heather and Bilberry] Association, or one of 

 several others." 



Dr. Smith gives the following specimen list of plants in a 

 survey : 



" Larch- wood, with a few Spruces, trees about 70 feet high 

 and from 6 to 10 feet apart ; two distinct associations found 

 Calluna and Bracken, the latter in hollows, the former 

 occupying the larger, more level floor of the wood. Soil 

 thin peaty humus, overlying Liassic Limestone, 650 feet 

 alt., Clevelands, W. Yorks. 



Calluna Association : 

 Social species : 



Dominant, Calluna vulgar is 40-50% ) 



Erica cinerea 20-30% [ about 70%' 



Sub-dominant, Vaccinium myrtillus 5-10% ) 



Festuca wina 

 Air a flexuosa 

 Agrostis vulgaris 

 Anthoxanthum 



Isolated species : 



Characteristic: Potentilla tormentilla, Galium saxatile, 



Oxalis acetosella, etc., in decreasing abundance. 

 Sporadic: Carduus arvensis (from farm-land)." 



Other well-marked formations are (1) deciduous woods, 

 e.g. Beech, Oak, Birch ; (2) coniferous woods, e.g. Scots 

 Pine; (3) xerophilous, herbaceous, and undershrub vegeta- 

 tion, e.g. heather moor, cotton-sedge moor or moss, grass- 

 land (on chalk downs, etc.), grass-heath (grasses like hardus 

 mixed with such heath-plants as Ling, Heaths, Bilberry, 

 etc.); (4) maritime vegetation, including sand-dunes, salt 

 marshes, shingle beaches, sea-cliffs. 



1 These percentages are estimated by eye according to the propor- 

 tion of ground in a small sample area covered by the different forms of 

 vegetation. 



8. B. 29 



about 30%' 



