1911-12.] BOTANICAL SOCIETY OF EDINBURGH 83 



laterally on its flanks. It gradually loses its identity in 

 the bracken association of the fixed dunes. Distributed 

 throughout these chief associations are minor associations 

 which are of local occurrence. Rubus ccesius, the dewberry, 

 for instance, forms a community of this description. This 

 species occurs in certain situations on the dunes, and re- 

 presents, with Pteris and Salix, the last stages in succession. 

 Sometimes associated with it is a hybrid form of Rubus 

 which gives rise to hummocks. In addition to these prin- 

 cipal associations many sub-associations and plant societies 

 exist. These will be described at a later stage. 



The term " j^lant association " implies a plant community, 

 and it therefore follows that the dominant types, mentioned 

 above, have associated with them species which may be 

 regarded as subdominant, abundant, or occasional, accord- 

 ing to the frequency of their occurrence. Some species are 

 apparently always associated with a particular dominant, 

 but on the dunes there are many cosmopolitan types which 

 are not limited in their distribution to any one association. 

 A list of subordinate species occurring in any one plant 

 community does not therefore imply that they are char- 

 acteristic of that association alone, or that they do not 

 occur as frequently in any other association. The majority 

 of associated species colonise the sheltered " flats " and dune 

 valleys which wind in all directions among the high dunes. 

 The configuration of these valleys is varied, and some are 

 characterised by a flora quite distinct in composition from 

 that of a neighbouring depression. Some are marsh-like 

 in character, while others are undulating plains of blown 

 sand, with embryonic dunes in various stages of formation. 

 The species which occupy the dry hollows are psammo- 

 philous, although some, like Cnicus arven&is, which fre- 

 quently occurs, are as characteristic of other formations. 

 On the fixed dunes sward-forming plants and others are 

 associated with Pteris and Ammophilo . while many species 

 of moss form patches of bright green colour everywhere, 

 and are particularly obvious during the early spring. 



The following detailed description of the associations is 

 not intended to be exhaustive. Many problems arising out 

 of the distribution of the dependent species in this formation 

 have yet to be solved, and the listing of associated types is 



