9 



have long been under cultivation or, in the lowest hollows where there 

 is most moisture, used as hay fields. 



Some few low spots are filled with water the whole year round 

 and here we find a hydrophyte formation (Potamogeton 

 natans, P. gramineus, Myriophylfum, Littorella, Lobelia, Helosciadium. 

 inundation, Scirpus fluitans and others) and a h e 1 o p h y t e for- 

 mation (chiefly of Cyperaceae: Carex rostrata, C. Goodenoughii, 

 Scirpus Tabernaemontani, Heleocharis palustris and H. multicaulis; 

 further Polygonum amphibium, Glyceria fluitans, Phragmites, Meny- 

 anthes, Comarum and others) ; then follows as a rule a Cyperaceae 

 mars h. Many hollows are filled with water for a longer or 

 shorter period of the year, but not in the summer time; according to 

 the amount of moisture in the bottom of these they are usually covered 

 either by Littorella uniflora, Heleocharis multicaulis or Aira setacea.. 

 Ascending from the dampest spots up to the top of the low dunes, we 

 pass a series of different plant associations, whose position is deter- 

 mined by the requirements of the species composing them with regard 

 to the moisture in the soil; as examples may be mentioned, progressing 

 from moister to drier ground: 



1. Littorella association. 



2. Heleocharis multicaulis association, with Ra- 

 nunculus flammula etc. 



3. Aira setacea association. 



4. Lower Cyperaceae marsh, especially of Rhynchospora 

 fusca. 



5. Higher Cyperaceae marsh, especially of Carex 

 Goodenoughii and C. panicea; further Drosera, Potentilla erecta, 

 Lycopodium inundatum. 



6. Erica heather moor: Erica tetralix, Calluna vulgaris, 

 Empetrum nigrum, Vaccinium uliginosum, Genista anglica, Salix 

 repens, Potentilla erecta etc.; here also the rare Carex trinervis. 



7. Calluna heath; in addition to Calluna, Salix repens, Em- 

 petrum, Genista anglica, Vaccinium uliginosum etc., often also 

 many herbs, most often Festuca ovina, Nardus stricta, Antho- 

 xanthum. 



8. Thymus-Salix- P s a m m a dunes. 



9. P s a m m a dunes. 



Naturally, the extension of the various associations varies according 

 to the greater or less slope of the ground, and where the bottom of 

 the hollows is relatively high, one or several of the associations 

 mentioned are of course wanting; further, we find differences in the 

 associations or belts, which are due in part at least to the influence 

 of man, for example harvesting of hay and heather (Ling) or to 

 grazing: the chamaephytes (small shrubs) of both the Erica and Cal- 



