Active or wandering dunes. 
Easily blown about, because plant life is limited. 
Ist.. As dunes grow in height plants further from 
ground water. 
2nd. Only trees adapted to live there are short lived. 
Often very complex. 
Often cause great changes in the landward flora, sometimes 
causing great damage, which is sometimes successfully 
prevented by the planting of various dune formers. 
Rejuvenated dunes. ; 
Methods for checking movements of dunes. 
XIX. PLANT SOCIETIES OF ROCKY AREAS, MEADOWS, 
AND MARSHES. 
I. Vegetation of Rocky Places, and New Land. 
Rocky shores. 
Plants often modified by proximity to water (surf, etc.). 
Zonal arrangement on sloping shores. 
Azonal on irregular surface rock. 
Formations usually open. 
Lichens as pioneers in soil making. 
Succession of plants as soil is formed. 
Crevice plants. 
Lichens, Cladonia, with several species. 
Mosses, Hedwigia, Andraea (also on smooth rock). 
Ferns, Polypodium, Dryopteris, Pellaea, Asplenium. 
Herbs, harebell (Campanula), bluets (Houstonia), 
aium root (Heuchera).< 
Grasses, Arenaria stricta,) Agrostis hiemalis,. etc. 
Shrubs, Cornus, Spiraea, some cedars. | 
Trees, white pine, also P. divaricatus, ash, trembling 
poplar, etc. 
Transition of open formations into close ones. 
1. Treith1888. Volcano krakatau three years after moun- 
tain covered with lava. 
2. Schimper, Volcano Guntur in West Java mountains, 
in 1843 covered with glowing volcanic matter. 
Vegetation still quite open. 
Epiphytic shrubs and ferns here on ground. 
59 
