124 BOTANICAL GAZETTE [februak 



beach, and in many cases the occurrence on the upper beach of plants 

 belonging to the middle beach can only be explained by their having 

 been blown landward from the original position. 



The vegetation on the upper beach consists principally of perennial 

 herbs, shrubs, or low trees. The tension line toward the littoral 

 dune is not so marked as in the direction of the middle beach, but 

 where no dune formations are developed the upper beach usually 

 borders upon a forest. In the latter case it often happens that inland 

 plants have wandered out to the sea-shore formations, while it never 

 happens that sea-shore plants have been able to establish themselves 



inland on the meadow or forest that usually follows the strand forma- 

 tions. 



The littoral dune is much exposed to the wind, its moisture content 

 is low, constant oxidation of organic water goes on, and the tempera- 

 ture is lower than on the upper beach, because of more intense 

 radiation. The soil is very loose, shifting, and sterile (fig. 9). The 

 vegetation shows the results of these conditions very plainly. It i 

 prostrate and dwarfed in habit, scattered and poor in variety of 

 form 



>. 



The active dune (the white dune of Warming) 



istics of the littoral dune in excess, and its vegetation is generally still 

 more monotonous. Some difference can be observed in regard to the 

 plants on the slope and summit of the dunes. It is usually richer in 

 species on the latter part of the formation. 



Warming) is formed 



,j „„,„, VLI1C g l<X y uiUie OI V V A KM1JN (?) li> IW"""" " 



greater distance from the sea, where the sand has to some extent cor 

 solidated, and a heather vegetation has been established. Forma- 

 tion of humus goes on, the plants grow closer and closer, mosses or 

 lichens occupy the ground between the higher plants, and final! 

 the soil is completely covered with a carpet of vegetation. Th 

 heather association is the final stage in the series of sand-plant com- 

 munities beginning on the small embryonic dunes to leeward from the 



ndy field 



able 



mations mentioned. It has a comparatively level surface, is better 

 to retain moisture, and has a higher temperature. The sand grain* 

 are of such uniform size as to prevent ripple or dune formation, and 



