198 



PLANT SOCIOLOGY 



(see p. 231). This last characteristic association endures the greatest 

 and most continuous salt concentration. It covers the otherwise 

 plantless salt pans, which are flooded in winter and in summer crack 

 into characteristic polygonal columnar structures (Fig. 118). 



Algal communities of Microcoleus chthonoplastes and Lyngbya 

 appear as pioneers upon bare, occasionally flooded (by sea water) 



Fig. 106. 



T^i.LCt of 11 



ill the Camargne, 



Irance. 



muddy and sandy soil on northern European coasts as well as about the 

 Mediterranean Sea. Warming and Grabner (1918) mention communi- 

 ties of blue-green algae and diatoms on the sandy coasts of Denmark, 

 which, with their mucous sheaths and membranes, glue together the 

 grains of sand into crustlike masses just beneath the sandy surface. 

 These pioneer associations contribute to the development of the upper- 

 most soil layer and afford favorable germinating beds for higher plants. 



