482 



GENERAL MORPHOLOGY OF PLANTS 



xerophytes. Some of the plants accustomed to growing in such 

 localities are American sea-rocket, seaside spurge, bug-seed, sea- 

 blite, sea-purslane, the sand-cherry, dwarf willow, marram- 

 grass, certain species of beard-grass, etc. Third. Rocky shores of 

 areas. Here lichens and mosses first grow, later to be followed 

 by herbs, grasses, shrubs and trees, as decayed plant-remains 

 accumulate in the rock crevices. Fourth. Shores of ponds, or 

 swamp moors. Here the vegetation often takes on a zonal 



Fig. 425. 



Planting grasses on wind-swept sandy coasts to prevent movement of dunes into the 

 city, Southport, England. (Photograph by the author.) 



arrangement (zonation) if the ground gradually slopes to the 

 shore and out into the pond. In fig. 426 is shown zonal distri- 

 bution of plants. The different kinds of plants are drawn into 

 these zones by the varying amount of ground-water in the soil, 

 or the varying depth of the water on the margin of the pond as 

 one proceeds from the land towards the deeper water. On the 

 border lines or tension lines between the different zones, the 

 plants are struggling to occupy here ground which is suitable for 

 each adjacent individual formation. Other edaphic societies are 

 those of marl ponds, alkaline areas, oases in deserts, warm oases 



