6i8 



RELATION TO ENVIRONMENT. 



or less submerged. With many of these plants the upper parts 

 are above the water. Because of the large salt content in the 

 water the plants absorb it with difficulty. The aerial parts then 

 are provided with leaves and stems which retard transpiration. 

 They are thus xerophytic in structure and habit, but are often 

 called halophytes because of their adaptation to a large salt con- 

 tent in the salt water. A similar flora is found around salt 

 springs. For example, the maritime ruppia (Ruppia maritima), 

 a plant found in brackish water along the seacoast, occurs in 

 the water near salt springs in Onondaga County, New York, 

 and also in alkaline basins in the West, while Salicornia, etc., 

 occur on the ground in the same regions. Characteristic salt 

 marshes are the meadows with marsh-grasses. The mangrove 



Fig. 532. 



Plants marching into the sea. They have advanced from the trees at the left 

 in about two hundred years. Meadow in salt marsh. 



swamp is also a characteristic one, but this is treated of in forest 

 societies. Ganong in an important paper has shown how much 



