VEGETATION OF ROCKY PLACES. 619 



of the area covered by the salt marshes of the Bay of Fundy has 

 been converted into arable land, especially for the growth of hay. 

 The farmers in that section "dyke" the marshes to prevent their 

 being flooded during high tide. Many of the true salt-marsh 

 plant formations, as well as the conditions of environment, are 

 discussed. One of the most characteristic halophytes of the salt 

 marshes here is the sedge spartina (S. stricta glabra). It grows 

 on the shore down to the water's edge along the open ocean, and 

 here the plants are low and stunted, since they are subject to 

 the strong salt water during tide. It is also one of the characteris- 

 tic plants forming meadows in the brackish waters, and here it is 

 more luxuriant. It possesses true xerophytic structures, propa- 

 gates chiefly by subterranean shoots, and the stems and leaves 

 have ample air-spaces. The abundance of air in the plant enables 

 it to endure prolonged and frequent inundation by the tides. 

 Ganong has found by experiment that the root-hairs of a number 

 of seedlings of these salt-marsh plants resist plasmolysis when 

 immersed in quite strong saline solutions, and this probably 

 explains why it is these plants are able to grow in soil and water 

 of such salt concentration. 



1106. Shores of marl ponds. On the shores of marl ponds 

 the soil is calcareous, i.e., it contains large quantities of lime in 

 the form of carbonate of lime, mixed with sand and clay in vari- 

 able proportions in different localities. These shores often furnish 

 a characteristic vegetation which is usually xerophytic. On the 

 shores of marl ponds in New York the shrubby cinquefoil (Poten- 

 tilla fruticosa = Dasiphora fruticosa) is often one of the common 

 formations. The usual habitat for this species is in swamps and 

 rocky places from Labrador to Greenland and Alaska. (See 

 marl ponds in Chapter LVI.) 



