REGIONAL DISTRIBUTION 



499 



physiologically dry. On such soils the vegetation is composed 

 of halophytes, or plants which tolerate a larger proportion of' 

 mineral salts in the soil than can be endured by most plants. 1 

 One of the best-known halophytes is the common garden 

 asparagus, which sometimes has its growth increased by the 

 addition of common salt to the soil in which it is growing. 



FIG. 372. Plants taking possession of recently formed islands in a river 

 Along the bank at the right are three zones of woody plants 



In many points of form and structure halophytes usually 

 resemble ordinary xerophytes, and many of them are fleshy- 

 stemmed or fleshy-leaved. Such plants abound in the salt 

 marshes of the Atlantic coast and in some of the " alkali " 

 tracts of the extreme Southwest. 



1 For example, young seedlings of the saltwort (Salsola Kali, var. tenui- 

 folia), a typical halophyte, live longer in a 5.5 per cent solution of common 

 salt than most herbaceous mesophytes can in a 1.5 per cent solution. In 

 other words, the tolerance of Salsola for common salt is at least four times 

 as great as that of most herbs. 



