CHAPTER XV. 



HALOPHYTE SOCIETIES. 



169. General characters. The hydrophytes, xerophytes, 

 and mesophytes are distinguished from one another by the 

 amount of water accessible. This classification must be 

 regarded as largely artificial, often resulting in the natural 

 separation of closely related societies. For example, the 

 sphagnum -moor is a well-marked hydrophyte society, but 

 it holds a very close relation to the shrubby heath, which 

 is a xerophyte society. These two societies, however, are 

 kept separate on the basis of the water supply, but they 

 are brought together by similarity in the food material sup- 

 plied by the water. It becomes evident, therefore, that a 

 natural classification properly depends not so much upon 

 the amount of water, as upon what the water contains. 

 However, the three groups of societies already considered 

 have been used for the sake of simplicity. 



The halophytes, however, are characterized in a very 

 different way, for the condition which determines them 

 is not the amount of water supply, but the fact that the 

 water contains certain salts, notably common salt, gypsum, 

 and magnesia. The water may be abundant enough to rep- 

 resent hydrophyte conditions, or it may be scanty enough 

 to represent xerophyte conditions, but if these salts are 

 present in the soil in sufficient abundance to strongly 

 affect the water, the plants are halophytes. Such soils 

 are recognized in popular language as salt soils or alkaline 

 soils. 



Such areas occur in various positions : (1) in the 



