KEARNEY: PLANT LIFE ON SALINE SOILS 117 



The gist of the matter is that manj^ halophytes that grow 

 under chmatic conditions favorable to intense transpiration, or 

 in soils subject to periodical drought, show xerophytic modifi- 

 cations; but high concentration of the soil solution does not 

 necessarily induce this type of structure if the cUmate is humid 

 and an abundance of soil moisture is normally present. 



WATER ECONOMY OF HALOPHYTES 



It has been repeatedly demonstrated that absorption of water 

 by the roots of nonhalophytic species is difficult or impossible 

 when the soil solution reaches such concentrations as are en- 

 countered in .the natural habitats of halophytes. When forced 

 to obtain their water from a relatively concentrated salt solu- 

 tion, ordinary- mesophj^tes, such as the common crop' plants, 

 show a marked decrease in transpiration and in photosynthetic 

 activity, resulting in diminished growth. 



Schimper-^ argued from the known behavior of nonhalophytes 

 when exposed to strong salt solutions, and from the assumed 

 xerophytic structure of all halophytes, that the latter are sub- 

 ject to the danger of injury from excessive accumulations of salt 

 in their assimilating cells,,and that protection against this danger 

 is secured by reduction of the transpiration. He later^^ modified 

 this view by attributing the supposed necessity for reduced 

 transpiration to the difficulty of absorption by the roots from a 

 strong salt solution. In his view a saline soil is "physiologically 

 dry," even when saturated with water. 



jMore recent investigations have demolished all of the pre- 

 mises upon which this theory rested. It has already been 

 pointed out that by no means all salt plants possess a transpira- 

 tion-reducing structure, so that we are justified in speaking of 

 halophilous mesophytes and hydrophytes, as well as of halo- 

 philous xerophytes. Species that inhabit dry saline soils in 

 arid regions doubtless find advantage in such structural modi- 

 fications as tend to diminish transpiration; but the researches of 



" A. F. W. ScHiMPER. Die indo-malayische Strandflora, p. 26. Jena, 1891. 

 -* A. F. W. ScHiMPER. Pflanzengeographie auf physiologischer Grundlage, 

 p. 100. Jena, 1898. 



