KEARNEY: PLANT LIFE ON SALINE SOILS 119 



require corresponding powers of accommodation in the absorb- 

 ing organs of the plant. A thorough investigation of the water 

 economy of desert halophytes is, therefore, much to be desired 



OSMOTIC PRESSURE IN ROOTS AND LEAVES 



Comparatively few determinations have been made of the 

 osmotic pressures in the roots of halophytes. The data at 

 hand indicate that, at least under the comparatively favorable 

 conditions of coastal salt marshes, the plant is easily able to 

 cope with the problem of absorption. Thus Hill found that the 

 root hairs of Salicornia can develop a pressure corresponding to 

 that of an 8.7 per cent solution of sodium chloride, which is 

 probably equivalent to about 65 atmospheres. 



As regards halophytes that inhabit arid regions, determina- 

 tions appear to have been made only on the leaves and stems. 

 In ordinary mesophytic plants of temperate climates the osmotic 

 pressure of the leaf cells seldom exceeds 30 atmospheres and is 

 usualh' much lower than this. But pressures up to 100 atmos- 

 pheres were detected in the leaves and stems of salt plants by 

 Cavara in Italy and by Fitting^^ in the Sahara Desert. Ruhland 

 was able to develop, in the leaves of Statice Gmelini, a pressure 

 which he estimated at 165 atmospheres. ^2 



It is not improbable that the absorbing roots of desert halo- 

 phytes ceage temporarily to function when, as doubtless often 

 happens, the osmotic pressure of the soil solution greatly ex- 

 ceeds 100 atmospheres. Miss Halket's^^ observation that when 

 the salt content of the soil solution reached 17 per cent, plants 

 of Salicornia remained alive and apparentl}^ uninjured but 

 ceased to grow, points in this direction. 



There is abundant evidence of the ability of halophytes to 



^'- H. FiTTiXG. Die W asserversorgung und die osmotischen Druckuerhdltnisse 

 der Wustenpflanzen. Zeitschr. Bot. 3: 209. 1911. 



^- It does not follow that equally high pressures would have been detected in 

 the roots, since comparative determinations upon different organs of the same 

 individual plant have shown, in numerous cases, that the osmotic pressures of 

 the root cells are lower than those of the leaf cells. 



^^ A. C. Halkett. The effect of salt on the growth of Salicornia. Annals of 

 Botanv 29: 143. 1915. 



