124 KEARNEY: PLANT LIFE ON SALINE SOILS 



certain marine algae; and results obtained b}^ Benecke" indicate 

 that some of the Cyanophyceae may grow equally well if potas- 

 sium is completely replaced by sodium in the nutrient solution. 

 In regard to the nutrition of vascular plants, however, no fact 

 seems to be better established than the indispensability of a 

 minimum of potassium. On the other hand, it has never been 

 'proven that sodium is indispensable to any of the higher forms of 

 plant life. 



Although sodium is almost always found in the ash of plants, 

 it does not, as far as we know, enter into organic combination. 

 This would seem to indicate that plant life is not conditioned by 

 its presence as by the presence of potassium, phosphorus, and 

 magnesium. Nevertheless, it by no means follows that under 

 certain conditions sodium may not be an important factor in 

 growth. 



Different investigators of the fertilizer value of sodium salts 

 report widely divergent results, but it is impossible to ignore the 

 numerous instances in which beneficial effects have been observed, 

 especially where the soil is deficient in potassium in readily 

 available fomi.^^ 



Such effects are doubtless, in many cases, due chiefly to the 

 setting free by chemical reaction in the soil of the potassium of 

 relatively insoluble compounds. But even when such reaction 

 was excluded by growing the plants in water cultures or in quartz 

 sand, without the addition of potassium, sodium has been ob- 

 served to stimulate growth. 



It would seem, therefore, that when potassium is not avail- 

 able in sufficient quantity, some of the physiological functions 

 which are normally performed by that element may be assumed 

 by sodium. In regard to the nature of these functions, the . 

 following suggestions have been made: 



** W. Benecke. Ueber CuUurhedingungen einiger Algen. Bot. Zeitung 

 66:84-96. 1898. 



"•^ This has been the subject of long-continued investigation by the Rhode 

 Island Agricultural Experiment Station. The results have been published in 

 the annual reports for 1894 to 1908 and in bulletins 47, 104, 106, and 153. See 

 especially H. J. Wheeler and B. L. Hartwell {Concerning the functions of 

 sodium salts. R. I. Agr. Exp. Sta. Ann. Rep. 1906: 186-316. 1907). 



