110 Kearney: plant life on saline soils 



with normal or dilute sea-water and the salts present are such as 

 occur in the ocean. 



In arid regions away from the coast, the accumulation of salts 

 is due to local erosion. Owing to the scantiness of the rainfall, 

 the saline components of the country rocks are not, as in humid 

 regions, carried away by rivers flowing into the ocean. Instead 

 they are transported short distances by the surface and under- 

 ground drainage channels and become accumulated in the bot- 

 toms of the valleys and of closed basins. In this way are formed 

 the salt lakes and the alkali flats, covered during the dry season 

 with a glistening white crust of salts, which are so characteristic 

 a feature of arid countries the world over. 



Sea-water is practically uniform in the nature and proportion 

 of its different salts and the same is necessarily true of the soil 

 of coastal marshes. In both cases, sodium chloride strongly 

 predominates. On the other hand, the saline components of 

 soils in arid regions vary with the composition of the rocks 

 from which they were derived. Salts of sodium (chloride, sul- 

 phate, carbonate, bicarbonate) are usually the most abundant, but 

 the corresponding salts of potassium, magnesium, and calcium 

 are commonly also present. 



Since each salt, when presented in a pure solution, has its 

 specific toxicity for plants, it might be thought that correspond- 

 ing differences would be observed in the vegetation of ''alkali" 

 soils of different chemical composition. But there is little evi- 

 dence that such is the case. The reason doubtless is that the 

 solution in saline soils, like the water of the sea, is a "balanced" 

 solution, in the sense of Loeb and Osterhout.'- It rarely hap- 

 pens, in arid regions, that soluble salts occur in large quantity 

 where the soil is deficient in calcium ; and the presence of calcium 

 equalizes, in large measure, the different toxicities shown in pure 

 solutions by salts of the other bases.^ Consequently, it is usu- 



2 W. J. V. Osterhout. On the importance of physiologically balanced solution- 

 for plants. Bot. Gaz. 42:127. 1906; also 44:259. 1907. The same investiga 

 tor has developed the subject in numerous subsequent papers. 



^ T. H. Kearney and F. K. Cameron. Some mutual relations between alkali 

 soils and vegetation. U. S. Dept. Agr. Rept. 71:7-60. 1902. T. H. Kearney 

 and L. L. Harter. The comparative tolerance of various plants for the salts com- 

 mon in alkali soils. U. S. Dept. Agr. Bur. Plant Ind. Bull. 113. 1907. 



