35 TOLERANCE OF PLANTS FOE SALTS IN ALKALI SOILS. 



The results have established the fact that different genera and species 

 differ greatty in their power of resistance to the salts of magnesium 

 and sodium that are common in so-called alkali soils, and that further- 

 more different varieties, or even mere agricultural strains of the same 

 species, possess marked differences in this respect. In mixed solu- 

 tions, especially in the presence of a salt of calcium, these differences 

 are much less pronounced, but still exist in such a degree as to leave 

 do escape from the conclusion that some species and varieties of plants 

 are better adapted than others to growing in soils containing relatively 

 large amounts of these salts. Since very marked differences in toler- 

 ance exist between different individuals of the same strain or variety, 

 there is obviously an opportunity for an increase of this quality by 

 artificial selection. 



In the present paper the results of experiments with single (pure) 

 solutions in their effect upon maize, sorghum (four varieties), oats 

 (two varieties), cotton (two species), and sugar beets are first described. 

 The resistance to pure solutions of these plants and of the white lupine, 

 alfalfa, and wheat are next compared. The effect of an excess of cal- 

 cium sulphate in neutralizing the toxicity of the magnesium and 

 sodium salts upon each of the plant species above mentioned, and 

 finally that of amounts of calcium sulphate smaller than an excess in 

 counteracting the toxic effect of these salts upon the white lupine 

 and upon sorghum are then treated. 



It should be emphasized that the results of these water-culture 

 experiments with pure solutions of a single salt or of two salts are not 

 to be directty compared with the results of observations, made upon 

 plants growing in natural "alkali" soils. In the latter case we have 

 always to deal with a mixture of several salts, and, moreover, the 

 presence of the soil itself introduces physical factors that modify in 

 various ways the effect of the solution upon plants. In these labora- 

 tory experiments the problem was purposely simplified by omitting 

 the soil, thus permitting us to ascertain directly the varying toxic 

 effect upon different plants of some of the principal "alkali" salts as 

 a necessary preliminary to the more complex problem of their toxicity 

 in the presence of the soil itself. In the experiments with mixed solu- 

 tions a step is taken in the direction of this greater complexity, and it 

 is noteworthy that the results obtained are in this case more nearly 

 comparable with the relations obtaining in nature than are those with 

 pure solutions. Experiments are now in progress in which cultures 

 in sand watered with the extracts from natural alkali soils and with solu- 

 tions of salts made up to imitate the alkali soil extracts, as well as in 

 the natural alkali soils themselves, are substituted for the water cul- 

 tures used in the experiments here described. 



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