56 



certain that nowhere in the field will these salts be fonnd to have 

 anj^thing like the poisonous effect which they severall}^ exert upon 

 the roots of plants immersed in water solutions. Nevertheless it is 

 only from such experiments, conducted under simplified conditions, 

 that we can draw conclusions as to the actual effect of the components 

 of alkali soils upon plant growth. 



It is very desirable that this line of investigation be continued and 

 extended. Further combinations, perhaps of more than two salts, 

 should be tested; an attempt should be made to imitate as closely as 

 possible natural soil conditions; plants in different stages of growth 

 should be tried, for in irrigated regions it often happens that a stand- 

 ing crop is exposed to a varying soil content of soluble salts at differ- 

 ent periods of its development. -Finall}^, it is highl}^ important that 

 the experiments be repeated with other plants of widely- different 

 relationship and, as far as possible, of actual agricultural importance 

 in the region concerned. For while we may assume for the present 

 that the same sequence of harmfulness of the several salts will obtain 

 in the case of most or all ordinarilj^ cultivated plants, this is oi5en to 

 doubt, and it is quite certain that the actual limits of endurance differ 

 in the case of different plants. 



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