54 



more sharply in the presence of the carbonates of soda than when 

 other "alkali" salts are concerned. 



So great appears to be the promise of resnlts to be obtained by breed- 

 ing alkali-resistant races of the more important field crops of the far 

 western United States, that the Department of Agriculture has already 

 undertaken work on this line. During the past season experiments 

 with this end in view were begun under the direction of Mr. Webber, 

 of the Plant-Breedintr Laboratory, Division of Vegetable Physiology 

 and Pathologj^ It is hojied that they will demonstrate the practical 

 value of this method of approaching the problem. 



SUMMARY. 



As the result of these preliminary studies, the following facts can 

 be regarded as established: 



(1) Those readily soluble salts of magnesium and of sodium which 

 are characteristic components of alkali soils are exceedingly^ injurious 

 to plants when exposed to pure solutions of them of concentration 

 above a minimum which is specific for each. 



(2) They are toxic in the following sequence, beginning with the 

 most harmful: Magnesium sulphate, magnesium chloride, sodium car- 

 bonate, sodium sulphate, sodium chloride, and sodium bicarbonate. 



(3) Calcium chloride in pure solution is ten times less injurious 

 than sodium chloride, and two hundred times less injurious than 

 magnesium sulphate, if chemically equivalent solutions are considered. 



(4) Magnesium carbonate in a saturated solution is not markedly 

 Injurious, while magnesium bicarbonate in saturated solution acts as 

 a strong poison. Calcium carbonate and calcium sulphate are posi- 

 tively stimulating in saturated solutions, while calcium bicarbonate 

 appears to be decidedly injurious. 



(5) The toxic effect of the injurious salts is due very much more to 

 the influence of the cathions (derived from the basic radicle) than to 

 the anions (furnished by the acid radicle). 



(6) By mixture of equal volumes of two readily soluble salts, or by 

 the addition of a solid excess of a relatively insoluble to a solution 

 of an easily soluble salt, the toxic effect of the more harmful compo- 

 nent can in a majority of cases be diminished, or the concentration of 

 the more toxic salt endurable by the roots of plants can be increased. 



(7) This increase is much greater in cases where a different kind of 

 cathion is added to the solution than when a new anion onlj^ is 

 introduced. 



(8) Addition of sodium ions to a solution containing magnesium 

 ions in most instances markedly weakens the toxic action of the latter. 



(9) Addition of calcium ions to solutions containing either sodium 

 or magnesium ions nearly always counteracts to an extraordinary 

 degree the injurious effect of the sodium or magnesium ions, this 

 beneficial influence being usually much more marked when calcium 

 is furnished as the sulphate than when the chloride is added. 



