16 TOLERANCE OF PLANTS FOE SALTS IX ALKALI SOILS. 



than twice that for the white lupine. As an illustration of the ten- 

 dency to equalization of the toxic effects of the different salts in the 

 presence of calcium sulphate may be mentioned the fact that in pure 

 solutions the sugar beet will endure fifty times as much of sodium 

 chlorid as of magnesium chlorid, while the addition of calcium sulphate 

 makes the critical concentration of both salts the same for this plant. 

 In some cases the relative resistance of two plants is reversed in the 

 presence of calcium sulphate. Thus, sorghum is more resistant than 

 cotton to pure solutions of magnesium chlorid and of sodium chlorid, 

 but to the mixed solutions cotton is the more resistant. Oats are twice 

 as sensitive as wheat to a pure solution of sodium carbonate, but to 

 sodium carbonate plus calcium sulphate wheat is four times as sensi- 

 tive as oats. 



NEUTRALIZING EFFECT OF SMALLER AMOUNTS OF CALCIUM SULPHATE. 



In all of the previously described experiments with mixed solutions, 

 the solutions of magnesium and sodium salts were saturated with the 

 neutralizing agent (calcium sulphate), which was added in excess as a 

 solid. 



It was therefore desirable to ascertain whether smaller amounts of 

 calcium sulphate would not neutralize the toxic action of the various 

 salts employed in pure solutions. Two series of experiments were 

 carried out to determine this point, the first with Liqyhms alhus, the 

 second with the Dagdi Juar variety of Androjiogon sorglium. In the 

 first series sodium chlorid was selected as the salt to be neutral- 

 ized, while in the second results were obtained with sodium chlorid, 

 sodium carbonate, and magnesium chlorid. 



RESULTS WITH LUPIXTS ALBUS. 



Aqueous solutions of calcium sulphate of definite concentrations 

 were added in equal volume to a solution of sodium chlorid, the con- 

 centration of the latter being varied until that was ascertained which 

 represented the critical concentration for the root tips of the lupine 

 seedlings in the presence of the amount of calcium sulphate that was 

 added. A different method was followed in securing the maximum 

 amount of calcium sulphate (3.69 grams per liter), an excess of cal- 

 cium sulphate being in this case dissolved in various concentrations of 

 the sodium chlorid solution itself, a and the latter being then tested 

 until the critical concentration was ascertained. The limits for sodium 

 chlorid in the presence of different amounts of calcium sulphate are 

 stated both in grams per liter and in fractions of a normal solution of 

 sodium chlorid present in the mixed solutions that were found to be 

 critical. 



a Calcium sulphate is of course much more soluble in a solution of sodium chlorid 

 than in pure water. 



113 



