12 TOLERANCE OF PLANTS FOE SALTS IN ALKALI SOILS. 



Table V. — Limits of endurance of sugar-beet seedlings of salts of magnesium and sodium. 



Salts used. 



Critical concert- 

 tration. 



Salts used. 



Critical concen- 

 tration. 





0.0005 normal ] 









. 0005 normal 

 . 00625 normal j 



Sodium sulphate 







Sodium chlorid 











To the sugar beet sodium sulphate in pure solution is three times 

 as toxic as sodium chlorid and only a little less toxic than sodium car- 

 bonate. The two magnesium salts are more than ten times as toxic as 

 is sodium carbonate. 



COMPARISON OF RESULTS WITH EIGHT SPECIES IN PURE SOLUTIONS. 



In Table VI are brought together the results with pure solu- 

 tions for all the species of plants so far investigated, the figures 

 given being in each case the fraction of a normal solution repre- 

 senting the concentration of solution that allows the root tips of about 

 one-half the total number of seedlings tested to retain their capability 

 of further elongation after twenty-four hours of exposure to the 

 solution. 



Table VI. — Critical concentrations of pure solutions for eight species of plants. 





Plants tested. 



Salts used. 



Lupinus albus 

 (white lupine).* 



Medi- 



cago sa- 

 tiva (al- 

 falfa). 



Triticum 

 vulgare 

 (wheat). 



Zea 



mays 



; maize;. 



Andro- \ Gossy- 

 pogon A vena pium bar- 



Beta 



vul- 





Series 1. 



Series 2. 



(sor- ; (oats) . 

 ghum). 



(cotton). 



garis 

 (beet). 



Magnesium sul- 

 phate 



Magnesium chlorid 



0. 00125 

 .0025 

 .005 

 .0075 

 .02 



.02 



0.007 

 .0075 

 .0125 

 .04 



.045 



.03 



±0. 001 

 ± .002 



0.0C5 

 .005 

 .0125 

 .04 

 .045 



.025 



0.25 

 .08 

 .015 

 .05 

 .04 



.05 



0.00375 ! 0.001875 

 .00125 j .001875 

 .00675 : .00625 

 .0125 < .0175 



. 015 . 02 



0. 000312 

 . 0004 

 .005 

 .005 



0. 0005 

 .0005 

 . 00625 



Sodium sulphate.. 





. 00875 





. 00625 . 095 



Sodium bicarbon- 





.00875 .0075 006 '5 0075 

















*The experiments with Lupinus albus by Kearney and Cameron that were described in Report 

 Ko. 71 of the United States Department of* Agriculture, and of which the results are given in the 

 column headed "Series 1" of Table VI, were repeated two years later by Harter, using a fresh lot of 

 white lupine seed which, like the first, was obtained from Vilmorin, Andrieu & Co. in Paris. The 

 critical concentrations worked out in this second series of experiments (as shown in the table) are 

 much higher than those obtained in the first experiments. That this was largely due to the use of 

 fresher seed was proved by repeating the experiments a third time, using seed of the same importa- 

 tion as that in series 2, but a year older. In this third series of experiments the results agreed more 

 closely with series 1 than with series 2, the critical concentrations having been determined as follows: 

 Magnesium sulphate, 0.002 normal; magnesium chlorid, 0025 normal: sodium carbonate. 0.0125 nor- 

 mal; sodium sulphate, 0.02 normal; sodium chlorid, 0.0175 normal; sodium bicarbonate, 0.015 normal. 

 The order of toxicity of the different salts is very nearly the same in the three series, the principal 

 difference being that in the second and third sodium chlorid is slightly more toxic than sodium sul- 

 phate, and sodium bicarbonate than sodium sulphate and chlorid. It is noteworthy that the critical 

 concentrations in mixed solutions (containing calcium sulphate) were practically the same with the 

 second lot of seed, even when fresh, as with the first, notwithstanding the great differences in the 

 resistance of the two lots to pure solutions (see the second note to table on page 15). 



The limits for Medicago sativa in pure solutions were worked out 

 for the two magnesium salts alone, and with these the results are only 

 approximate. Those for Triticum vulgare were obtained by Harter 

 with the Chul variety of wheat. In the case of Andropogon sorghum 



113 



