10 TOLERANCE OF PLANTS FOB SALTS IN ALKALI SOILS. 



Table II. — LimiU Uings of salts of magnesium and sodium. 



Critical concentrations. 



Go>sypium barba- Gossypium hirsu- 

 dense. " turn. 



Magnesium sulphate 0. 000312 normal 0. 000312 normal 



Magnesium chlorid 0004 normal .000312 normal 



im carbonate 005 normal .0025 normal 



Sodium sulphate 005 normal .005 normal 



Sodium bicarbonate 00625 normal .00375 normal 



- limn chlorid 00625 normal . 005625 normal 



The most marked difference in resistance between the two species 

 of Gossypium appears in the presence of sodium carbonate and sodium 

 bicarbonate. Egyptian cotton {Gossypium barbadense) can endure 

 twice as concentrated a solution of the carbonate and nearly twice as 

 concentrated a solution of the bicarbonate as can Upland cotton (G. 

 hirsutum ). In resistance to magnesium chlorid and to sodium chlorid. 

 also. Gossypium barbadenst is slightly superior to G. hirsutum,. 



RESULTS WITH SORGHUM I ANDROPOGOX SORGHUM' 



Four different varieties of Andropogon sorghum, designated by the 

 popular names of the varieties, were tested. 



Table III. — Limits of endurance of sorghum si salts of magnesium and sodium. 



-alts used. 



Critical concentrations. 



Early Amber. 



Dwarf Milo. 



Edra. 



Dagdi Juar. 



Magnesium chlorid 0. 00625 normal 0. 00375 normal 0.003 normal 0. 00125 norma! 



Magnesium sulphate 0085 normal .00625 normal .00625 normal .00375 normal 



Sodium carbonate 00625 normal .0075 normal .007 normal .00625 normal 



Sodium bicarbonate 009 normal .0125 normal .01 normal . 0OS75 normal 



Sodium sulphate 015 normal .013 normal .0125 normal .0125 normal 



Sodium chlorid 01S normal .01-4 normal .015 normal .015 normal 



The difference in toxicity between sodium chlorid and sodium sul- 

 phate is hardly appreciable in the case of this plant. In the presence 

 of magnesium chlorid there is more difference in resistance between 

 the different varieties than in the presence of magnesium sulphate. 



All except the Early Amber variety can endure a greater concentra- 

 tion of sodium carbonate thau of magnesium sulphate, and with this 

 exception the order of toxicity of the different salt- is that given in 

 the table. 



The Dwarf Milo variety of sorghum is on the whole less resistant to 

 the toxic influences of the various salts than the Early Amber. Magne- 

 sium chlorid brings out the most noticeable difference in this respect, 

 the Early Amber showing as much resistance to a concentration of 

 0.006^5 normal of this salt as the Dwarf Milo does to 0.00375 normal. 

 To -odium bicarbonate the Dwarf Milo is more resistant than the 

 Early Amber. To the other salts the two varieties are almost equally 

 resistant. 



113 



