SOIL RELATIONS 251 



pies from cultivated fields were also made which 

 showed that wheat grew well in presence of 0.137 per 

 cent of sodium carbonate, but was destroyed by 0.2 per 

 cent. The carbonate (" black alkali ") was found most 

 harmful, and the sulfate (" white alkali ") least harmful. 

 Legumes were more affected than cereals. Two per cent 

 of carbonate in soil around the roots was fatal to cereals. 



Black alkali is said to be more serious : (1) because of 

 its corrosive effect on the plant at the crown, and (2) be- 

 cause of its " puddling " action on the soil, making it 

 difficult of tillage. 



Harter determined that the degree of injury to 

 wheat seedlings by toxic salts decreases in the order, 

 magnesium sulfate, magnesium chloride, sodium car- 

 bonate, sodium bicarbonate, sodium sulfate, and sodium 

 chloride; that wheat varieties from humid regions 

 are less resistant; that resistance varies greatly in in- 

 dividuals of the same variety ; and that the same toxic 

 salts act as stimulants in dilute solutions. 1 Kearney 

 and Harter (1907), in later experiments, found (1) great 

 variation in different species of the same family and 

 different varieties of the same species in their degree of 

 tolerance of alkali salts ; (2) that calcium sulfate in excess 

 in the same solution greatly diminishes the toxicity of 

 magnesium and sodium salts, in case of all plants tested ; 

 and (3) that the comparative resistance of plants and 

 salts in mixed solutions comes* nearer that observed in 

 connection with combinations of alkali salts occurring 

 naturally in western soils than when these plants are 

 grown in pure solutions of single salts. Wheat was 



1 The author also obtained the same results with toxic salts 

 in dilute solutions in experiments with spores of the rust 

 fungi. 



