336 NATURE AND PROPERTIES OP SOILS 



(1) the physiological constitution of the plant, and (2) the 

 rooting habit. The former is little understood, so much de- 

 pending on the character of the alkali solution, the nature 

 of the cell-wall, and the character and activity of the cell con- 

 tents. It has long been known that the toxicity of two salts 

 when together is considerably less than the sum of their detri- 

 mental action when used alone. This ameliorating or antagon- 

 istic action varies for diiferent salts, seeming to be greatest 

 when calcium and magnesium are involved. This is but an 

 example of the complexities which arise when an attempt is 

 made to study the physiological relationships of alkali injury. 



The rooting habit of plants in their relation to alkali toler- 

 ance is more easily understood. The advantage is always with 

 deep-rooted crops, such as alfalfa and sugar-beets, probably 

 because a portion of the root may be in a less strongly impreg- 

 nated part of the soil. 



The tolerance of many plants to alkali has been studied in 

 water culture. Such results are not of great practical value, 

 however, as it is only in soil that all of the numerous factors, 

 such as absorption, antagonism, and physical conditions, come 

 into play. Harris and Pittman ^ found that organic matter 

 in a soil had a marked ameliorating influence on alkali injury, 

 especially from sodium carbonate. High moisture was also an 

 important factor in lowering the toxicity of soluble salts. 



Guthrie and Helms,^ using a rich garden loam, found the fol- 

 lowing concentrations slightly affecting or entirely preventing 

 germination and growth of certain crops. (Table LXXVII.) 



Of the cereals, barley and oats are the most tolerant, these 

 being able, in some cases, to produce good crops in soil con- 

 taining two-tenths per cent, of white alkali. Of the forage 

 crops, a number of valuable grasses are able to grow on soil 



^Harris, P. S., and Pittman, D. W.^ Soil Factors Affecting the 

 Toxicvty of Alkali; Jour. Agr. Ees., Vol XV, pp. 287-319, 1918. 



^Gutiine, P. B., and Helms, R., Pot Expenments to JDetermme the 

 Limits of Endurance of Different Farm Crops for Certain Injurious Suh- 

 stances; Agr. Gaz., N. S. Wales, Vol. 14, No. 2, pp. 114420, 1903. 



