ALKALI SOILS 



335 



solving the parts of the plant with which they come into con- 

 tact. Such action is not as important as plasmolysis and when 

 it does occur is most noticeable at the root crown. (See 

 Fig. 55.) 



Indirectly, alkali may influence plants by its effect on soil 

 tilth, soil organisms, and fungous and bacterial growths. Mar- 

 chal, 1 for example, found that the formation of nodules, con- 

 taining the nitrogen-fixing organisms, did not develop well 



Fig. 55. — )(1) Cross-section diagram of a normal plant cell, 

 after plasmolysis has taken place. 



(2) Cell 



on pea roots in nutrient solutions when certain concentra- 

 tions of salts were maintained. Ammonium salts were injuri- 

 ous at a concentration of 500 parts per million. Potassium and 

 sodium salts retarded the nodule development at 5000 and 3333 

 parts to the million respectively. The quantity of alkali that 

 will cause injury to ammonifying and nitrifying bacteria 

 varies from 250 to 4000 parts per million, depending on con- 

 ditions. 



177. Resistance of different plants to alkali. — The fac- 

 tors that determine the tolerance of plants toward alkali are : 



1 Marchal, E., Influence des Sels mineraux nutritifs sur la Production 

 des nodosites chez le Pois; Compt. Bend. Acad. Sci. (Paris), Tome 133, 

 No. 24, p. 1032, 1901. 



