ALKALI SOILS 



335 



solving the parts of tlie plant witli 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,^ for example, found that the formation of nodules, con- 

 taining the nitrogen-fixing organisms, did not develop well 



Fig, 55. — /(I) Cross-seetion diagram of a normal plant cell. (2) Cell 

 after plasmolysis has taken place. 



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 eon- 

 diiions. 



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

 tors that determine the tolerance of plants toward alkali are : 



^ Marchal, E., Influence des Sets mmiraux nvtntifs sur la FroducUon 

 des nodosiUs ehes le Fots; Compt. Rend. Acad. Sei. (Paris), Tome 133, 

 No. 24, p. 1032, 1901. 



