312 



THE PRINCIPLES OF SOIL MANAGEMENT 



might completely prevent the growth of useful crops 

 if the alkali were black. 



173. Effect of alkali on crops. The presence of rela- 

 tively large amounts of salts dissolved in water and 

 brought in contact with a plant cell has been shown by 

 DeVries to cause a shrinking of the protoplasmic lining 

 of the cell, the shrinking increasing with the concentration 



a 



b 



Fig. 103. Showing plasmolysis of plant cells produced by strong solutions 

 of salts, (a) Normal cells; (b) cell subjected to action of 5 per cent solution 

 of KN0 3 , showing (z) cell-wall, (p 1 , p 2 ) plasmatic membranes, (s) vacuole; 

 (c) cell subjected to action of 2.3 per cent solution of KNO3, causing a slight 

 contraction of the plasmatic membranes. 



of the solution. This causes the plant to wilt, cease 

 growth and finally die. The nature of the salt, and the 

 species and even the individuality of the plant, deter- 

 mine the point of concentration at which the plant 

 succumbs. 



174. Direct effect. The directly injurious effect of 

 the chlorides, sulfates, nitrates, etc., of the alkalies 

 and alkali earths is due to this action on the cell con- 

 tents. The carbonates of the alkalies have, in addition, 

 a corroding effect upon the plant tissues, dissolving the 

 portions of the plant with which they come in contact. 



