36 NATURE OF ALKALI INJURY TO THE PLANT 



cells. This movement is necessary to the normal, function- 

 ing of plants. An ordinary plant, such as wheat, absorbs 

 and transpires several times its own weight of water each 

 day. Should this movement be reduced, the growth of 

 the plant is retarded. If it is entirely shut off the plant 

 dies, as pointed out by Pfeffer (12). 



The exact action that takes place when a plant cell comes 

 in contact with a solution more concentrated than its own 

 content was long ago pointed out by deVries (15) and 

 Pfeffer (n). Water passes out of the cell and the plasma 

 membrane draws away from the cell-wall leaving the cell 

 in a plasmolyzed condition. The rapidity of plasmolysis 

 depends on the relative concentration of the solution 

 inside and outside of the cell. So well known is this 

 phenomenon that the method is used constantly in de- 

 termining the concentration of the cell-sap under various 

 conditions. 



The above conception helps to explain the observed 

 action of plants. The soil solution of land high in alkali is 

 stronger than the cell-sap; therefore, no plant growth 

 takes place. In other land where there is less alkali, the 

 concentration may be just strong enough to reduce the 

 rate of water absorption but not enough to shut it off 

 entirely. Under this condition the crop yield would be 

 reduced. Thus, every gradation from a normal crop to 

 no crop at all may be found in a single field. 



Under some conditions, such as after irrigation or heavy 

 rains, alkali may be so diffused throughout the soil that the 

 concentration at any point is not sufficient to prevent the 

 crop from beginning a good growth. As the season ad- 

 vances, the salt may accumulate at the surface of the 

 soil until irrigation water is applied. It may then be 

 washed down to the roots in a concentrated form causing 



