40 CHAPTER III 



Harmful Effects of Brak Salts.— The injury to crop 

 production due to the presence of brak salts in the soil is partly 

 direct, due to their harmful effect on the plant and germinating 

 seed, and partly indirect, due to their effect upon the soil and 

 its micro-organic flora. 



Summarised briefly, the following are the most important 

 points : — 



A. Jnjury to Plants.— (1) Plasmolysis of Plant Cells. — 

 The high concentration of salts in the soil solution retards the 

 rate of water absorption and therefore also retards general de- 

 velopment. In extreme cases where the soil solution is more 

 concentrated than the cell sap of the root hairs, the movement 

 is reversed, water passing from the root hairs into the soil solu- 

 tion. This results in plasmolysis of the plant cells followed 

 shortly by the death of the plant. 



(2) Gemiination of Seeds. — If the soil solution is concen- 

 trated enough, water absorption may be entirely prevented, 

 and the seed, therefore, fail to germinate. In this case it 

 merely lies dormant in the soil. In less extreme cases the 

 water absorption is retarded and, therefore, germination is 

 delayed. In such cases the seed may take three or four times 

 the normal time to germinate. 



(3) Structure of Plant. — The presence of considerable 

 quantities of soluble salts appears to affect the structure of 

 plants. Harter, working with cereals found a very noticeable 

 thickening of the cuticle and outer walls of the epidermal cells 

 occurred, and a conspicuous bloom or waxy deposit formed on 

 the surface of the leaves. 



(4) Corrosion of Surface. — Particularly noticeable in the 

 case of trees which have become well-established, and later 

 subjected to a gradual accumulation of soluble salts at the sur- 

 face. The effect is to corrode the plant at the base of the 

 stem or trunk, i.e., at the root-crown. The bark at this point 

 becomes dark in colour and crumbles away readily. The 

 corrosion may go deeper and partly or completely prevent the 

 upward passage of food from the roots to the upper parts of 

 the plant. This effect is most marked in the case of the car- 

 bonates of sodium and potassium. 



(5) Direct Toxicity. — It is possible that certain brak salts 

 exert a direct toxic effect on the plant, but to what extent this 

 is a factor in the general injury to the plant is not know^n. 

 Some of the salts are extremely toxic when alone in far 

 lower concentrations than frequently occur in soils with little 



