ADJUSTMENT TO WATER 47 



60. Influence of soluble salts. The composition and density 

 of the cell sap naturally varies in different plants. In all ordi- 

 nary habitats the density is greater than that of the soil water, 

 since this is one of the necessary conditions of endosmose. The 

 density of the water content is determined by the amount of soluble 

 salts present in the soil, and by the amount of water applied to it. 

 The water content of ordinary soils contains from 0.01% to 0.1% 

 of dissolved salts. In alkaline lands the soluble salts vary from 

 0.2% to more than 3%. Up to 0.2%, the action of such salts 

 is not injurious, as indicated by the growth of ordinary field crops 

 upon them. Beyond this point concentration becomes more 

 and more injurious, owing to the difficulty of absorption. The 

 limit for the most resistant cultivated plants is reached at about 

 1%, and beyond this only such alkaline plants as the salt bush 

 and the greasewood are able to grow. Soils containing much 

 sodium carbonate and bicarbonate (black alkali) render osmosis 

 and absorption much more difficult. The injurious effects of 

 such salts become evident at a concentration of 0.05%, while only 

 the more resistant plants can withstand 0.1% to 0.2%. 



Experiment 9. Demonstration of osmosis. Tie a piece of parchment 

 or dialyzer paper over the bulb of a thistle tube, taking pains to make 

 it fit tightly. Fill the bulb with a 25% or 30% solution of common 

 salt and allow the latter to rise a short distance in the tube. Place 

 the bulb in a beaker filled with distilled water and support it by means 

 of a ring-stand. Follow the rise or fall of the column in the tube, and 

 mark the various heights. Test the distilled water from time to time 

 by means of a drop of silver chloride to determine whether the salt 

 has passed into it. When the column has reached the highest 

 point, place the bulb in a concentrated salt solution, and note the 

 behavior. 



Experiment 10. The effect of soluble salts. CJernnnate sunflower 

 seeds in three pots filled with sawdust, and after the seedlings are well 

 established, water one with distilled water, the second with a nutrient 

 solution, and the third with a 5% solution of common salt. Compare 

 the behavior of the seedlings, and note also the effect of the solutions 

 upon the root-hairs. 



Treat a thread of pond scum with 1% solution of common salt 

 colored with methyl blue. Note the effect, and after a few minutes 

 replace the salt solution with distilled water. This shrinkage of the 

 protoplasm, which is known as plasmolysis, is essentially wliat orcurs 

 in the root-hairs in soil watered with the salt solution. 



