18 EFFECT OF SOLUBLE SALTS UPON PLANTS. 



leaf surface and the accompanying thickening of the cuticle and 

 (2) increased concent rat ion of the cell sap. a 



The increased transpiration observed in wheat plants grown in 

 soils containing an amount of soluble salts too small to cause any 

 increase in the thickness of the cuticle or bring about any measurable 

 deposition of wax is probably to be regarded as a result of chemical 

 stimulation. It is well known that stimulation is effected by dilute 

 solutions of many substances which at greater concentrations are 

 toxic to plants. The writer'' found that magnesium chlorid, mag- 

 nesium sulphate, sodium sulphate, and sodium bicarbonate in water 

 cultures stimulated the growth of wheat seedlings when present in 

 dilutions too great to be toxic. Burgerstein, who has made a very 

 extensive study of the transpiration of plants under various condi- 

 tions, finds that maize plants when subjected to solutions of 0.02, 

 0.10, and 0.25 per cent potash (K 3 0) and soda (Na 2 0) for a period of 

 from one to four days exhibited a decreased transpiration as com- 

 pared with control plants growing in distilled water. On the other 

 hand maize plants grown during a period of forty-three to one hun- 

 dred hours in solutions of 0.1, 0.25, 0.5, and 1 per cent of calcium 

 nitrate and magnesium sulphate showed an increase of transpiration 

 in the two weaker concentrations but a decrease in the two stronger 

 concentrations. Burgerstein further finds that in very dilute solu- 

 tions (0.05 to 0.25 per cent) of magnesium, of ammonium sulphate, 

 and of calcium carbonate, transpiration as compared with that in 

 distilled water increases with the concentration of the solution until 

 a maximum is reached. 



SUMMARY. 



(1) Plants of wheat, oats, and barley grown from seeds in soils 

 containing 1, 1.5, and 2 per cent of total salts (0.7, 1.0, and 1.4 per 

 cent of sodium chlorid) very soon develop a pronounced waxy bloom 

 upon the leaf surface and a thickening of the cuticle. 



(2) The thickness o\' the cuticle increases with the concentration 

 of the soil solution. 



(3) The size of the epidermal cells decreases as the concentration 

 of the salt in the soil increases, the epidermal cells of the plants 

 grown in nonsaline soils being on an average the largest and those 

 in the soils containing the greatest concentration of salts being the 

 smallest. 



"Sachs (Ueber den Einfluss der chemischen und physikalischen Beschaffenheit 

 drs Bodens aui die Transpiration dor Pflanzen, Gressammelte Abhandlungen, 1: 417. 



L892 1 stairs thai transpiration from Leaves may be reduced by the presence of materials 

 dissolved in the water which the roots take up. 



& The Variability of Wheat Varieties in Resistance to Toxic Salts. Bulletin 79, 

 Bureau of Plant Industry, V. S. Dept. of Agriculture. L905, p. 42. 



c Die Transpiration der Pflanzen, Eine Physiologische Monographie. 1904. 



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