CHEMICAL PHENOMENA IN LIFE 



Distinctly the same effect is produced by the 

 action of salt solution. A flower stalk or leaf stalk 

 of fleshy consistence put into potassium nitrate 

 of about 2 per cent very soon becomes unelastic, 

 flexible, like a withered plant, and shortens its 

 length by some millimetres in a length of about 

 10 centimetres. We learn from this phenomenon 

 that the pressing of protoplasm against the cell- 

 wall is due to osmotic forces. Hugo De Vries 

 showed, in 1884, that it is possible to use the 

 suppression of osmotic pressure in cells or of the 

 Cell Turgor, as botanists say, by salt solution, 

 for the measurement of the osmotic pressure in 

 normal cells. The procedure is essentially identical 

 with the so-called plasmolysis we have spoken of 

 in a previous chapter. One has to apply solutions 

 of a pure mineral salt of different concentrations. 

 It is usual to take potassium nitrate because it is 

 easily available in quite pure preparations and 

 because the percentage in solutions is nearly 

 identical with the standard gauge in chemical 

 work, the Gramm Molecule Solution. Solution of 

 potassium nitrate containing 10-1 gr. in 100 gr. 

 water is only slightly more than 10 per cent con- 

 centration, and is a molecular solution, containing 

 one gramm molecule potassium nitrate, 101 gr. in 

 I litre of water. If we put sections of plant 

 tissue in different potassium nitrate solutions from 

 0-05 normal to 0-2 normal strength, we find that 

 the separating of the protoplasm from the walls 



