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SCIENCE PROGRESS 



of nitrate and should therefore be reckoned among the acids. 

 On summing the constituents with nitrogen included, and setting 

 off equivalents of the acids against the bases, it is almost always 

 found that the acids are in excess in the plant. This means 

 that during nutrition in a neutral solution of calcium nitrate, 

 such as naturally prevails in the soil, the plant withdraws an 

 excess of nitric acid over lime. Presuming the solution to be 

 ionised, the nitric acid ions continue to pass into the plant by 

 osmosis to a greater extent than the calcium ions, because the 

 former are more rapidly withdrawn from solution and utilised 

 by the protoplasm. But if an excess of acid enters the plant, an 

 excess of base must be left behind, and the net action of the plant 

 on the medium in which it is growing will be the production 

 of an alkaline rather than an acid reaction. There might still, 

 however, be a secretion of an organic acid, equivalent to or 

 even in excess of the bases unabsorbed. 



This, however, does not prove to be the case on experiment; 

 plants grown in water cultures of neutral or even slightly acid 

 reaction at starting induce a gradually increasing alkalinity, 

 eventually to the destruction of growth, unless the solution 

 be changed or the alkalinity neutralised. An example {Proc. 

 Roy. Soc. 1905, B 77, 1) may be given of wheat grown from 

 seed to seed in a water culture the liquid of which was never 

 changed, though its reaction became in the end faintly alkaline, 

 instead of the distinct acid with which it started. 



Distribution of Acids and Bases after growth of Wheat in 

 Water Culture. 937 Grains of Dry Matter produced. 



1 Represents nitrogen in the seed, dust, etc. 



