THE CHEMISTRY OP THE FARM. 



COMPOSITION OF A CROP OF MEADOW GRASS. 



Total crop 



11,200 Ibs. 



Plants obtain the elements of which they are built up 

 partly from the soil, and partly from the atmosphere. 

 From the soil they obtain, by means of their roots, all 

 their ash constituents, all their sulphur, and nearly the 

 whole of their nitrogen and water. From the atmosphere 

 they obtain, through the instrumentality of their leaves, 

 the whole, or nearly the whole, of their carbon, with pro- 

 bably small quantities of nitrogen and water. 



Function of the Leaves. 1. Assimilation. The 

 source of vegetable carbon is the carbonic acid gas 

 present in the atmosphere. Carbonic acid and the other 

 gases of the atmosphere pass through the cuticle of the 

 plant, and are dissolved by the cell sap : carbonic acid 

 is much more soluble in water than the nitrogen and 

 oxygen which make up the bulk of the atmosphere. 

 The dissolved carbonic acid is decomposed within the 

 chlorophyll cells of the plant under the influence of 

 light, oxygen being evolved, and the carbon retained 



