THE CHEMISTRY OF THE FARM. 



COMPOSITION OF A CROP OF MEADOW GRASS. 



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. 



Punction of the Leaves. — The source of vegetable 

 carbon is the carbonic acid gas present in the atmosphere. 

 Carbonic acid gas passes more readily through the cuticle 

 of a plant than do the nitrogen and oxygen which make 

 up the bulk of the atmosphere. The carbonic acid thus 

 absorbed is decomposed within the chlorophyll cells of the 

 plant under the influence of light, oxygen being evolved, 

 and the carbon retained by the plant. All green parts of a 

 plant probably share in this action, but it is pre-eminently 



