50 THE PLANT. 



fully reconsider tlie various points with a ^ iew to lix- 

 iiig them permanently in the mind. 



Plants are composed of atmospheric and earthy 

 matter. 



Atmospheric matter is that which burns away in 

 the fire. Earthy matter is the ash left after burning. 



The organic matter of plants consists of three 

 gases, oxygen, hydrogen and nitrogen, and one solid 

 substance, carbon (or charcoal). The mineral parts 

 consist of potash, soda, lime, magnesia, sulphuric 

 acid, phosphoric acid, silicic acid, chlorine, oxide of 

 iron, and oxide of manganese. 



Plants obtain their atmospheric food as follows : — 

 Oxygen and hydrogen from water ; nitrogen from 

 some compound containing nitrogen (chiefly from 

 ammonia) ; and carbon from the atmosphere, where 

 it exists as carbonic acid — a gas. 



They obtain their earthy food from the soil. 



The water which supplies oxygen and hydrogen 

 to plants is readily obtained without the assistance 

 of manures. 



Ammonia is obtained from the atmosphere, by be- 

 ing absorbed by rain and carried into the soil, and it 

 enters plants through their roots. It may be artifi- 

 cially supplied in the form of animal manure with 

 advantage. 



Carbonic acid is absorbed from the atmosphere by 

 leaves, and decomposed in the green parts of plants 

 under the influence of daylight; the carbon is re- 

 tained, and the oxygen i* returned to the atmoa- 

 phere. 



