1G2 WALL'S MANUAL 



In the case of all plants, the following operations 

 are going on at the same time: The leaves are 

 absorbing carbonic acid from the air, and the roots 

 are drinking in water from the soil. There is a 

 constant tendency to supply the deficiency of water 

 in the root, and keep it constantly charged with as 

 much as it can dissolve of the plant food. 



Under the influence of daylight the carbonic acid 

 is decomposed, its oxygen returned to the air, and its 

 carbon, retained in the plant. 



Water taken in by the [roots circulates through 

 the sap vessels of the plant, and is drawn toward the 

 leaves, where it is evaporated. This water contains 

 the nitrogen and mineral food required by the plant, 

 and some carbonic acid, while the water itself consists 

 of hydrogen and oxygen. Thus we see plants obtain 

 their food in the following manner : 



Carbon, in the form of carbonic acid, from the 

 atmosphere, and from that contained in the sap, the 

 oxygen being returned to the air. 



Oxygen and hydrogen, from the elements of the 

 water constituting sap. 



Nitrogen, from the soil, chiefly in the form of 

 ammonia. It is carried into the plant through the 

 roots, in solution in water. 



Mineral elements, from the soil, and only in solution 

 in water. 



The food taken up by the plant undergoes such 

 changes as are required for its growth ; the nutritive 

 portions of the sap are resolved into wood, bark, 

 grain or other necessary parts. 



The results of these changes are of the greatest 

 importance in agriculture, and no person ought to be 



