PHYSIOLOGY OF COMN PLANT 



43 



--.■-'i ASH FROM SOIL 1% GREEN WTf :.;.? 



Fig. 17. — The source of elements supplying a maize plant. About 10 

 per cent of the green weight (50 per cent of dry weight) is carbon. 

 About 5 per cent is oxygen and 4 per cent hydrogen. The oxygen is 

 derived from the air in combination with carbon, from water or from 

 oxide salts. The hydrogen comes principally from water. Ash from 

 the soil equals about 1 per cent, and nitrogen J per cent of the green 

 weight. About 80 per cent of the green weight is water, not in com- 

 position. 



