PLANT FOOD 



27 



not been proved essential, although in many cases plants 

 seem to do better with them than without them. The first 

 ten, however, are absolutely essential to the plant. 



14. Composition of the Plant.- About three-fourths of 

 the total weight of a green plant is water. The remaining 

 one-fourth of dry matter is manufactured by the plant and 

 is made up largely of fundamental organic substance con- 



DRY MATTER 

 25# 



Fig. 2. — Diagram showing the distribution of water and dry matter in 



plants. Drawing by E. DeTurk. 



taining only carbon, hydrogen, and oxygen. There is further 

 some organic substance which includes part of the nitrogen, 

 sulphur, and phosphorus. The remainder of the dry matter, 

 containing potassium, calcium, magnesium, iron, and some 

 of the nitrogen, sulphur, and phosphorus, in organic and 

 inorganic form, is necessary for the formation of funda- 

 mental substance, although not a part of it. 



Fig. 2 gives a graphic illustration of how water and dry 



