56 WILSON & TOOMKK FERTILIZER COMPANY 



Chapter X 



Plant Constituents 



Plants of all kinds, whether garden vegetables or fruit 

 trees,. are alike in their constituents and mode of growth. 

 Though other elements are shown by chemical analyses, 

 the essentials for plant growth have been found to be 

 oxygen, hydrogen, nitrogen, carbon, phosphorus, sulphur, 

 potassium, calcium, iron, and magnesium; or, as Brooks 

 puts it : -"Air to breathe and water to drink ; four acids, 

 carbonic, nitric, phosphoric, and sulphuric; and four 

 bases, potash, lime, iron, and magnesia." 



Air 



Oxygen The plant uses oxygen in two forms: Com- 

 bined oxygen which enters the plant through the roots in 

 connection \vith other elements which are used in the 

 form of oxides and the free oxygen of the air. This latter 

 is absorbed by all living plant surfaces, but more abun- 

 dantly by leaves and tender growing parts. Free oxygen 

 in the soil is essential to plant life (except swamp vegeta- 

 tion) : Germinating seeds require an abundance and 

 when roots are deprived of air the plants soon suffocate 

 and die. The absorption of oxygen is accompanied by a 

 giving off of carbonic acid gas a product of the breaking 

 down of living matter worn out by the "energy of grow- 

 ing" and of parts going to decay, as in injured tissues or 

 faded flowers. This process is called "respiration." 



