200 Bureau of Farmers' Institutes. 



(d) Specific Functions in Plant Growth. — Oxygen, next to 

 carbon, is the most abundant element found in plants, and there 

 are very few compounds occurring in plants which do not con- 

 tain more or less oxygen. The chief function of oxygen is to 

 supply the various compounds of plants with the needed portion 

 of this material. Plants require oxygen about as much as do 

 animals. Green plants cannot flourish without a supply of oxy- 

 gen. The absence of oxygen prevents the germination of seeds. 

 Considerable quantities of oxygen are absorbed from the air by 

 the opening buds of trees. More or less oxygen in the soil is 

 necessary for the active life of roots. In the act of flowering, 

 the absorption and chemical action of oxygen in the blossom 

 is so marked, in some cases, as to develop sufficient heat to be 

 measured by a thermometer. 



Water (Hydrogen and Oxygen). — In the combination of oxy- 

 gen with hydrogen in the form of water, these two elements per- 

 form important functions. In the first place, nearly all the hydro- 

 gen found in the different compounds of plants comes from water. 

 More or less of the oxygen is also supplied this way. In addition 

 to furnishing materials with which to build other compounds, 

 water acts as a carrier within the plant in transferring from one 

 part of the plant to another, as needed, the various products con- 

 tained in the plant, just as the blood in the animal body carries 

 to every portion the nutriment adapted to each organ and part. 



Nitrogen. 



(a) Source. — Nitrogen occurs in nature in the following 

 forms : 



(1) As a constituent of air. 



(2) In the form of ammonia. 



(3) In the form of nitric acid and nitrates. 



(4) In various other forms in plants and animals. 



(1) Nitrogen in Air. — Nitrogen, uncoinbined with other ele- 

 ments, forms about four-fifths of the air. Since the nitrogen in 

 the air is not combined, we cnn perceive its properties for our- 

 selves, and our observation shows us that it is a gas, which has 

 neither color, taste nor smell. 



(2) Nitrogen in Ammonia. — Nitrogen combined with the 

 element hydrogen forms ammonia. Ammonia is present in the 

 air in very small quantities. Ammonia is formed when vegetable 

 and animal substances containing nitrogen decompose. 



