The Composition and Use oe Fektilizeks. 19'U 



forms of burning, the oxygen of the air is simply uniting with 

 other elements. Thus, in a coal fire, the oxygen unites with the 

 carbon of the coal. The heat is produced by the union of the 

 two elements. 



(c) Relation to Fertilizers. — The oxygen which plants use 

 comes largely from the air, of which it constitutes about one- 

 fifth, and this amounts to about 10,000 tons an acre. Some of, 

 the oxygen that plants use for tissue formation and elaboration 

 of plant compounds is supplied in the form of water, which is 

 a compound of oxygen and hydrogen. 



Water {Hydrogen and Oxygen). — Growing plants consume a 

 larger amount of water than of any other compound. More or less 

 water is separated within the plant into its constituent element?, 

 hydrogen and oxygen, and these are then built into the tissues and 

 compounds which it is the office of the plant to elaborate. In this 

 manner, water acts as a direct fertilizer. The water is supplied 

 to the soil by rains, and from the soil it is taken into the plant 

 through the delicate root-hairs. Most of the water that enters a 

 plant through the roots is evaporated finally from the leaves into 

 the air as water vapor, this process being known as transpiration. 

 The amount of water transpired into the air is immensely greater 

 than that retained in a plant. Some plants exhale their own 

 weight of water during 24 hours in hot, dry weather. A 

 crop of barley grown on an acre of land may weigh 5,000 

 pounds, grain and straw included. Of this there will be 500 

 pounds of water and 4,500 pounds of dry or solid matter, to 

 produce which the crop has evaporated from the growing plants 

 during their period of growth not less than 700 tons of water, 

 an amount of water which would require a railway train of 

 35 cars to carry. Under average conditions, 300 pounds of water 

 will have to pass through a plant into the air, while one pound of 

 solid matter is bring added to the plant. The need for enormous 

 quantities of water in growing crops is obvious, but, im. regions 

 adapted to agriculture, plants usually receive from rain all the 

 water (oxygen and hydrogen) needed. Hence, these plant food 

 elements do not usually enter into a farmer's consideration, when 

 he is planning to supply his crop with needed plant food. How- 

 ever, it is essential that the losses of water from the soil shall be 

 controlled, as can be done by proper means of tillage, keeping 

 up supply of humus, etc. When water is suppli d to plants by 

 irrigation, it is very properly regarded as a fertilizer, and an 

 extremely important one. 



