02 



ELEMENTS OF AGRICULTURE 



the air and the soil (page 116). However, the ultimate 

 source of all nitrogen is from the air. The nitrogen of the 

 soil was obtained from the air (page 116). 



68. Water, Dry Matter and Ash. If a plant is heated 

 for some time at a temperature a little above boiling, 

 the water is driven off. By weighing before and after 

 drying, the percentages of water and of dry matter are 

 determined. When the dry matter is heated very hot, a 

 part of it burns and leaves ash. The ash contains all the 

 potassium, magnesium, calcium, iron, phosphorus, chlorin, 

 sodium and silicon of the plant, and some of the sulfur. 

 The ash, therefore, contains all the material that came 



from the soil, except part of the 

 sulfur, and the nitrogen. 



69. Relative Amounts of the 

 Different Elements in Plants. 

 Oxygen and hydrogen, chemi- 

 cally united in the form of 

 water, make up the largest part 

 of all growing plants. Turnips, 

 beets and pumpkins are about 

 nine-tenths water. They contain 

 a larger percentage of water than does milk. The per- 

 centage of water is much less in hay or grain, but few 

 plant products contain less than 10 per cent of water, 

 even when air-dry. 



Hydrogen and oxygen aisr also contained in other 

 compounds of the plant. In these compounds they make 

 up about 40 per cent of the dry matter. ' 



Carbon is next in importance. About half of the dry 

 matter is carbon. 



Fio. 37. Composition of the 

 potato: 1, Water; 2, compounds 

 of carbon, hydrogen and oxygen, 

 chiefly starch; 3, nitrogen; 4, all 

 other elements 



