Introduction. 19 



ash, corresponding exactly to the ash left in the stove after a stick 

 of timber is burned. 



The constituents which form the dry matter of plants may be 

 divided into two classes the combustible and the non-combustible 

 part. The combustible part of plants is made up of six chemical 

 elements carbon, oxygen, hydrogen, nitrogen and sulphur, with 

 a small amount of phosphorus. Without these no plant will grow. 

 Carbon generally forms about one-half of the dry combustible 

 part of plants. Nitrogen seldom exceeds four per cent of the dry 

 matter and is generally present in much smaller amounts. Sul- 

 phur and phosphorus are still smaller in quantity. The re- 

 mainder is made up of oxygen and hydrogen. The carbon, hy- 

 drogen and oxygen form the cellulose, starch, lignin, gummy mat- 

 ters, sugars, fats and vegetable acids which plants contain. The 

 same elements united with sulphur and nitrogen form the very 

 important proteins, which are the life centers of the plant. When 

 all the above elements are united to phosphorus, we have addi- 

 tional important groups of plant compounds, called nucleins and 

 lecithins. 



Non-combustible part of plants. The non-combustible or ash 

 constituents form generally but a small part of the plant. A 

 fresh, mature corn plant will contain about 1.2 per cent of ash, 

 while the corn grain when dry, contains about 1.5 per cent. In 

 the straw of cereals the ash constitutes 4-7 per cent and cereal 

 grains 2-3 per cent of the dry matter. In hay 5-9 per cent will 

 be found. We find in leaves, especially old leaves, the greatest 

 proportion of ash. In the leaves of root crops the ash will amount 

 to 10-25 per cent of the dry matter. 



Essential elements. The non-combustible ash always contains 

 six elements potassium, magnesium, calcium, iron, phosphorus 

 and sulphur. It was once thought that these ash elements were 

 accidental, simply dissolved in the soil water and absorbed by the 

 plant and that they were not essential to its development. Liebig 

 proved that they were necessary; seeds were planted in pure 

 quartz sand contained in a series of pots to one of which nitrogen 



