HOW PLANTS FEED AND GROW 25 



25. Taking the plant apart. When a plant is analyzed 

 chemically it is found to consist of water, organic matter, and 

 ash. About 75 per cent of the average growing green plant is 

 water. A field of growing corn has been found to contain as 

 much as 80 per cent of water ; a potato crop, 79 per cent ; and 

 a cabbage patch, 9 1 per cent. Cured hay contains from 8 to 1 2 

 per cent of water, and corn in the crib, from 8 to 14 per cent. 

 Therefore, if a green corn plant is dried and weighed, there 

 may be left only 20 per cent of the original weight. The water 

 has been driven off by heat. When this dry material is burned 

 and weighed, only about I per cent of the original weight is left 

 as ash. The organic matter has been burned and has passed 

 off into the air in the form of gases, as in the case of the organic 

 matter of wood or coal burned in the stove or furnace. Thus, 

 the green corn plant is about 80 per cent water, 19 per cent 

 organic matter, and I per cent ash. 



Most of the organic matter of plants is carbon, which is 

 obtained from the air through the leaves. Nitrogen is a part 

 of the organic matter and came originally from the air. Only a 

 few plants are able to feed upon nitrogen in the free state in 

 which it exists in the air, and all of the agricultural plants except 

 the legumes, such as beans, peas, and clovers which are dis- 

 cussed later, take all their nitrogen from the soil, in which it 

 is combined with other elements. The water, the ash, and the 

 nitrogen, except the nitrogen which the legumes take from the 

 air, are obtained from the soil through the roots. 



26. Elements of plant food. Water is composed of hydrogen 

 and oxygen. Organic matter is composed of carbon, nitrogen, 

 and the same elements as water. The ash, or the mineral part of 

 plants, consists of phosphorus, potassium, calcium, iron, sulphur, 

 and magnesium, all of which are absolutely essential to the life 

 and growth of plants. To these must be added the equally indis- 

 pensable four elements coming from the air carbon, hydrogen, 

 oxygen, and nitrogen. Thus, there are at least ten elements 

 absolutely necessary for all plants. In the ash of nearly all plants 

 sodium, silicon, and chlorine are also found, and in many plants 



