INOCULATION AND NITROGEN. 225 



large part is carbon; carbon is taken from the air 

 by the leaves of the plant. There is plenty of car- 

 bon always for plant growth. There is usually 

 plenty of water. Mineral elements — potash, phos- 

 phorus, lime, iron and so on — are easily enough 

 added to the soil. The sole remaining element is 

 nitrogen. Nitrogen is one of the essential elements 

 in the proteins of food, the albumens. Nitrogen is 

 essential to nearly all life, animal and plant. All the 

 higher animals need much nitrogen in their foods. 

 All the grains have in them much nitrogen. Nearly 

 all crops taken away from the soil remove a great 

 deal of nitrogen. Soil waters leach it away. Since 

 the beginning of the world everything has preyed 

 upon the nitrogen of the soil. The rocks in the be- 

 ginning held little or none of it. Whence did the 

 soils then obtain their nitrogen supply! 



Ttco Classes of Plants. — There are two classes, 

 very broadly speaking, of plants in the world, the 

 nitrogen gatherers and the nitrogen users.. Corn, 

 wheat, the grasses, potatoes, flax, oats, nearly all 

 farm crops use nitrogen and can not get it except 

 as it is already stored for them in the soil. That 

 at least is as far as we know now. At any rate 

 soils grow poor in nitrogen when crops of corn, 

 w'heat, hay or almost any crop except clover or some 

 other legume is grown upon it. Certain crops are 

 soil builders. Certain other crops are soil robbers. 

 The legumes are the soil builders. They get nitrogen 

 in some way. How do they do this? 



Abundant Nitrogen in Air. — Nitrogen exists in 



