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? 
Two 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, gats, 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, 
wheat, 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 
