FOOD FOR PLANTS 65 
These combinations are called nitrates. Nitrates 
can be bought to use for fertilizer, but they are 
expensive. There is only one kind of plant that 
can use nitrogen from the air, and it is a family 
of bacteria that live on clover roots. When a 
full grown clover plant is pulled up, roots and 
all, many little lumps can be seen clinging to the 
roots. These lumps are full of bacteria, so small 
that a microscope is needed to see them at all. 
This one kind of bacteria can take nitrogen 
from the air and combine it with other elements 
from the soil to form nitrates. They leave these 
nitrates in the earth, and after the clover crop 
is cut down, the nitrates remain there for other 
plants to use. These bacteria only live on the 
roots of clover or the roots of other plants of 
the clover family. 
If grass is not growing well, it is a good idea 
to plant clover. One planting of clover will 
enrich the soil enough to last for several seasons. 
Other members of the same family that are 
good for the soil are peas, beans, and alfalfa. 
Wherever these plants have been growing, the 
