Microbes

We saw that there are very many microbes in the soil.
Some microbes change organic matter into humus.
Other microbes bring nitrogen to plants.
We know that leaves get carbon from the air (see Booklet No. 2, page 21).
There is also nitrogen in the air. To grow, plants need nitrogen. But leaves cannot take nitrogen from the air.
In the soil there are microbes that can take the nitrogen in the air for their own food.
When these microbes die, they remain in the soil and decompose.
The microbes' nitrogen is changed into mineral salts.
The roots of plants can absorb these mineral salts through their root hairs (see Booklet No. 1).
Everywhere in the soil there are microbes that Can take in nitrogen.
Some of them gather on plant roots where they form little beads, or nodules.
The microbes in these little beads bring nitrogen to the plants.
Not all plants have these little beads.
They are found only on plants of the legume family.
Groundnuts, Dolichos bean, Crotalaria, beans, peas, Stylosanthes are all legumes.

Groundnut plant