Why Do the Roots of Leguminous Plants Have Swellings?

If you pull a bean plant from the earth, you can see many round swellings oil the roots. In fact all the roots of leguminous plants, such as broad bean, pea and peanut plants, have such swellings. If you squeeze one, a purple-red liquid comes out. The swelling is called a root nodule and it contains countless ;iodine bacteria. The bacteria catch nitrogen plants to produce and the plants provide the bacteria with moisture and nutrients for their existance. Thus the plants and bacteria each other for life.