Answer: Legumes.
Step-by-step explanation: Nitrogen fixation in legumes starts from the formation of nodules. The bacteria in the soil invades the root and multiply in number.
The nutrients and the energy required the bacteria is provided for the proper growth of bacterial cell.
The legumes starts to germinate and the nodules turns from grey to pink. The pink color indicates that oxygen is flowing to the bacteria.This is how plants encourage the growth of nitrogen fixing bacteria in legumes.