Legumes are plant species that can fix atmospheric nitrogen, and thus legumes do not need costly and polluting fertilisers. Such an advantage is provided by special bacteria that live in small, round homes, named nodules, which are built by the plant in the roots. Basically, plants provide the home and food for bacteria, and, in return the bacteria transform atmospheric nitrogen into plant-edible nitrogen. Plant physiologists Voisin et al. study hypernodulating legumes, that are plants that have more homes to host bacteria, to design new species needing less fertilisers.