The occurrence of nitrogen-fixing root nodules on non-leguminous plants

At present it is known that some 13 genera of non-leguminous Angiosperms include at least some species which bear root nodules with the property of nitrogen fixation.Alnus is the best known example. To assist in the assessment of the ecological importance of these plants, the author has surveyed the relevant literature to discover how many species in each of the genera have been recorded to bear noduleS. He also provides evidence of this feature in several species not hitherto reported. Of an estimated total complement of 342 species in the 13 genera, 118 species haye so far been recorded to bear nodules. The remaining species do not appear to have been examined for the presence of nodules.