IT has been shown1–3 that fixation of atmospheric nitrogen is associated with nodule-bearing plants of alder (Alnus glutinosa), bog myrtle (Myrica gale) and sea buckthorn (Hippophae rhamnoides), enabling the plants to grow in a rooting medium free of combined nitrogen just as in the case of legumes. This is well illustrated by Fig. 1, which shows plants of sea buckthorn from a recent experiment. There are, of course, other non-legume root nodule plants, but those named, together with related species, are the examples occurring in northern countries.