Abstract
The effect of the presence of hydrogen and of carbon monoxide on the fixation of nitrogen in detached root nodules of non-legumes has been studied, fixation being measured by the use of 15N. Parallel tests on legumes (pea and soya bean) have been included. Fixation in the nodules of Casuarina, Alnus, and Myrica is inhibited in the presence of substantial proportions of hydrogen, to a degree resembling that shown in legumes. Fixation in Alnus and Myrica is arrested in the presence of small proportions of carbon monoxide, and here again the sensitiveness is of the same order as in legumes.