The Development and Significance of the Root Nodules of Casuarina

Abstract

Abstract Young plants of Casuarina cunninghamiana and of C. equisetifolia growing in water culture developed macroscopic nodules in 26 to 35 days from inoculation, the nodulation being most successful at pH near to neutrality and falling off much more rapidly at lower pH than in other non-legume nodule-forming genera, confirming the distinctiveness of the Casuarina organism. The roots springing from the nodule lobes are shown to be characterized by upward growth and in this to resemble remarkably closely the corresponding roots of Myrica. Nodulated plants of Casuarina are able to grow vigorously in culture solution free of combined nitrogen, showing that fixation of atmospheric nitrogen occurs, amounting in C. cunninghamiana to 50 mg. per plant during 6 months of active growth. The evidence indicates that the fixation occurs in the nodules, and that these have exactly the same functional significance as those of legumes.