The Structure of Ineffective Root Nodules of Legumes: An Unusual New Type of Ineffectiveness, and an Appraisal of Present Knowledge

A new type of symbiotic ineffectiveness in subterranean clover is described in which very slow-growing nodules are produced. In these the nodule bacteria are not released from the infection threads, where they multiply at the expense of the host tissue. Comparison of nuclear size of normal effective nodules with that of these ineffective nodules suggests that the nodule tissue is almost devoid of the disomatic cells in which the nitrogen-fixing bacteroid form of Rhizobium normally develops. The bacterial strains giving rise to these nodules were obtained as stable variants of a strain producing structurally and cytologically normal nodules.