The evaluation of the purity and quality of nodule bacteria cultures, used for the inoculation of seeds, requires a useful morphological approach for control purposes. For that reason 23 sources of nodule bacteria were characterized with regard to their shape and form by means of living preparations. The typical stages of the nodule bacteria of various Leguminosae, appearing exclusively in the form of rods, were photomicrographed. These studies included bacteria isolated many years ago as well as those obtained in 1955. The inoculation material at hand consisted of slightly motile rods of straight and sometimes slightly bent form, the length of which differed even among nodule bacteria of the same species.In relation to the systematic classification of the Leguminosae, the nodule bacteria variations isolated from the former were united in the following 10 groups of forms:1. The forms from the Lupinus group as a morphologically homogeneous series.2. The nodule bacteria of Medicago sativa L., M. lupulina L., and Melilotus albus Med. with transitional characteristics between the individual species.3. The nodule bacteria of the Trifolium species, sometimes non-uniform, showed thick rods of variable lengths.4. The group of the nodule bacteria of Anthyllis vulneraria L., Lotus uliginosus L., and L. corniculalus L. characterized as short rods. A typical feature seems to be the development of star-shaped accumulations.5. The independent group of the nodule bacteria of Onobrychis sativa Lmk.6. The independent group of Ornithopus sativus Brot.7. The nodule bacteria of Vicia faba L. and V. sativa L. showing short and long rods with heavy mucus development.8. The nodule bacteria of Lens esculenta Moench showing short rods of varying thickness.9. The typical straight rods of Pisum sativum L. and P. arvense L.10. The long rods of Phaseolus vulgaris L. and P. nanus L. differing from those of Pisum sp. only by the slight bend of the rods and a typical development of star forms. The morphological differences we found appeared with such regularity in certain species that their occurrence was recorded in typical pictures.