Key to the species of genus Rhizobiuni. I. Litmus milk alkaline. A. Forms a serum zone in milk. Young cells peritrichous. 1. Causes formation of root nodules on species of the genera Lathyrus, Pisum, Vicia and Lens. Bacteroids irregular with x-, y-, star- and club-shaped forms. 1. Rhizohium leguminosarum. 2. Causes formation of root nodules on Phaseolus vulgaris, P. muUiflorvs and P. angustifolius . Bacteroids, vacuolated rods, few branched forms. 2. Rhizohium phaseoli. 3. Causes formation of nodules on species in the genus Tri folium. Bacteroids pear- shaped, swollen, vacuolated. Pentoses usually not fermented. 3. Rhizohitim trifolii. B. No serum zone formed in milk. Monotrichous cells usually occur; in some cases all motile cells are monotrichous. 1. Causes formation of nodules on species of the genus Lupinus and on Ornithopus sativus. Bacteroids vacuolated, rods seldom branched. 4. Rhizohium lupini. 2. Causes formation of nodules on Soja max. Bacteroids long, slender rods, seldom vacuolated or branched. 5. Rhizohium japonicum.* II. Litmus milk acid. Forms a serum zone in milk. Causes formation of root nodules on spe- cies of the genera Melilotus, Medicago and Trigonella. Bacteroids club-shaped, branched. Young cells peritrichous. 6. Rhizohium meliloti. 1. Rhizohium leguminosarum Frank, Slight acid production from glucose, ga- 1890, emend. Baldwin and Fred, 1929. lactose, mannose, lactose and maltose. (Frank, Landwirtschaftliche Jahrbiicher, Aerobic. 79, 1890, 563; Baldwin and Fred, Jour. Bact., Optimum temperature, 25° C. 17, 1929, 146.) Source: Isolated from root nodules on le.gu.mi.no.sa'rum. M.L. fern. pi. n. Le- Lathyrus, Pisum (pea), Vicia (vetch) and guminosae old family name of the legumes; Lens (lentil). M.L. fern. pi. gen. n. leguminosarum of leg- Habitat: Widely distributed in soils where umes. the above-mentioned legumes are grown. Rods, 0.5 to 0.9 by 1.2 to 3.0 microns. Mo- tile by means of peritrichous flagella. Bac- 2. Rhizohium phaseoli Dangeard, 1926. teroids commonly irregular with x-, y-, (Le Botaniste, S^r. 16, 1926, 197.) star- and club-shaped forms. Vacuolate pha.se'o.li. Gr. noun phaselus the kidney forms predominate. Gram-negative. bean; L. noun phaseolus the kidney bean; Growth on mannitol agar is rapid, with M.L. mas.n. Phaseolus generic name of the tendency to spread. Streak is raised, glis- bean; M.L. gen . noun phaseoli of Phaseolus. tening, semi-translucent, white, slimy and Rods. Motile by means of peritrichous occasionally viscous. Considerable gum is flagella. Bacteroids are usually rod-shaped, formed. often vacuolated with few branched forms.
- No specific name has been proposed for the organism causing the formation of nodules
on plants that are members of the so-called "cowpea" group. Data showing possible inter- relationships of certain plant species of the soybean and cowpea cross-inoculation groups prompted Walker and Brown (Soil Science, 89, 1935, 221-225) to propose a consolidation of the two groups to be recognized as being inoculated by a single species, Rhizohium ja- ponicum. Results obtained by Reid and Baldwin (Proc. Soil Sci. Soc. Amer. for 1936, 1, 1937, 219) show these inter-relationships to include the lupine group also.
