Influence of the Numbers of Rhizobium supplied on the Subsequent Nodulation of the Legume Host Plant

The effect of numbers of Rhizobium supplied on the subsequentnumbers of nodules formed was tested with Phaseolus radiatusvar. aurea in water culture. Nine weeks after inoculation plants supplied with from 88,700to 887,000 bacteria per c.c. of culture solution bore significantlymore nodules than those given from 89 to 887 per c.c. An inoculumof 44,350 per c.c. produced intermediate numbers of nodules. One week after inoculation, the percentage of curled and ofinfected root-hairs on the seedlings was roughly proportionalto the logarithm of the bacterial numbers supplied, while thenumbers of nodules produced at this stage already showed a significantdifference between extreme doses of inoculum. Nine weeks after inoculation the final nodule numbers were relatedto the percentages of curled and of infected root-hairs afterone week. The final nodule numbers are related to the growth of the rootsystem since the final number of nodules per gramme of rootis independent of the initial dose of inoculum, the effect ofwhich was mainly to cause an increase in root growth.