Abstract
N fixation exps. indicated that certain strains of nodule bacteria from the cowpea group of hosts are superior to other strains from the same group. Results from immunological tests indicated that a close protein kinship exists among Crotalaria spp. and the cowpea plant, but not between these spp. and alsike clover and field peas. Complement fixation and agglutination compared favorably with each other as means of identifying legume-nodule bacteria. Because of its simplicity the agglutination reaction is to be preferred. Group agglutination may probably be due to the presence in a given leguminous sp. of an enzyme specific for certain Rhizobium spp. and not for others.