Colwell, R. R. (University of Washington, Seattle) and J. Liston. Taxonomic analysis with the electronic computer of some Xanthomonas and Pseudomonas species. J. Bacteriol. 82:913-919. 1961.-Forty organisms, including 16 Xanthomonas spp., 5 strains of Pseudomonas solanacearum, 4 strains of P. aeruginosa, 6 strains of P. fluorescens, 5 freshly isolated strains of pseudomonads, as well as the American Type Culture Collection strains of Flavobacterium aquatile, Vibrio cuneatus, Vibrio metschnikovii, and Aeromonas formicans, were extensively tested morphologically, physiologically, and biochemically. The Adansonian principle of classification was employed in an analysis, made with an electronic computer, of the characteristics of these cultures. The results showed that Xanthomonas spp., Pseudomonas spp., and P. solanacearum were clearly distinct at the genus level. Xanthomonas could be divided into two subgroups; within the subgroups, a number of species appeared to be virtually synonymous, indicating overspeciation. The fluorescent pseudomonads fell into three overlapping groups, mesophilic P. aeruginosa, psychrophilic P. aeruginosa-like organisms, and P. fluorescens. A simplified table of physiological reactions is presented for the differentiation of the groups obtained.