Friedman, S. (State University, Ghent, Belgium), and J. De Ley. "Genetic species" concept in Xanthomonas. J. Bacteriol. 89:95-100. 1965.-Deuterated, N(15)-labeled deoxyribonucleic acid (DNA) from Xanthomonas pelargonii forms distinct hybrids with ordinary DNA from X. hederae, X. juglandis, and X. carotae. Hybridization is less pronounced with X. phaseoli and X. begoniae. There is evidence that some hybridization occurs with X. vesicatoria, X. campestris, and X. tamarindi. These results favor the concept of a "genetic species," rather than a division of the genus into many separate species based almost entirely on phytopathogenic host specificity.