Symbiotic stars have sometimes been misidentified as planetary nebulae, because their line spectra are similar to those of planetary nebulae particularly in the ultraviolet L.(Houziaux 1982 in “The Nature of Symbiotic Stars”, M. Friedjung & R. Viotti eds., Reidel. p 229), while the infrared shows the presence of the spectrum of a cool star. The similarity is not complete; when H. E. Schwarz (1988 in “The Symbiotic Phenomenon”, J. Mikolajewska et al eds., Kluwer, p 123) plotted a graph of two ratios derived from emission line fluxes, symbiotic stars did not occupy the regions of the diagram occupied by planetary nebulae and H II regions.