Observational data of the Evershed effect are used to examine the validity of the models to account for the origin of the filamentary structure of the penumbra. The rolling convection model of Danielson (1961) and the elevated dark filament model of Moore (1981) and Cram et al. (1981) are considered. The dependence of the Evershed velocity on the equivalent width at the outer edge of the penumbra is compared with that in the inner penumbra. Also, the dependence of the Evershed velocity on the lower level excitation potential of spectral lines is studied. The results show that the elevated dark filament model produces a better agreement with the observational data than to rolling convection model.