The present paper is a criticism of the application of the monoatomic layer and simple dipote theory to thermionic emission. We have come to the following conclusions: (1) the existence of the monoatomic layer is conditional, it depends upon the temperature, surface structure and purity of the substrate as well as upon the vacuum environment; (2) the appearance, and sometimes disappearance, of the emission peaks is a problem for further study, and it can not be explained simply by the monoatomic layer and dipole theory; (3) the enhanced emission after adsorption of foreign atoms or molecules is not due to the formation of dipoles which lower the work function of the substrate, but comes from the valence electrons of the adsorbate, and (4) the "L" cathode is a Ba-O-W system, neither monoatomic nor monomolecular, and the dipole theory is not applicable here.