A method of distinguishing between a flavone and a flavonol and characterising the latter is described. It consists in subjecting the ketonic fission product of the fully methylated anthoxanthin, representing the condensed benzene nucleus to the action of 40% aqueous hydrobromic acid, ω-Methoxy-ketones derived from flavonols yield coumaranones which could be converted into benzylidene derivatives. Simpler examples and more difficult cases such as gossypetol-tetramethyl-ether and calycopteretol pentamethyl-ether have been used for the investigation. The nature of the products has been proved by independent synthesis. The ketone obtained by the fission of methyl gardenin undergoes this reaction and hence supports the constitution of gardenin as a flavonol. Ortho-hydroxy-ketones which are unsubstituted in the ω-position do not yield any crystallisable product in this reaction.