Three principal beryllium-morin complexes, a (1 + 1) monomer, a (1 + 1) dimer, and a (1 + 2) complex are found and conditional equilibrium constants for their formation are evaluated. Approximate ionization constants, absorption spectra, and the relative fluorescence intensities for five ionic species of morin are also determined in a spectrophotometric and fluorometric study of morin. The following interrelationships are discussed: pH, ionization of morin, absorption spectra of the various ionic species of morin and of the berylliummorin complexes, equilibria for the reactions between beryllium and morin, the period of time between preparation of the solution and measurement of the fluorescence, and fluorescence intensity.