The experimental data are analysed with the following conclusions. The molecular decay time τ0 of a thin anthracene crystal lamina at room temperature is 10 nsec. The thick crystal values are increased by self-absorption to 31.6 nsec (volume excitation, e.g. by γ-rays), 24.1 nsec (surface excitation, e.g. by ultra-violet or α-rays, and emission observed by transmission) and 19.4 nsec (surface excitation, and observation by reflection). Surface oxidation or reduction in crystal thickness yields lower values. For microcrystals of dimensions comparable with the exciton mean free path (similar 0.1 γ), the decay time is reduced below τ0 due to premature conversion of excitons into photons at the crystal surface.