Abstract Sugar maple seeds were soaked in water or exposed to water vapor under aerobic or anaerobic conditions and subsequently germinated. In general, the anaerobic treatments stimulated germination. The effects of seed covering structures on the diffusion of leachable materials out of sugar maple seeds was also tested. Immersion in water and exposure to water vapor both stimulated germination. This enhancement was attributed to the quasi-anaerobic conditions during imbibition and the leaching of inhibitors. Forest Sci. 25:307-311.