Abstract Ovule development was studied in reciprocal crosses between Picea pungens Engelm. (blue spruce) and P. engelmannii Parry (Engelmann spruce). Reproductive failure was found to occur at several stages through the proembryo stage. Some pollen did not germinate; other pollen showed slight penetration of the nucellus before death occurred; and still other pollen brought about fertilization. Cessation of hybrid ovule growth occurred from the free nuclear stage through the egg stage. Irregularities within the archegonium before degeneration included the presence of large bodies, apparently protein, additional scattered chromatin-like material, and extra nuclei. Female gametophytes (prothallia) without archegonia contained proliferated and necrotic cells in the archegonial region. Necrosis of the female gametophyte occurred nine days after strobilus pollination in unpollinated ovules. Engelmann spruce × blue spruce ovules were similar to the reciprocal cross except when the female gametophyte grew into a group of few but very large cells and when greatly shrunken nucellar tissue was found in ovules with cellular female gametophytes. Incompatibility rather than embryo inviability is apparently the primary mechanism preventing high crossability between these two species. Forest Sci. 19:50-60.