An opening in the integuments of an ovule that exposes part of the megasporangial wall (a chamber called a pollen chamber in gymnosperms).   Thus, in gymnosperms, pollen enters the micropyle and germinates in the pollen chamber.  However, because the micropyle is not exposed in flowering plants, their pollen germinates on the stigma.  The pollen tube grows through the style, and enters the ovule through the micropyle.