Source : Webster's Revised Unabridged Dictionary (1913)

Ostiole \Os"ti*ole\, n. [L. ostiolum a little door, dim. of
   ostium a door: cf. F. ostiole.] (Bot.)
   (a) The exterior opening of a stomate. See {Stomate}.
   (b) Any small orifice.

Source : WordNet®

ostiole
     n : a small pore especially one in the reproductive bodies of
         certain algae and fungi through which spores pass