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Webster 1913 Edition

Noun.

[L.

ostiolum

a little door, dim. of

ostium

a door: cf. F.

ostiole

(Bot.)

(a)

The exterior opening of a stomate. See

(b)

Any small orifice.

ostiole ‎(plural ostioles)

(mycology) A small hole or opening through which certain fungi release their mature spores.
(botany) A similar hole or opening in plants, such as the opening of the involuted fig inflorescence through which fig wasps enter to pollinate and breed.