Micropyle

Micropyle (from the Greek mihron, "small;" pulon, "a door") is the name of the opening left at the distal end of the ovule in seed-bearing plants when the coats of the ovule (primine and secundine) grow up over it. The outer opening, through the primine, which is sometimes the wider, is known as the exostoma; the inner, through the secundine, as the endostoma. Through the micropyle the pollen-tubes pass in the process of fertilisation in angiosperms; but in gymnosperms the pollen-grain itself falls into the micropyle, where it is retained by a secreted drop of honey. The micropyle persists through the various changes of the coats until the seed is ripe, when it may be visible to the naked eye or can be easily detected by soaking the seed and then squeezing it, a jet of yvater issuing from it. In the sprouting of the seed the radicle or primary root first finds its way out through the micropyle.