Aperture types. A: Pore, tranverse and meridional furrow in the
ektexine; B: same, in the endexine; C: concordant apertures; D: discrodant apertures; porein ektexine,
furrow in endexine; E: the same, furrowin ektexine, pore or furrow in endexine.
Apertures refer to the openings in the sexine.
These openings are classified based on their relative shape: pores and furrows
(colpi). The suggested function of apertures is thought to be the formation of
weak parts in the pollen grain wall through which the pollen tube can emerge at
germination. The difference between furrows and pores seems to be purely
geometric. Furrows are elongate, boat-shaped, and the ends are more or less
acute. Pores for their part are generally isodiametric and, if they are
elongate, the ends are rounded.