Pollination and Fertilization

Summary

All conifers rely on wind to move pollen to ovule but form matters as much as chance; pollination is more akin to coordination and synchrony than it resembles a stochastic process. During female strobilus receptivity, ovules exude a localized pollination drop at night. By early morning, the pollination drop retracts, pulling its captured grains inside the micropylar arms, closer to the spongy nucel-lus. Hydrated by the pollination drop, the pollen grain now germinates into the spongy nucellar tissue. The pollen tube then halts its growth midway through the nucellus during the lengthy interval between pollination and fertilization. During this interval, the female gametophyte completes its development, slowly expanding to its maximum size and forming multiple archegonia. The duration of the pollination-fertilization interval is taxon-specific, lasting many months. The pollen grain resumes its growth a few days before fertilization then delivers one or two male gametes to the egg cell. The close synchrony between male and female reproduction is a sharp contrast to heterospory-induced divergence.