Why do pine pollen grains have two air bladders?

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Stone pine trees with rounded canopies stand amid low shrubs and flowering yellow bushes in Donana National Park, Huelva province, Andalusia, Spain. — pine A stand of stone pines (*Pinus pinea*) in Doñana National Park near Seville, Spain.

Pine pollen grains possess two air bladders, also known as sacci, to facilitate effective pollination. Because pine trees rely on wind for reproduction, these structures serve a specific mechanical purpose: they orient the pollen grain correctly within the pollination droplet exuded by the ovule.

This precise orientation ensures that when the pollination droplet is withdrawn back into the ovule, the pollen grain is positioned so that the pollen tube can accurately penetrate the nucellus and reach the archegonium for fertilization.1