The Collaborative International Dictionary of English v.0.48:
Pollen \Pol"len\, n. [L. pollen fine flour, fine dust; cf. Gr.
1. Fine bran or flour. [Obs.] --Bailey.
2. (Bot.) The fecundating dustlike cells of the anthers of
flowers. See Flower, and Illust. of Filament.
Pollen grain (Bot.), a particle or call of pollen.
Pollen mass, a pollinium. --Gray.
Pollen sac, a compartment of an anther containing pollen,
-- usually there are four in each anther.
Pollen tube, a slender tube which issues from the pollen
grain on its contact with the stigma, which it penetrates,
thus conveying, it is supposed, the fecundating matter of
the grain to the ovule.