'Pollen tube' definitions:

Definition of 'pollen tube'

noun

(botany) a slender tubular outgrowth from a pollen grain when deposited on the stigma for a flower; it penetrates the style and conveys the male gametes to the ovule

Definition of 'Pollen tube'

From: GCIDE

Pollen \Pol"len\, n. [L. pollen fine flour, fine dust; cf. Gr. ?]
1. Fine bran or flour. [Obs.] --Bailey. [1913 Webster]
2. (Bot.) The fecundating dustlike cells of the anthers of flowers. See Flower, and Illust. of Filament. [1913 Webster]
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. [1913 Webster]

Definition of 'pollen tube'

From: GCIDE

Spermatophyta \Sper`ma*toph"y*ta\, n. pl. [NL.; spermato- + Gr. ? plant.] (Bot.) A phylum embracing the highest plants, or those that produce seeds; the seed plants, or flowering plants. They form the most numerous group, including over 120,000 species. In general, the group is characterized by the marked development of the sporophyte, with great differentiation of its parts (root, stem, leaves, flowers, etc.); by the extreme reduction of the gametophyte; and by the development of seeds. All the Spermatophyta are heterosporous; fertilization of the egg cell is either through a
pollen tube emitted by the microspore or (in a few gymnosperms) by spermatozoids.
Note: The phrase "flowering plants" is less distinctive than "seed plants," since the conifers, grasses, sedges, oaks, etc., do not produce flowers in the popular sense. For this reason the terms Anthrophyta, Phaenogamia, and Panerogamia have been superseded as names of the phylum by Spermatophyta. [Webster 1913 Suppl.]