pollen tube

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A slender tube that is formed by a pollen grain of a seed plant and penetrates the ovule, where it releases the male gametes.

from The Century Dictionary.

• noun In botany, the tube through which the fecundating element is conveyed to the ovule.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun the tube that develops from the wall of a pollen grain and, in seed plants, provides a passage through which the male nuclei reach the embryo sac to effect fertilization

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• 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