What is Pollen tube?
[[File:Pollentubes.jpg|thumb|right|Pollen tubes growing from pollen grains (as seen under a [[microscope]])]] The '''pollen tube''' is the tube through which sperm from the [[pollen]] reaches the egg cell, and [[Fertilisation|fertilises]] the plant to form [[seed]]s. The pollen tube of most seed plants acts as a passageway. It transports [[sperm]] cells from the pollen grain, from the [[stigma (botany)|stigma]] (in [[flowering plants]]) to the [[ovule]]s at the base of the [[pistil]]. Like [[fern]]s, other basal land plants, and many [[algae]], some [[gymnosperm]]s have flagellate sperm, which swim through a watery fluid to fertilize the egg cells. [[Image:Mature flower diagram.svg|thumb|400px|center|Diagram showing the main parts of a mature flower]] In [[angiosperms]] the pollen tube germinates from the pollen grain and grows the entire length through the stigma, style, ovary and ovules to reach the [[Ovum|eggs]]. In [[maize]], this single cell can grow longer than 12 inches to traverse the length of the pistil. The sperm cells by themselves are not motile and are carried within the tube. As the tip of the tube reaches an egg it bursts and releases two sperm cells leading to a ''double fertilization''. One sperm unites with the egg cell to produce the embryo of a new plant, while a second sperm unites with the central cell (polar nuclei) to produce the [[endosperm]] of the seed. The endosperm is rich in [[starch]], [[protein]]s and [[oil]]s and is a major source of human food (e.g., [[wheat]], [[barley]], [[rye]], [[oats]], [[corn]]) [[Category:Plant anatomy]] [[Category:Plant physiology]]