How Does Pollen Reach the Ovule?

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How does pollen reach the ovule? Pollen is transferred to a stigma, and a pollen tube grows down the style to the ovary, where the ovules are. Sperm travel down that tube and join an egg cell inside the ovule. This explainer answers the question directly, walks through the steps in order, and notes where the sources stay general. The steps below come from the Illinois and Penn State Extension pages, with one research paper added for detail.

Quick answer

• Pollen is produced on anthers at the ends of the stamens, and it has to be transferred to the stigma.
• After it lands on the stigma, a tiny tube grows from the pollen grain down the style into the ovary.
• Sperm cells travel down that tube and join an egg cell in the ovule, which causes fertilization.
• Penn State Extension describes the result as fertilization and seed set.

Step one: pollen leaves the anther

Pollen is produced at the ends of the stamens on structures called anthers, according to the Illinois Extension classroom background. The stamen has two parts: the anthers and a filament. Anthers are supported by a thread-like structure called a filament. The female portion of the flower is generally located at the center, and it is called the pistil.

Penn State Extension describes the first step as a pollinator receiving pollen from the male anther at the top of the stamen. The Illinois page says the essential flower parts are the male stamens and the female pistil.

Step two: pollen lands on the stigma

The top part of the pistil is called the stigma. It is sticky, so it will trap and hold pollen, according to the Illinois page. Penn State Extension describes the second step: pollen is deposited on the female stigma at the top of the carpel.

Penn State Extension defines pollination as the transfer of pollen from the anthers of a flower to the stigma of the same flower or another flower. The sources separate the two cases. When the pollen transfer happens within the same flower, it is called self-pollination. When it occurs between different flowers, it is called cross-pollination.

Penn State Extension also says cross-pollination is preferable to self-pollination because it produces more genetic diversity in plant populations.

Step three: the pollen tube grows

Pollen grains land on the stigma, and a tiny tube grows from each grain. The tube grows down the style and into the ovary. The Illinois page says the style is the tube-like structure that supports the stigma, and that it leads down to the ovary, which contains the ovules.

Penn State Extension states the same sequence in its numbered steps. The pollen tube elongates from the pollen grain into the style and down to the ovules, resulting in fertilization and seed set.

Step four: sperm meet the egg

Sperm cells travel down the tube from the pollen grains and join with an egg cell in the ovule, according to the Illinois page. The fertilized ovule becomes the seed, and the ovary becomes the fruit.

A research paper on one species, Sagittaria potamogetifolia, describes the same steps in more detail. The authors say deposition of pollen on stigmas, pollen germination and growth of pollen tubes to ovules are generally regarded as necessary factors that influence the success of sexual reproduction in angiosperms.

Three tube-growth patterns in one species

The Sagittaria study followed the route of pollen tubes through the flower. The authors report that pollen tubes grew through one stigma to the base of the ovary at almost the same speed. Generally, only one of the pollen tubes then turned toward the ovule and finally entered the nucellus through the micropyle.

The study describes three patterns. In the first, if a stigma was pollinated with only one pollen grain, the pollen tube extends through tissue on one side of the pistil, turns toward the other side near the ovary base, and reaches the micropyle from beneath. In the second, when more than one pollen grain was deposited on a stigma, all pollen grains germinated and no pollen tubes stopped growing. In the third, if some stigmas were pollinated later than others, a pollen tube from an adjacent pistil could reach the nucellus before a pollen tube growing down the late-pollinated stigma.

The other pollen tubes did not stop. The authors say they grew through the ovary base and the receptacle tissue into ovules of adjacent carpels whose stigmas were not pollinated, or which had been pollinated later. The study calls this pollen tube reallocation.

The study also reports speed. Some pollen tubes had reached ovaries, or even entered ovules, 2.5 hours after flower opening. The authors say this suggests that pollen tubes grow very rapidly in that species. They add that the establishment of domination in pollen tube competition depends mainly on the temporal order of pollen deposition.

Why flowers need pollinators

Flowers cannot move, so they need to attract pollinators. Penn State Extension says plants work hard to attract their pollinators and offer them rewards. The Illinois page lists sweet nectar, bright colors, and shapes and structures that accommodate particular pollinators as the tools flowers use. Penn State Extension also says plants offer pollen, an important source of protein, and nectar, a concentrated sugar solution, to lure insect pollinators.

Not every flower relies on an animal. The Illinois page says petalless flowers accommodate wind pollination. Penn State Extension says some plants have very lightweight, smooth pollen that is easily blown by the wind from one plant to another.

Some flowers have only one kind of sex part. The Illinois page says flowers may contain either all male parts or all female parts.

For related planting topics, see the guide on how to plant a rose border and the guide on how to plant a shade perennial garden.

How we chose

The Penn State Extension page and the Illinois classroom page are both extension material. The Sagittaria study was added after a web search because the batch pages do not give timing for tube growth. Each source returned HTTP 200 when opened on 2026-10-27 with a plain request.

What we could not verify

The sources describe the same route, but they do not give timing for most plants. The points below are what the pages checked do not settle.

What the sources do not say

• Timing for typical garden flowers. The only timing figure comes from one species, Sagittaria potamogetifolia.
• How many pollen grains a stigma needs. The Illinois and Penn State pages do not give a count.
• How often the tube reaches the ovule. The Sagittaria study reports reallocation between carpels, but the pages checked do not give a general rate.

Frequently asked questions

Does pollen travel through the style?

Yes. Penn State Extension says the pollen tube elongates from the pollen grain into the style and down to the ovules.

What does the stigma do?

The Illinois page says the stigma is sticky so it will trap and hold pollen.

What joins with the egg?

The Illinois page says sperm cells travel down the tube from the pollen grains and join with an egg cell in the ovule.

What is the difference between self-pollination and cross-pollination?

Penn State Extension says self-pollination happens within the same flower, while cross-pollination happens between different flowers.

Can wind move pollen to the stigma?

Penn State Extension says some pollen is easily blown by the wind from one plant to another, because it is very lightweight and smooth.

Sources

• Penn State Extension, Pollination and Pollinators: https://extension.psu.edu/pollination-and-pollinators (opened 2026-10-27)
• University of Illinois Extension, Case 4 Background: https://web.extension.illinois.edu/gpe/tg/c4-background.html (opened 2026-10-27)
• Pollen Tubes Enter Neighbouring Ovules by Way of Receptacle Tissue, Resulting in Increased Fruit-set in Sagittaria potamogetifolia Merr.: https://pmc.ncbi.nlm.nih.gov/articles/PMC4233842/ (opened 2026-10-27)