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A short class with Sarah and her students. The other ways are under More.
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A bee carries pollen from one flower to another flower on the same plant. Is that self- or cross-pollination?
Cross-pollination, because two different flowers are involved.
Many people say that. But both flowers are on the same plant, so the pollen carries the plant's own genes. We call this geitonogamy.
So it works like cross-pollination but counts genetically as self-pollination?
Exactly. Autogamy is within one flower, geitonogamy is between flowers of one plant, and xenogamy is between different plants.
And only xenogamy brings in genes from another plant.
Viola and Commelina make some flowers that never open. What kind of pollination can happen inside them?
Only autogamy, because no pollen from outside can get in.
Right. The anthers dehisce inside the closed flower, right next to the stigma. These are cleistogamous flowers.
Then the plant gets seeds even if no pollinator visits?
Yes, that is the advantage: assured seed set. The cost is that no genes come in from another individual, so variation stays limited.
Maize has male and female flowers on the same plant. Does that prevent self-pollination?
It prevents autogamy, but pollen can still reach another flower on the same plant.
Correct. It stops autogamy but not geitonogamy. Which condition stops both?
Dioecy, as in papaya, where each plant is either male or female.
Good. Other plants separate pollen release and stigma receptivity in time, which is dichogamy, or reject their own pollen through self-incompatibility.
autogamy (same flower), geitonogamy (another flower, same plant) and xenogamy (a different plant).
functionally like cross-pollination because it needs an agent, but genetically self-pollination.
flowers that never open are always autogamous and set seed without pollinators.
dioecy, dichogamy, herkogamy, heterostyly and self-incompatibility discourage self-pollination.
monoecious plants prevent only autogamy, while dioecious plants prevent both autogamy and geitonogamy.
Garden pea: pollen is shed onto the stigma before the flower opens, so pea is normally self-pollinated, which is why Mendel had to emasculate pea flowers to cross them.
Maize: pollen from the tassel falling on the silks of the same plant is geitonogamy, while pollen blown to the silks of a neighbouring plant is xenogamy.
Papaya: where each plant is either male or female (dioecious), every successful pollination must be xenogamy.
Auto at home, geitono next door on the same stem, xeno from afar brings the genetic gem.
A pollen grain wanted adventure. Staying in its own flower was autogamy, a short hop to a sister flower was geitonogamy, but only when the wind carried it to a distant plant did it bring something truly new: xenogamy.
A-G-X goes from near to far - Autogamy (same flower), Geitonogamy (same plant), Xenogamy (another plant).
D.D.H.H.S. - Dioecy, Dichogamy, Herkogamy, Heterostyly, Self-incompatibility, the five outbreeding devices.
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What is geitonogamy?
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Why is geitonogamy called genetically self-pollination?
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Which type of pollination is guaranteed in cleistogamous flowers?
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Which condition prevents both autogamy and geitonogamy?
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What is protandry?
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Transfer of pollen from the anther to the stigma of the same flower.
Transfer of pollen to the stigma of another flower on the same plant.
Transfer of pollen to the stigma of a flower on a different plant of the same species.
A flower that opens, exposing its anthers and stigma.
A flower that never opens and is therefore always self-pollinated.
Maturation of the anthers and the stigma of a flower at different times.
A genetic mechanism that stops a plant's own pollen from fertilising its ovules.
Removal of the anthers from a bisexual flower bud before they dehisce, as done in artificial crossing.
Pollination is classified by where the pollen comes from: autogamy (the same flower), geitonogamy (another flower on the same plant) and xenogamy (a flower on a different plant). This lesson explains each type and the floral features that favour or prevent them.
Autogamy and geitonogamy both bring pollen from the same plant, so they are grouped as self-pollination, while xenogamy brings genetically different pollen and is true cross-pollination. Geitonogamy is the interesting middle case: like cross-pollination it needs a pollinating agent, but genetically it is the same as self-pollination. The lesson also covers cleistogamous flowers, which guarantee autogamy, and the outbreeding devices, such as unisexual flowers, dichogamy, heterostyly and self-incompatibility, that plants use to encourage cross-pollination.
Pollination is the transfer of pollen grains from an anther to a stigma. Asking "where did this pollen come from?" gives three types.
Pollen reaches the stigma of the same flower. For this to happen, the anthers and stigma must lie close together, and pollen release must coincide with the stigma becoming receptive.
Pollen moves from the anther of one flower to the stigma of another flower on the same plant. It needs a pollinating agent, so functionally it resembles cross-pollination. But the pollen comes from the same plant and so carries the plant's own genes, so genetically geitonogamy is a form of self-pollination.
Pollen moves to the stigma of a flower on a different plant of the same species. It is the only type that brings genetically different pollen to the stigma, and so the only one that brings in genes from another individual. It always depends on an agent: wind, water or animals.
Continued self-pollination can lead to inbreeding depression, so many flowering plants have features that discourage it:
Breeders who want one particular cross must stop autogamy and keep out stray pollen. In a bisexual flower they remove the anthers before they dehisce (emasculation) and cover the flower with a bag, usually of butter paper (bagging). When the stigma is receptive, pollen from the chosen male parent is dusted on it and the flower is bagged again. In plants with unisexual flowers, the female flower buds need only to be bagged.