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 Photo shows a person knocking a cloud of pollen from a pine tree.
A person knocks pollen from a pine tree.
 Photo A shows the long, thin flower male of the white willow, which has long, hair-like appendages jutting out all along its length. Photo  B shows the female flower from the same plant. The shape is similar, but the hair-like appendages are missing.
These male (a) and female (b) catkins are from the goat willow tree ( Salix caprea ). Note how both structures are light and feathery to better disperse and catch the wind-blown pollen.

Pollination by water

Some weeds, such as Australian sea grass and pond weeds, are pollinated by water. The pollen floats on water, and when it comes into contact with the flower, it is deposited inside the flower.

Evolution connection

Pollination by deception

Orchids are highly valued flowers, with many rare varieties ( [link] ). They grow in a range of specific habitats, mainly in the tropics of Asia, South America, and Central America. At least 25,000 species of orchids have been identified.

 Photos depict an orchid with a bright yellow center and white petals.
Certain orchids use food deception or sexual deception to attract pollinators. Shown here is a bee orchid ( Ophrys apifera ). (credit: David Evans)

Flowers often attract pollinators with food rewards, in the form of nectar. However, some species of orchid are an exception to this standard: they have evolved different ways to attract the desired pollinators. They use a method known as food deception, in which bright colors and perfumes are offered, but no food. Anacamptis morio , commonly known as the green-winged orchid, bears bright purple flowers and emits a strong scent. The bumblebee, its main pollinator, is attracted to the flower because of the strong scent—which usually indicates food for a bee—and in the process, picks up the pollen to be transported to another flower.

Other orchids use sexual deception. Chiloglottis trapeziformis emits a compound that smells the same as the pheromone emitted by a female wasp to attract male wasps. The male wasp is attracted to the scent, lands on the orchid flower, and in the process, transfers pollen. Some orchids, like the Australian hammer orchid, use scent as well as visual trickery in yet another sexual deception strategy to attract wasps. The flower of this orchid mimics the appearance of a female wasp and emits a pheromone. The male wasp tries to mate with what appears to be a female wasp, and in the process, picks up pollen, which it then transfers to the next counterfeit mate.

Double fertilization

After pollen is deposited on the stigma, it must germinate and grow through the style to reach the ovule. The microspores, or the pollen, contain two cells: the pollen tube cell and the generative cell. The pollen tube cell grows into a pollen tube through which the generative cell travels. The germination of the pollen tube requires water, oxygen, and certain chemical signals. As it travels through the style to reach the embryo sac, the pollen tube’s growth is supported by the tissues of the style. In the meantime, if the generative cell has not already split into two cells, it now divides to form two sperm cells. The pollen tube is guided by the chemicals secreted by the synergids present in the embryo sac, and it enters the ovule sac through the micropyle. Of the two sperm cells, one sperm fertilizes the egg cell, forming a diploid zygote; the other sperm fuses with the two polar nuclei, forming a triploid cell that develops into the endosperm    . Together, these two fertilization events in angiosperms are known as double fertilization    ( [link] ). After fertilization is complete, no other sperm can enter. The fertilized ovule forms the seed, whereas the tissues of the ovary become the fruit, usually enveloping the seed.

Questions & Answers

what's the meaning of worst
Okebe Reply
it means the time you are wasting to do something
Cyrus
they say one sperm fertilizes one egg so the billions sperm dies instantly?
Sothine Reply
how does the myelin help the motor neutrone to carry out it's functions
Goratile Reply
Where does Lamblia intestinalis live in humans body? Select one: a. Small intestine b. Liver c. Colon d. Brain
Hossam Reply
what is biology
enock Reply
Biology is the study of living things and nonliving things
Godfred
what type of fluid is filled in hydroskeretal system
Ngenda Reply
The phenomenon by which Protoplasm of a cell shrinks from the wall is 
test Reply
turgidity
Ngenda
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Burton Reply
which nevel succulate blood system from harm to hear
Burton
cardio-vein
Ngenda
if an organism is cartilaginous is fully capable of a protecting the internal organs
Verah Reply
what is different between cell and tissue
Rose Reply
cell is the functional and structural unit of life while tissue is a group of cells aggregate to perform a similar or particular function
Tajudeen
cell is the basic unit of life while tissue is group of related cells that perform the same function Eg. the nerve tissue is made up of nerve cells
AAGifty
please what is meant by mutation
Kyere Reply
mutation is the change in DNA which results in the evolution
Shshank
what is binominal nomenclature?
Furaha Reply
the system of naming organisms depending on their xtics of origin
Vincent
The system of naming organisms using two-words Latin names
Agyeiwaa
what is the fate of reduced NAD in cell metabolism
namirembe Reply
what is plant cell
OLUWAKEMI Reply
what is the importance of meoisis
Kamasa Reply
it also aids in formation of pollen grain in anther and formation of ovules in ovary of flowering plant
Orawo
it also aids in formation of sperm or ova in animals
Orawo
What is food chain
Godfred

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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