Style of a Flower: Function, Lesson & Quiz
This lesson will explore the reproductive organ of the flower with a focus on the structure known as the style. The lesson will also focus on the function and variation in types of styles among different types of flowering plants.
What do you think of when you hear the word 'style'? Most people think of style as a distinctive way something is done, a manner of expression, or a unique sense of fashion. For flowering plants, style takes on a whole new meaning.
In plants, the style is a structure found within the flower. It is a long, slender stalk that connects the stigma and the ovary. The stigma is at the top of the style and is a sticky platform where pollen is deposited. The ovary is located at the bottom of the style and houses the plant's ovules, which contain the egg cells and supporting cells necessary for reproduction. When combined, these three structures - the stigma, style and ovary - are referred to as the pistil.
The pistil is the female reproductive organ of the flowering plant, and the three structures of the pistil work together to ensure fertilization and plant reproduction. First, pollen, which contains the male genetic information, lands on the stigma and is held in place due to the sticky surface. As the pollen grain germinates on the stigma, it creates a pollen tube which it will use to burrow through the entire length of the style. The pollen tube grows out of the pollen grain and creates a tunnel from the stigma to the ovary.
When the pollen tube reaches the ovary, two sperm cells are released from the pollen grain and are able to travel from the pollen grain down to the ovary. The sperm then fertilize the egg that is waiting in the ovule. After fertilization, the ovule develops into the seed or fruit of the plant and if uneaten, results in the creation of another plant of the same species.
The style is very important during the fertilization process because not only is it the location where the pollen tube forms, but it is also involved in stopping incompatible pollen from penetrating the ovary. When the pollen tube starts to extend within the style, genetic information is exchanged between the pollen and the plant. At this time, the plant also creates a toxin. If the pollen is incompatible due to being from a different species or being too closely related, thus resulting in inbreeding, the plant will release the toxin to stop the growth of the pollen tube. If the pollen is compatible, the plant will sequester, or isolate, the toxin so that it does not stop the growth of the pollen tube. Therefore, the style is the location where compatibility is checked and where the decision is made about whether the pollen that lands on the flower will be permitted to fertilize the plant.
Variation in Styles
There is wide diversity in the design and appearance of the female reproductive organs of flowering plants. One of the major design differences is the position of the ovary, which in turn alters the length of the style. There are three different ovary positions found in flowering plants, including superior ovary, centrally-positioned ovary, and inferior ovary.
Superior ovary placement, also known as hypogynous, is when the ovary is located above the petals and sepals. A flower with a superior ovary has a medium length style. A centrally-positioned ovary, also known called perigynous, is when half of the ovary is above the petals and sepals and half is below. These flowers are often larger and have elongated styles due to the deep location of the ovary within the flower. A flower with an inferior ovary, or epigynous, has an ovary that is located below the petals and sepals. These flowers are often condensed and have a shorter style.
The styles of different flower species also vary a great deal in shape and thickness. Most styles are narrow and straight like a stick, but some are thicker and triangular. Flowers that have thicker styles often have larger stigmas or a branching pattern with multiple stigmas; therefore they need a thicker style to support the distinctive stigma.
The style of a flower is the stalk that supports the stigma and connects it to the ovary. One major function of the style is to assist with fertilization by being the location where pollen tubes travel to deliver sperm cells to the egg. The other major function of the style is to help defend the ovary from pollen that is incompatible with the plant. Although the style of every flower has the same function, they do vary a great deal in length, thickness and shape, giving different flower species a unique look.
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