Reproduction in plants

To round up my final question of research (organisms other than mammals that reproduce), the topic on reproduction and the biojournal in general, I will end off with the topic of research on reproduction in flowering plants. This is my only post where I will talk about something out of the animal kingdom.



Well, firstly we must understand that the flowering plant has male and female organs too. Male organs are collectively called the androecium. The parts include the stamen, which consist of the filament which supports the anthers. The anther contains four microsporangia within which microspores (pollen) are produced by meiosis. Inside the pollen are two (or, at most, three) cells that comprise the male gametophyte. The tube cell (also referred to as the tube nucleus) develops into the pollen tube. The germ cell divides by mitosis to produce two sperm cells.
Female organs are collectively known as the Gynoecium. The gynoecium consists of the stigma, style, and ovary containing one or more ovules. These three structures are often termed a pistil. The stigma functions as a receptive surface on which pollen lands and germinates its pollen tube. The style serves to move the stigma some distance from the ovary. The ovary contains one or more ovules, which in turn contain one female gametophyte, also referred to as the embryo sac.
So for the stigma to even get pollens and reproduce, something known as pollination must occur. This is accomplished by a variety of methods. Entomophyly is the transfer of pollen by an insect. Anemophyly is the transfer of pollen by wind. Other pollinators include birds, bats, water, and humans. Some flowers (for example garden peas) develop in such a way as to pollinate themselves. Flower color is thought to indicate the nature of pollinator: red petals are thought to attract birds, yellow for bees, and white for moths. Wind pollinated flowers have reduced petals, such as oaks and grasses.
The process of pollination being accomplished, the pollen tube grows through the stigma and style toward the ovules in the ovary. The two sperm cells will move down the pollen tube. Once the tip of the tube reaches the micropyle end of the embryo sac, the tube grows through into the embryo sac through one of the synergids which flank the egg. One sperm cell fuses with the egg, producing the zygote which will later develope into the next-generation sporophyte. The second sperm fuses with the two polar bodies located in the center of the sac, producing the nutritive triploid endosperm tissue that will provide energy for the embryo's growth and development.
After fertilization, the zygote divides mitotically. The product of this repeated nuclear division and cell multiplication is an embryo. The seed will now develop. The development consists of a conversion of the integument of the ovule into a resistant seed coat, the development of the endosperm, and the development of the embryo. All these events take place within the original ovary.
A section through a nearly mature seed will reveal an embryo consisting of two large cotyledons with a small epicotyl between them attached to the hypocotyl. Most or all of the endosperm has been absorbed by the cotyledons and the integuments of the ovule have grown into a seed coat. The basal portion of the embryo is termed the radicle. The epicotyl develops into the above ground structures of the plant (stem, leaves, flowers). The radicle develops into the true root system while the hypocotyl develops into the transition zone between root and stem.
The seed will usually lay in the ovary wall which has been devloped into a fruite. The seed will then disperse by either wind, air, animals or water and germinate themselves.
I thank http://io.uwinnipeg.ca/~simmons/lb4pg12.htm and http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookflowers.html for the info