Blog Post Assignment 10: Anthers and Stigmas and Styles, Oh My!

We dissected the flower of a Brassica oleracea with a dissecting microscope in order to see the parts inside. Here are pictures we took of various parts we found. All pictures (except for the first one) are from an iPhone through the lens of a dissecting microscope at 40x magnification.

The Brassica oleracea flower, unmagnified, before dissection.

The male reproductive anatomy of a flower is made up of an anther and a filament, which together are called the stamen. The filament is the long green stalk coming up from the base of the plant, and the anther is the small sack on top of the filament. The anther is where meiosis happens and where pollen containing sperm cells is produced.

The female anatomy of the flower is called carpels, made up of the style, the stigma, and, at the base of the carpel, the ovary. The ovary contains ovules where female gametophytes are created. The long stalk is the the style. The sticky thick part at the top of the style is the stigma, where pollen grains are supposed to be deposited.

Here is a picture showing the female anatomy, the carpel, surrounded by the male anthers. This flower, from Brassica oleracea, has both the carpel and the stamen, which some plants do not have.  The pollen created from 4 haploid spore cells in the anthers eventually stops growing and is deposited on the stigma. If the cells go through meiosis and then mitosis properly, one of the outlasting eight nuclei (created in mitosis) is the egg nucleus - female gamete.

This is the ovary cut open to reveal the ovules. The ovules are the tiny round balls, and they contain the female gametophytes.

This is an individual ovule or unfertilized seed.

This is some pollen that we collected from the anther. We used a wet mount slide to get the picture.

In a flowering plant species like Brassica oleracea, fertilization is outside the flower even though the flower contains the stamen and carpel. When there is a flower, the anthers inside go into meiosis and create four haploid spore cells. These cells become a single pollen grain. Eventually, the nucleus of each pollen grain undergoes mitotic division to create haploid nuclei. The pollen grain eventually stops growing and is deposited on the stigma. In the ovary, a single diploid cell goes through meiosis and produces 4 haploid cells, three of which disintegrate. The leftover 1 cell goes under mitosis to create 8 nuclei. These 8 nuclei are part of the embryo sac, which is the female gametophyte. One of these 8 nuclei is the female gamete. Once the gametophytes are developed, they will be pollinated. In angiosperms, fertilization is when pollen on a stigma creates a pollen tube and the nucleus in the pollen divides and makes two sperm nuclei. The pollen tube grows into the style and enters the ovary and ovules. There, two fertilizations  happen. One sperm nuclei fuses with the egg nucleus to make a diploid zygote. The zygote will be the new plant embryo. The other sperm fuses with two endosperm nuclei in the embryo sac. This cell will be endosperm, nourishment for the seed. Now that fertilization has occurred, the embryo will become a new plant.