How does a flower make a seed?

For this example, we'll discuss a sexually perfect flower capable of selfing. That means a flower with both "female" and "male" gametes that can fertilize itself.



Recall that a flower has a structure called a pistil. The pistil is typically in the center of a flower and connects to an ovary in the bottom of the flower, which contains ova (eggs). There are also several smaller structures normally arranged around the pistil called stamen. Stamen create pollen, the "sperm" of a plant. When a pollen granule lands on the pistil, a long germ tube grows from it down the pistil into the ovary. The DNA compliment of the pollen granule moved down the tube and fertilizes a single egg. At this point the haploid pollen and haploid ovum have merged their DNA to create a diploid embryo (plants are complicated, though, and plants with many, many copies of each chromosomes are quite common). The embryo then develops into a seed in the ovary (sometimes this is a fruit). If you've ever seen roses that have lose their leaves and become sort of "fat" around the hips, this is an ovary with several developming embryos, which will develop into seeds.



Imperfect flowers are split into male and female flowers, so that one flower will have a pistil and one will have a stamen. Additionally, some plants are incapable of being fertilized with (or fertilizing) their own flowers. This means that pollen from one plant will need to somehow make it to another plant for fertilization to occur.