Most flowers contain both male and female sex cells. The typical flower has four main parts: an outer cup of leaflike sepals, a ring of petals within the sepals, and inside, male reproductive organs surrounding female parts. Male cells develop in structures called stamens and travel enclosed in the hard shell of pollen grains. Female cells, or ovules, develop deep in a flower’s ovary, enclosed in a structure called a pistil. The top of the pistil known as the stigma is long and sticky and a good target for pollen. After it reaches the stigma, a small tube grows out of the pollen grain. The male cells travel down the pollen tube, eventually reaching female ovules. Then fertilization occurs and seeds start to grow.