Flower Botany Basics
Plants have three female parts which together create the pistel: the stigma, the style and the ovary. The stigma is a bulb on the end of the long, stalk-like style which connects to the ovary inside the petal. Pollen is caught by the stigma and then tunnels down through the style to fertilize the ovules in the ovary. The ovules are like small eggs. Once they are fertilized by the pollen, they begin to develop into seeds which can then grow new plants. The pollen itself comes from the male organ, the stamen. The pollen is suspended from a sac called the anther at the end of a stalk called the stamen.
It's hard to understand the adaptation of the stigma without understanding the whole pollination system. In plants pollinated by insects or other animal pollinators, the flower generally produces nectar or strong scents to attract animals or insects. These animals or insects bump into the anther, and pollen sticks to them. When they go to feed on nectar in another flower, they will bump into the flower stigma, transferring pollen to it. The stigma has adapted to be sticky to hold onto the pollen. The stamen has evolved a style to hold the stigma in a position where it will be bumped into by pollinators. In wind pollinated plants, longer styles hold the stigmas out further where they are more likely to catch pollen.
Plant stigmas often adapt special shapes to make it easier to catch pollen. Some plants evolve broad, feathery stigmas or stigmas with tiny hairs. These stigma adaptations are especially useful in wind-pollinated plants. Wind pollinators such as grasses can not lure pollinators in. They have to catch pollen floating on the wind by chance. The more surface area the stigma has, the better the odds of catching pollen and reproducing.