A pistil is a female reproductive part of a flower, designed to be fertilized through pollination so that its ovules will develop into seeds, allowing the plant to propagate itself. Often, the seeds occur inside a fleshy layer of material better known as a fruit. Pistils are located inside the flowers of plants, and they come in a variety of shapes and sizes which are specifically adapted to various plants and conditions. They may also be arranged in various ways inside the flower, with some pistils being buried deep inside, while others are thrust out.
Pistils form from leaf-like structures known as carpels. Sometimes a single carpel forms a pistil, and sometimes multiple carpels fuse together. At the base of the pistil, one can find the ovules or eggs. Projecting from the ovules, the pistil has a style, which elevates the anther, a structure which is designed to attract and trap pollen. When pollen lands on the anther, it moves down the style and into the ovules to fertilize the plant.
When the pistil is superior, all of its parts are clearly elevated so that they project from the flower, including the ovules. Intermediate and inferior pistils are buried more deeply into the flower. The position of the pistil plays a role in whether or not a plant can self fertilize, with most plants trying to promote cross-pollination for genetic diversity, rather than fertilizing their own ovules.
People who are interested in plant anatomy can take a look at a pistil the next time they happen to have a flower handy, ideally a large flower such as a daylily so that they will be able to clearly see the structures. If a flower is cut carefully in half to create a cross-section, the viewer should be able to see the bulbous ovules, projecting style, and slightly sticky anther, which together make up the pistil.
Also known as the gynoecium, the pistil is commonly located side by side with the male part of the flower, the androecium. In some plants, the flowers are either male or female, which is designed to promote cross-pollination, and in a few species, the entire plant is either male or female. When plants are gendered like this, it is necessary to have at least one male plant in the vicinity to provide pollen for fertilization. Municipalities sometimes take advantage of this to grow trees which will not produce messy fruit, planting male trees for ornamental purposes.