- Before fruit can form, a flower needs to be pollinated. This is not to be confused with fertilization, which takes place later. Pollination occurs when an insect moves the pollen from the stamen into the style. The pollen makes its way down the style, which is a tube-like structure, and into the ovary. The ovary is the slightly swollen part at the base of the flower where it attaches to the petiole or stem. Once the pollen is in the ovary, fertilization takes place.
- The ovary in a flower becomes the fruit. Ovaries are the basal part of the pistil. The organ is enlarged and contains ovules attached to the inner wall. Each ovule contains one egg, which develops into a seed after fertilization. Flowers lose their petals, sepal and other parts after fertilization, and only the ovary is left behind on the petiole. The exterior of the ovary is called the pericarp, which surrounds the carpel. Inside the ovary, the ovules develop into the peas, or edible seeds of the fruit.
- Peas are single-carpel fruits that are dihiscent on two sides. This means they open to release the seeds. Some plants have multiple carpels that may be united to create one fruit, or separate, where each carpel produces a fruitlet. Legumes all have single-carpel flowers. The pea plants are known as simple fruit, which means they grow from one ovary. The inner wall of the ovary is the placenta, where the seeds attach on one side. When you open a pea pod, it is obvious which parts developed into the entire fruit.
- The pericarp thickens as the fruit develops from the ovary and the carpel separates to form the characteristic splits along the sides of the pod. The pericarp becomes the pod and has three layers. The exocarp becomes the outer layer, the mesocarp is the center layer and the endocarp is the inner layer. You can peel some of the layers away with a fingernail and see that they are similar to the layers of skin in human beings.