Beans are a very important part of the food chain. They fill many different needs including being a major source of protein and oil. Beans are very easy to grow and understanding the different parts in the structure of the bean will help you understand the growth process.
The testa is the outer covering of the bean. It is usually very thin but tough and can be almost any color depending on the type of bean. Within the surface of the testa, there is a tiny opening called the micropyle, which is where water can enter and start the germination process, breaking the dormant stage.
The cotyledons are the two large parts of the bean seed that take up most of the space within the bean. These serve as food storage for the young bean plant until it grows large enough to support itself. In the middle of the two cotyledons is the tiny embryo, waiting to grow.
The embryo is the infant plant made up of two parts: the radicle, or the first root, and the plumule, or the first leaves. When water enters the micropyle, the radicle starts growing and moves down and out through the micropyle into the soil below. Then the plumule swells and grows, pushing its way through the testa and up through the soil until it reaches the light.
The hilum, or scar, on a bean is the site where the bean originally attached to the fruit of the plant. It is the 'navel' of the bean and can be found on the indent of the bean on the surface of the testa.
The hypocotyl is the area between the root and the cotyledons. It will grow and become part of the stem where it connects to the root.
The epicotyl is the area above the cotyledons and below the plumule. It will grow and become the stem of the plant.