Facts About Bean Seeds

Beans are the seed of legume plant species.

Beans are seeds produced by plants in the legume family of flowering plants. Some bean plants are bushy, some are vines, but all bean plants produce seeds in a seed pod. The pods are harvested and removed in species like butter beans and pinto beans. Pole beans and green bean varieties are harvested and processed with the pod left on.



Beans are a healthy source of nutrition and contain essential vitamins and minerals. Some species of bean also contain high levels of omega-3 fatty acids which have been shown to aid in lowering blood cholesterol levels.

Testa

The hard outer cover on beans is the testa.

Bean seeds have an outer covering called the testa. This hard outer covering protects the plant embryo inside the bean from physical damage and the loss of moisture. This structure evolved as a means of protecting the seed embryo when beans were wild plants.

According to Washington State School of Biological Sciences, this hard outer shell protects wild seeds during the dispersal process. Many species of beans need to be soaked in water before cooking to soften the testa.

Cotyledon

As a bean plant turns its fertilized flowers into fruit, seeds begin to develop inside the pods. Inside the seed, nutrients are stored to supply the growing bean plant embryo. These nutrients are stored inside specialized leaf structures called cotyledons.

Beans are dicot plants because there are two cotyledons in each bean seed. The majority of the inside of the seed is cotyledons. If you soak a bean for 24 hours in water and then split it in half you can see the cotyledon structures in each half of the seed.

Embryo

The softening of the testa releases enzymes that make the embryo grow.

Inside the bean seed you will find the embryo. This is a tiny embryonic plant made up of three separate parts. The epicotyl is the part of the embryo that will grow into leaves and the stalk of the plant. It is connected by a structure called the hypocotyl to the embryonic root called the radicle. All these parts develop and grow by taking nutrients from the cotyledons.

Germination

Germination is the process whereby a bean seed becomes a bean plant. Moisture in the soil causes the hard outer covering on the seed to soften. According to Washington State University Extension Service, the softening of the testa activates an enzyme in the bean seed that causes the embryo to grow larger. Soon it is too large for the seed to contain it and the radicle emerges into the soil.

The radicle develops into roots that absorb moisture and nutrient mineral from the soil. Next the hypocotyl grows into a hook shape which straightens out to pull the cotyledon from the soil. The first leaves emerge from the cotyledons and photosynthesis can begin. What began as a bean seed is now a growing bean seedling.

History

The Aztecs used beans to pay tribute.

Beans are an important part of a healthy diet and have been for thousands of years. All the types of dry beans sold today are derived from one single species. Phaseolus vulgaris L was first cultivated in South America over 7,000 years ago by the Pre-Colombian Native American people.

According to the Purdue University Horticulture Department, the red beans were valued as a protein source because animal protein was not a major component in the food supply. The Aztecs and Incas valued beans so highly that they used them to pay tribute.

References

• Washington State School of Biological Sciences: Seeds
• Washington State University Extension: Gardening in Western Washington-Seed Germination
• Purdue University Horticulture: Beans

Resources

• Heirlooms.org: Heirloom Beans