Regardless of type, the basic stages of bean plant germination occurring between 1 and 21 days are fairly consistent. The stages of development of the plant are not exact to a day, but depend on the conditions, such as the amount of sunlight, the availability of nutrients and the type of soil in which the bean is planted. The majority of beans prefer a soil temperature of at least 50 degrees F to germinate well. To encourage a faster emergence, consider soaking the seed before planting.
The Seed Transitions
The first stage of germination starts deep within the bean seed. When the temperature is right and there's enough moisture, along with other factors, the seed changes from inert to active. This package holds the potential for development of the entire plant, locked inside a hard protective shell that prevents the embryo from being damaged. The embryo is made up of the basic structures that will form the adult plant. The embryo development is powered by food obtained from the endosperm, which shares the interior of the seed with the embryonic structures. Larger seeds, like bean seeds, contain a greater amount of endosperm. According to the Washington State University Extension, this allows such seeds to be planted deeper in the soil, as they will have an adequate supply of nutrition to sustain them until they reach the surface and gain the opportunity to harness photosynthesis.
The emergence of the root is the first visible sign of germination, but before it appears, the seed soaks up moisture from its surroundings, triggering enzymes to drive cell division. As the cells multiply, the growing root breaks through the exterior of the seed. The root acts as both an anchor for the plant and a conduit for the plant to take in water and nutrients from the soil.
The emergence of the hypocotyl follows. The hypocotyl appears in an arch shape, which helps it to press up and out through the surface of the soil. The hypocotyl pulls the cotyledons--structures that protect the primary leaves--out of the soil. Kimball’s Biology Pages reports that, in response to light, the arch then straightens. The structure then becomes the main stem and support of the plant.
The epicotyl structures emerge. The epicotyl is made up of two leaves--the primary leaves--and the growing tip of the stem called the apical meristem. The leaves emerge from the covering of the cotyledons, which eventually fall away, having served their purpose. The leaves then begin the process of photosynthesis to provide energy to the growing plant.