Information on Broad Bean Germination

Some good information from the The National Council for the Conservation of Plants and Gardens website

The seed and seedling of the broad bean Vicia faba

While all of us are careful as we sow our seeds, we spend little time in concentrating upon the structure and germination of the seed itself.Seeds of Dicotyledons have two seed leaves or cotyledons, hence the name, while seeds of Monocotyledons have only one cotyledon. Most of our trees and shrubs and plants with branched veins belong to the first group, while the plants with parallel veins, i.e. all our bulbs, grasses, sedges and rushes, belong to the second group.The Broad Bean seed is formed in a large pod or legume.
The extra large seed, if soaked for 12 hours, will reveal, when dissected, its unique and intriguing structure. First observe the seed coat or testa, which is impervious to water. Squeeze the soaked seed slightly and you will notice a slight bubbling coming out of a little hole, known as the micropyle. This is where the water essential for germination gets into the seed. Near the micropyle there is a dark scar where the seed was attached to the mother plant in the bean pod, and that is termed the hilum. With your finger nails peel off the testa or seed coat and you will find two sections which are known as cotyledons. These cotyledons store starch which was obtained from its parent. When germination starts to take place this starch is converted into sugar and will give the necessary energy for germination to take place.In between the two cotyledons you will find an embryonic shoot with vein markings and an embryonic root. The embryonic shoot is called the plumule, while the embryonic root is termed the radicle. The radicle develops first by pushing its way through the soil and developing root hairs just behind the root cap which take in water and mineral nutrients by the process of osmosis. In the broad bean the plumule acts as the first pair of leaves by going green and carrying out the process of photosynthesis. In other Dicotyledons it is the paired cotyledons that form the first pair of leaves, e.g. tomatoes, lettuces, French beans and brassicas, etc. It is unique that in the broad bean the cotyledons stay below ground and eventually rot as the seedling develops into adulthood.