R2101 – seed structure

The diagram above is a typical seed cross-section. You may need to either draw this, or put the labels on a diagram. You may also be asked to define the parts.

• Testa = the seed coat
• Cotyledon = the seed leaves and food store (remember, monocots only have one of these, whilst dicots have two)
• Endosperm is a food store, but not all seeds have this
• Plumule = forms the first shoot
• Radicle = forms the first root
• Epicotyl = elongates to grow the shoot and attaches the plumule to the cotyledon
• Hypocotyl = elongates to grow the root and attaches the radicle to the cotyledon
• Hilum = the scar showing where the seed was attached to the ovary
• Micropyle = a small gap where the pollen entered the ovule and often the place where water enters the seed to begin germination.

There are two types of germination: Epigeal and Hypogeal.

Epigeal germination is where the cotyledons emerge above ground and you see them. Example: Phaseolus vulgaris (french bean)

Hypogeal germination is where the cotyledons remain below ground, so you just see the true leaves of the plant. Example: Vicia faba (broad bean)