6.2.2. General Parts of a Dicot Seed

● Seed Coat – Outer protective covering; consists of two layers: ○ Testa – Outer layer ○ Tegmen – Inner thin layer

The seed coat is the outer covering of the seed, providing protection to the inner components. It is made up of two parts: the 'testa', which is the hard outer layer, and the 'tegmen', which is a thin layer inside the testa. Together, these layers help keep the seed safe from physical damage and prevent water loss.

Think of the seed coat like the shell of a nut. Just as the shell protects the nut inside, the seed coat protects the embryo and food supply until the seed is ready to germinate.

● Hilum – Scar on seed coat marking the point of attachment to the fruit

The hilum is a small scar on the seed coat that indicates where the seed was attached to the fruit from which it came. This scar is a reminder of the seed's linkage to its parent plant and is crucial for understanding how seeds disperse and grow.

Imagine a sticker on a fruit. When you peel the sticker off, a little mark remains where it was stuck. That's similar to how the hilum remains as a mark where the seed was attached to the fruit.

● Micropyle – Small pore near hilum; allows entry of water and oxygen

The micropyle is a tiny opening located near the hilum. This small pore is vital as it facilitates the entry of water and oxygen into the seed, which are necessary for germination to occur. By allowing these elements in, the micropyle plays a key role in starting the growth process once conditions are favorable.

Think of the micropyle like a small door on a locked box. When conditions are right (like having a key), the box opens to allow what’s inside to access the outside world, similar to how the micropyle allows water and oxygen into the seed.

● Cotyledons – Two fleshy structures that store food

Cotyledons are the two initial leaves that develop from a seed. These fleshy parts serve as storage organs, providing the necessary nutrients for the developing embryo until it can produce its own food through photosynthesis. In dicot seeds, these are particularly prominent and play an essential role in early growth.

You can think of cotyledons like a packed lunch for a child. Just as a packed lunch provides food until the child can eat from the cafeteria, cotyledons provide stored food for the plant embryo until it can generate its own energy from sunlight.

● Embryo – Develops into the new plant; consists of: ○ Radicle – Grows into root ○ Plumule – Grows into shoot

The embryo is the part of the seed that develops into the new plant. It contains two main parts: the radicle, which will grow into the root, and the plumule, which will grow into the shoot. This differentiation is crucial as it sets the stage for the plant's growth above and below ground.

Imagine planting a garden. The radicle is like the roots of a plant digging into the soil to find nutrients while the plumule is like the stem and leaves reaching up for the sun. Both parts are essential for the plant's survival and growth.

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