Anatomy of a Seed

Seeds are the dispersal and propagation units of most plants. There are three basic parts of a seed in the angiosperms: (a) an embryo, (b) a food storage or nutritive tissue, and (c) seed covering. Seed anatomy is specifically designed as a self-contained unit which, under the right conditions, will become a living plant.

Anatomy of a Seed Definitions

Seed Coat (Testa)

A tough, hard, outer coat, the testa protects the seed from fungi, bacteria and insects. It has to be split open by the radicle before germination can proceed. The testa also has two anatomical features that might be a little harder to identify: The hilum is a scar left by the stalk which attached the ovule to the ovary wall. The micropyle is a tiny pore in the testa opposite the tip of the radicle. It admits water to the embryo before active germination.

Plumule

The plumule is the embryonic shoot. In it two or more leaves are usually visible, with a growing point enclosed between them.

Hypocotyl

The part of a plant embryo or seedling plant that is between the cotyledons and the radicle or root. In a seedling it is the sprout structure above ground that supports the Cotyledon (first leaves).

Radicle (Tap Root)

The radicle is the embryonic root which grows and develops into the root system of the plant.

Cotyledon

The grasses and narrow-leaved plants like the iris and bluebell have seeds with only one cotyledon. The other flowering plants all have two cotyledons. They are leaves attached to the plumule and radicle by short stalks, and they often contain food reserves which are used during the early stages of germination. In most plants the cotyledons are brought out of the testa and above the ground where they become green and make food by photosynthesis. The cotyledons eventually fall off, usually after the first foliage leaves have been formed. The cotyledon leaves bear no resemblance to the foliage leaf, the shape of which is first apparent when the plumule leaves open and grow.

Epicotyl

The epicotyl is the embryonic shoot above the cotyledons. In most plants the epicotyl will eventually develop into the leaves of the plant. In dicots, the hypocotyl is what appears to be the base stem under the spent withered cotyledons, and the shoot just above that is the epicotyl.