Question

Describe the structure of a dicot seed.

Answer 1

Hint: A dicot seed is a non-endospermic seed where endosperm is used up during seed development and food is stored in the two cotyledons.

Complete answer:
A dicot seed primarily consists of two basic parts- seed coat and embryo. The surface of the seed may be smooth or wrinkled. An outer seed coat ‘ tegmen’ and an inner seed coat ‘testa’ covers the seed coat. Testa is leathery, thick, and tough while tegmen is thin, fragile, conspicuous, and papery. It lies closely in contact with testa.

A small notch or furrow bearing ‘Chalaza’, in the middle, is present near the broad end of the seed. In the ovule, it was the site of attachment of nucellus and integuments. On the same side, near the pointed end, a scar is present, known as hilum. The seed is connected to the pod by funiculus or stalk. When the seeds are shed, a scar or hilum appears. A small pore known as micropyle is present near the hilum. Water and air enter through this pore.

The embryo is enclosed in the seed. The embryo contains a short and straight embryonal axis. Two large and broad cotyledons or seed leaves are attached to it by slender and tiny stalks. The radicle or the future root is the tip of the embryo axis. It lies towards the micropylar end. Plumule or the future shoot is located deeper between the cotyledons.

Note: The area of the embryo between the point of attachment of the cotyledons and the plumule is described as the epicotyl while the region between radicle and the place of origin of cotyledons is termed as hypocotyl. The majority of dicots e.g. pea, gram, bean, and some monocots like orchids are non-endospermic.