Planting From Seeds

A seed is a fertilized and mature ovule , consisting of an embryo, one or two cotyledons (seed-leaves) and seed-coat.
Depending on the number of cotyledons, a seed may be classified either as dicot(eudicot) (e.g.,bean), or monocot (e.g., maize,corn).
All monocot seeds are endospermic i.e., the food for the growing embryo is stored in a separate tissue known as the endosperm. In the case of dicot(eudicot) , some seeds are endospermic while others are non-endospermic i.e., the food for the growing embryo is stored in the cotyledons and not in the endosperm.

Structure and Function of Maize and Bean

Maize

The External Structure

Maize grain is not a seed , but a single-seed fruit. Its fruit-wall and seed-coat are fused into a single layer. The grain is monocotyledonous and endospermic. There is a small tube near the top of the grain. A very slight, whitish patch on one side of the grain, marks the embryo. the micropyle is situated at the base of the grain.

The Internal Structure
The outermost layer is formed by the fusion of the fruit-wall and seed-coat. The endosperm constitutes the upper one-third to the three-quarters of the grain. The endosperm has thin outer aleurone layer and and an inner part containing starch grains. The aleurone layer consists of proteins and fats.
A shield-shaped single cotyledon is known as the scutellum.It is separated form the endosperm by the epithelial layer. The embryo is embedded in the scutellum. Its plumule is covered by a sheath called the coleoptile and the radicle by the coleorhiz.

Bean

The External Structure

 The whole seed is covered by a single layer, the seed-coat which is functioning to reduce evaporation from the seed and to protect it against diseases and mechanical injuries. Near the middle of the convex edge of the seed, there is a large oval scar called the hilium where food and water from the fruit-wall is supplied to the young seed.

 

 

 

 

The Internal Structure

On removing the seed-coat, two large kidney-shaped cotyledons are seen closely pressed to each other. They are thick because food is stored in them. When they are apart, there can find a slander acute end of the embryo called the radicle which will grow into the future root. The small feathery structure at the opposite end is the potential shoot. Below the point of attachment to the cotyledons, is the hypocotyl, and the above is the epicotyl.