Germinations

Germination is the series of changes occurring in an embryo and resulting in a seedling. Most seeds germinate by either of two methos, epigeal and hypogeal.
In the series of germination procedure, there are a lot of requirements that the seeds are going to need to be growing and to be a young plant. Moist soil, water, carbondioxide gas,oxygen gas, nitrogen compounds, and sunlight are the factors that influence germination of seeds.

Germination of a bean seed

Early stage of bean

In this stage, the seed-coat bursts by absorbing water from moist soil. After two or three days, the embryo starts growing and the radicle pushes through the seed-coat. Whenever the direction the seed is sown, the radicle turns and grows downwards to enter the soil because of geotropism. As soon as the radicle has anchored the seed in the soil, it begins its function of absorbing water and dissolved salt.

The root growth during hyopcotyl appears

Rising up hypocotyl loop

cotyledons emerge

In this stage, the hypocotyl elongates markedly. Because it is attached to the cotyledons and the potential shoot at one end and to the radicle at the other, the elongation results in a loop above the ground. By the time, the radicle has become firmily established as a tap-root with the development of many lateral roots.

lateral roots

growing and elongation

The portions of the cotyledons and hypocotyl which become exposed to sunlight, turn green due to the formation of chlorophyll.

Beginning for first leaves

Hypocotyl loop Straightens up

Root-growth while foliage leaves emerge

In this condition, the hypocotyl loop straightens you, pulls the potential shoot and the cotyledons from the seed-coat in the soil and raises them above the ground.

Cotyledons spreading out

The cotyledons spread out, turn green and become the first pair of leave.Although they can photosynthesize, they are not thin like true leaves, because of the stored food.

When the true green leaves emerge, the cotyledons shrivel you and fall off.

Before cotyledons shrivel up

A new bean plant with its true leaves and terminal bud

the bean leaf

Germination of a maize grain

Maize grain is monocotyledonous arid endospermic and the germination is the hypogeal type.

 

In this stage, the grain absorbs water,swells up and becomes soft through the xylems, when the grain is sown in moist soil. The radicle elongates and pushes out the coleorhiza.The coleorhiza can just be seen as a very small white protuberance near the base of the grain.

coleoptile of a maize grain

The radicle grows through the coleorhiza and anchors the germinating grain to the soil. It then develops into the primary root. The primary root gives rise to the main root of the plant and later becomes the tap root. Branches of the primary root are known as secondary roots or lateral roots.

coleoptile elongation and the plumule

In this stage, the coleopile elongates and emerges above the ground. A cluster of adventitious roots appear from the base of the radicle, and serve for anchorage and absorption. The plumule emerges through the coleoptile. It serves as a terminal bud which grows to form the shoot system.

By this time the primary root stops functioning and perishes sooner or later.

first true leaf start elongation from plumule

Only one cotyledon gives rise one leaf

developing first true leaf

Root system in young maize plant

The root system is completely replaced by adventitious roots. The cotyledon and endosperm remain buried in the soil, and decompose or fall off eventually. Numerous slender roots of adventitious type which are more or less equal in size and grow from the base of the stem. Such roots are called fibrous roots.

Developing and elongating maize plants

 The stem develops from the plumule of the embryo. A young stem with its leaves is called a shoot. Stems are normally slender and upright, but sometimes they become modified. The stem functions for supporting and conduction. The main trunk supports the whole plant and the branches bear leaves, flowers, fruits and emergences. To conduct water from the root to all the aerial parts and to conduct food manufactured by the leaves to the other parts of the plant.

In any leaf, the uppermost layer of cells and covered by a layer of cuticle without containing chloroplasts. Cuticle protects inner layers of leaf-cells. The upper epidermis reduces evaporation of water from leaf and allows light penetration to inner layers.
In an adult plant, the xylem cell carries water and minerals absorbed by roots to leaves. Phloem transports products of photosynthesis to other parts of the plants.
The veins branch repeatedly within the leaf so that every mesophyll cell is close to a xylem vessel which carries water to the leaf. The guard cells through controlling the opening of the stomata, regulate the transpiration stream and the water supply to the leaf.
Carbon dioxide, from the atmosphere, diffuses into the leaf through stomata. Carbon dioxide dissolves in the film of water around the cell wall before diffusing into the mesophyll cells.

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.