Seed parts and their functions

The seed consists of different parts, where each one is specialized in a function. These are the main parts of the seeds and their functions :

Embryo

The embryo is the new plant contained in the seed. It is very small and is in a state of lethargy. In turn, it is made up of:

• Radicle: constitutes the first rudimentary root in the embryo. Secondary roots and hairs form from the radicle that improve the absorption of nutrients.
• Plumule: it is the bud located on the opposite side to the radicle.
• Hypocotyl: this structure represents the space between the radicle and the plumule. Later with the germination of the seeds this part will become the stem of the plant.
• Cotyledon: this structure will form the first or the first two leaves of the plant. The number of cotyledons in a seed is a method of classifying a plant. Thus, they are divided into monocots and dicots. Learn more in this other post about What is a cotyledon .

Endosperm

The endosperm constitutes the food reserve of a seed, usually it is starch. It is also called albumen.

Episperm

The episperm is an outer layer and protects the seed from the environment. In gymnosperms it consists of a layer called the testa, while in angiosperms there are two, with a layer called the tegumen below the testa.

Cover

Also called integument, envelope or shell and it is a layer that surrounds and protects the central part of the seed and allows it to exchange water with the external environment.

Micropyle

It is a very important part of seed fertilization and allows water to enter the seed during germination.

The germination of the seed takes place when the conditions are the most suitable to ensure the survival of the future plant. Therefore the seed will remain in this dormant state until the germination process begins. For this process the most important thing is temperature and humidity , not being necessary light.

In germination, the radicle emerges first, which will enter the soil and continue to develop until giving rise to the roots . Its cotyledons will open and the hypocotyl underneath will begin to develop into the stem. Eventually, the cotyledons wither and new leaves will begin to sprout from the stem . In hypogeal germination, the cotyledons remain below the Earth, while in the epigea they remain above.

The classification of the seeds can be done according to several criteria:

According to its origin

By classifying the seeds according to their origin, we can divide them into:

• Angiosperm seeds: they come from angiosperm plants, that is, flowering plants that have seeds inside the fruits.
• Gymnosperm seed: originate from gymnosperm plants. These are seeds that are not found inside fruits, they can be in cones or cones.

According to the status of your reserve substances

Plant seeds have a number of reserve substances and differ in the places where they are stored:

• Endosperm seeds: in these seeds the reserve substances are found in the endosperm. These seeds are usually ideal for germination and are also widely consumed or used to make various products.
• Exendosperm seeds: the endosperm of this type of seed has been completely absorbed by the embryo and the reserve substances are stored in a structure of the embryo.
• Perisperm seeds: reserve substances are stored in a tissue called perisperm. These plants also have endosperm, but in a notably less amount so they receive the help of it.

According to the number of cotyledons

In this case the seeds can be monocotyledonous if they have only one cotyledon or dicotyledonous, if they have two. According to its conservation

In this case, they are classified as orthodox seeds, when they are of great durability and resistance to different conditions. On the contrary, recalcitrant seeds do not have great durability or resistance to conditions, so the ideal is to sow them after obtaining them.

According to its fruits

In this case they are classified according to the fruit to which they will give rise, although it is a very unspecific classification. Thus, we have seeds of grains, pseudo-cereals or legumes.

According to the different classification criteria, some of the examples of plants with seeds are:

• Grain seeds: for example oat or rice seeds.
• Pseudocereals seeds: An example is the amaranth seed.
• Legume seeds: lentil, alfalfa, or kidney bean seeds.
• Angiosperm seeds: apple, avocado or tomato seeds.
• Gymnosperm seeds: pine, fir or cypress seeds.
• Endosperm seeds: wheat, barley or corn seeds.
• Exoendosperm seeds: peanut or walnut seeds.
• Perispermed seeds: beet or pepper seeds.