Life begins from the seed for all plants alike. A seed is basically a shell that encloses in itself a small embryonic plant, covered by a hard seed coat, and some stored food, that upon receiving the appropriate climatic conditions, will promote growth.
The seed is the ripened or fertilized ovule (egg) of plants belonging to the superphylum Spermatophyta. This is the end product of the pollination process in which the female and male gamete fuse together to form a zygote, which grows and develops into the embryo, and the seed coat forms the outer protective shell.
The ability to consistently and successfully reproduce itself, via the use of seeds, engenders a higher survival rate in these plants as compared to those that rely on cuttings, runners, shoots, or rhizomes. Let us understand this amazing ability by reading through the germination process.
Process of Seed Germination
The seed contains an immature plant (embryo) that will give rise to an adult plant, complete with leaves and a root. The seed contains embryonic leaves called cotyledons; seeds that contain one embryonic leaf are known as monocotyledonous or monocots, whereas seeds with two embryonic leaves are termed as dicotyledonous or dicots.
The part from which the shoot develops is called the plumule, and the root develops from the radicle. It is the hypocotyl that transforms into the stem of the new plant. The food found in the seed, which nourishes the embryonic seedling during its early stages of development, is known as endosperm.
There are certain basics of seed germination. For a seed to germinate successfully the right conditions are required. Although, most seeds germinate under different conditions, it's the quality of the seed that matters, not its age. Lotus seeds as old as 2000 years have germinated, as the quality of their embryo was preserved.
Moisture or water is needed by the dried seeds to resume their cellular metabolism and growth. Moisture, combined with warmth, triggers growth, which is probably the reason why sown seeds should be kept in a warm place.
Warmth increases humidity, which ensures the presence of enough moisture for the seeds. The size of the seed and the depth it is sowed in determines how quick it will sprout through the soil. The larger the seed, more the energy stored in it, and vice-versa.
This is the reason why large seeds are sowed more deeper in comparison to smaller seeds. Whether a seed needs light (full or partial) or darkness to sprout depends upon its individual physiological need. The dormancy level of the seeds also determines the time it will take to germinate.
Dormancy is defined as the state of suspended growth. The period of dormancy varies with different plant species. In fact, dormancy is an adaptation that helps the plant to survive adverse growth conditions.
For example, certain seeds grow into new plants, only when they are exposed to some specific climatic condition, because if they germinate beforehand, the seedling may not survive.
When it comes to seed growth, there are different types of dormancy. In case of seed coat dormancy, the seed coat is too hard to imbibe water for the purpose of germination. Such seeds need to undergo weathering or action of microorganisms, so as to soften their outer coverings.
In case of embryo dormancy, the germination of the embryo is blocked till the seeds are exposed to favorable conditions. They need to be exposed to heat or cold, for a specific period, so as to germinate. Both seed coat dormancy and embryo dormancy are seen in some types of seeds.
There is another type of dormancy, wherein seeds contain certain chemicals that inhibit germination. If they are exposed to favorable conditions, the chemicals get removed, thereby facilitating germination.
For example, seeds of some desert plants do not germinate, till they are exposed to rain, as the water removes the chemicals in them. In short, dormancy is an important factor that affects seed germination.
Various techniques have been developed to overcome seed dormancy. For example, some types of seeds need to be chilled for a stipulated period, in order to induce germination. Another way to germinate seeds is by growing seeds without soil.
Germination of Seeds
Once the conditions for the process of seed germination have been satisfied, it is just a matter of time before they turn into seedlings. Some seeds, especially the ones with hard coats like the seeds of sunflower, morning glory, dates, acorn, corn, etc., need a couple of hours of pre-soaking to speed up the germination.
This activates enzymes that help in the replication of plant cells, and induce them to use the energy or food stored in the seed to give rise to the embryonic plant.
The seeds utilize this energy to produce the primary root, which penetrates the soil and starts functioning to absorb nutrients and water. This leads to the further development of the embryo, so as to give rise to the shoot of the plant.
When the shoot becomes too large, it bursts open through the seed coat, in search of light to start photosynthesis; and thus, the growing plant emerges. Both the root and shoot move downwards and upwards, respectively and simultaneously. In no time, the seedling forces its way through the soil.
The process of germination is amazing to watch, and also to understand the way it reproduces and ensures its species survival. So go ahead, sow a few seeds, and watch how life sprouts from the soil.