A seed is a plant in its infancy with a supply of nutrients.
With the help of seeds, plants multiply and spread. When the seed is in favorable conditions, it germinates.
The seed is placed in the soil. The soil is regularly moistened. First, the seed swells and then begins to germinate.
Aerial seed germination
Bean seed germination:
A – The seed coat cracks and a root appears that develops from the embryonic root.
B – The root grows and hardens in the soil.
C – Two cotyledons rise above the soil, which indicates the growth of the embryonic stem.
D – An aerial stem with leaves forms and turns green in sunlight.
In common beans, sunflowers, cabbage, cucumbers, onions, linden, the germinal stem carries the cotyledons into the air. This method of germination is called aboveground.
Underground seed germination
The cotyledons of seedlings of peas, barley, wheat, oak, hazel remain in the soil. They are characterized by an underground way of germination.
Wheat seed germinates underground.
At the narrow end of the grain, where the embryo is located, not one, but several roots develop, a fibrous root system is formed (1, 2).
A seedling is formed from the embryonic bud (3).
The formed seedling has a root system and an aerial shoot, consisting of a stem, leaves, and apical bud (4 – 6).
First, the embryo feeds on the nutrients stored in the seed itself.
When the seed runs out of nutrients, the new plant starts producing nutrients for itself. Photosynthesis is carried out in its leaves and green stem (organic matter is formed), and with the help of the roots, the plant absorbs water and minerals from the soil.
The main difference between underground germination (wheat grains) and aerial germination (bean seed) is that, with underground germination, one sprout first appears on the soil surface, and with aboveground germination, two cotyledons.
The germination capacity of plant seeds is different. So, the seeds of willow, poplar germinate immediately after getting on wet soil. If they do not form seedlings, then they die after 2 weeks. Seeds of other plants (lily of the valley, orchis, ginseng) are able to germinate only after a few years. Most plants retain the ability to germinate for a long time. Being in the soil, they form a kind of natural soil bank of seeds.