Germination

As germination is referred to in botany, both the first stage of ontogenesis in seeds and the sprouting of outlasting as rhizomes, tubers, bulbs or pollen and spores. Its special feature is the end of dormancy or dormancy; unwanted germination of cereal called outgrowth.

In a narrower sense, however, especially the beginning of the development of the seed of seed plants ( Spermatophyta ) is called germination. It includes the process of growth of the in- fertile seed embryos from the exit of the radicle to complete training of the seedling.

Conditions for germination

Water, heat, oxygen is needed for the germination of seeds, sometimes light or darkness. Different types of seeds need different germination conditions, especially the right temperature is important to overcome dormancy. Some seeds can only after frost or after forest fires to germinate ( stratification ). The seed is often very dry and needs to accommodate a large amount of water only, so his metabolism can start. For the first processes of growth, the nutrients in the seed, for example, oil or proteins are used as food. Hydrolases break down these nutrients and allow the embryo to move through growth of the shoot axis and the leaves to the light. Are these substances depleted and the light sufficient to gain the necessary energy from photosynthesis.

Types of germination

Depending on the type, a distinction between a epigeal or hypogean Keimungstyp.

Epigeal germination

In the epigeal (epi, gr: on / on; gae, gr: earth ) germination, the hypocotyl stretched. It forms a typical Hypokotylhaken, which breaks through the earth's surface and thus the seed leaves ( cotyledons ) uplifts. The cotyledons are up to the formation of the primary leaves ( = first episode leaves) photosynthetically active and die later from. Examples of the epigeal germination are radishes, beech, castor bean, potato and sunflower.

Hypogeous germination

In the hypogean ( hypo-, gr: under; gae, gr: earth ) germination, the epicotyl stretched so that the cotyledons remain in the soil. The first photosynthetic leaves are the primary leaves here. Examples of the hypogeous germination are pea, runner bean, oak and palm.

Evidence

• Gerhard Wagenitz: Dictionary of Botany. The terms in their historical context. 2nd expanded edition. Spektrum Akademischer Verlag, Heidelberg / Berlin 2003, ISBN 3-8274-1398-2, pp. 167-168.

• Plant development