The germination is the resumption of the development and the Métabolisme (absorption of water (imbibition), breathing, enzymatic activity, etc) of a Embryon of Spermatophyte, until it becomes an adult plant.
It is considered that germination starts when the seed is put in contact with water, (if the external conditions are favorable) and finishes when the radicle bored the cuticule.
It occurs only if the external conditions (moisture, temperature, oxygen.) are favorable; just as the internal factors (maturity, viability, dormancy, effect of the light.). Certain seeds can germinate only after having undergone an intense cold which raises the Dormance S, it is the Vernalisation (so called " stratification").
The " to be able germinatif" vary according to the species, of a few days to several centuries.
At the end of germination, the cotyledons, having fulfilled their role, fade and leave the place to the true sheets which take their relay to feed the plant thanks to the Photosynthèse.
Types of germination
- épigée germination : As at the Bean for example. The seed is raised out of the ground by fast increase in tigelle which gives the axis Hypocotyle which raises both Cotylédon S out of the ground. The Gemmule develops (after the Radicule) and gives a stem broken into leaf above the two cotyledons. The first internode gives the épicotyle. The first sheets, above the cotyledons are the paramount sheets (they are simpler than the future sheets).
hypogean germination : As at the Corn. The seed remains in the ground, the tigelle one does not develop and the cotyledons remain in the ground.
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