Types of Germination
(a) Epigeal germination e.g. bean
Cotyledons are brought above the ground during germination due to elongation of hypocotyls e.g. bean
During germination of a bean seed, the radicle grows out through the micropyle.
It grows downwards into the soil as a primary root from which other roots arise.
The part of the embryo between the cotyledon and the radicle is called the hypocotyl.
This part curves and pushes upwards through the soil protecting the delicate shoot tip.
The hypocotyl then straightens and elongates carrying with it the two cotyledons, which turn green and leafy.
They start manufacturing food for the growing seedling.
The plumule, which is lying between two cotyledons, begins to grow into first foliage leaves, which start manufacturing food.
(b) Hypogeal germination e.g. maize
The cotyledons remain below the surface during germination due to elongation of epicotyl e.g. maize
In maize, the endosperm provides food to the embryo that begins to grow.
The radicle along with a protective covering (coleorhiza) grows out of the seed.
The epicotyl is the part of the embryo between the cotyledon and the plumule.
The epicotyl elongates and the plumule grows out of the coleoptile and forms the first foliage leaves.
The seedling now begins to produce its own food and the endosperm soon shrivels.