Germination
What is germination?
Germination is the initial growth of a juvenile plant
Germination begins when seeds imbibe water and begin to swell,
This process ends with the emergence of true leaves and the plant photosynthesizing in order to obtain energy.
What structural changes occur?
Root establishment
Initially the true root, called the radicle, appears from the seed
After the radicle is established, the young shoot system emerges from the seed
Stem establishment
The embryonic shoot has two parts: the epicotyl and the hypocotyl
Epicotyl
The epicotyl is the true stem of the plant
It is the embryonic shoot above ("epi") the cotyledons
The tip of the epicotyl has a shoot apical meristem with true leaves (called the plumule)
Hypocotyl
A stem-like portion that acts as a transition between the radicle and the epicotyl
It is the embryonic shoot below ("hypo") the cotyledons
Some storage "roots" are examples of storage hypocotyls, including radish, celeriac, and rutabaga.
Above: Formation of a storage hypocotyl in radish (Raphanus sativa)
Leaf establishment
There are two types of embryonic leaves: the cotyledons and the true leaves
Cotyledons
Cotyledons are the embryonic food storage leaves of a seedling
Some plants store starches inside the cotyledons (e.g. beans, oak) for the developing seedling
Other plants store these starches inside the seed, but not the cotyledons (e.g. corn, radish)
Notice that some seedlings do not appear to have cotyledons, but they are present inside the seed underground (e.g. corn, oak)
Hypogeal germination: cotyledons remain in the seed underground
Other seedlings exhibit cotyledons above ground (e.g. radish, beans)
Epigeal germination: cotyledons appear above the soil level
