in epigeal germination the cotyledon is pushed above the ground,the hypcotyle is long and the epicotyle is short whereas in hypogeal germination the cotyledon stays below the soil, epicotyle is long and hypocotyle is short.
I'm not sure it's possible to give a reason, it's just evolution providing a slightly different solution to propogate the species, here's some reference material that might help:
epigeal
In botany, a seed is described as epigeal when the cotyledons of the germinating seed expand, throw off the seed shell and become photosynthetic above the ground.
The converse, where the cotyledons remain non-photosynthetic, inside the seed shell, and below ground, is hypogeal.
cotyledon
Cotyledons may be either epigeal, expanding on the germination of the seed, throwing off the seed shell and become photosynthetic above the ground; or hypogeal, not expanding, remaining below ground and not becoming photosynthetic. The latter is typically the case where the cotyledons act as a storage organ, as in many nuts and acorns.
There maybe some slightly different environmental factors that favor one approach over the other, but that's just a guess.
Here's some more: http://www.answers.com/topic/germination
I'm no expert but I think this might help:
From: http://www.answers.com/topic/epigeal In botany, a seed is described as epigeal when the cotyledons of the germinating seed expand, throw off the seed shell and become photosynthetic above the ground. The converse, where the cotyledons remain non-photosynthetic, inside the seed shell, and below ground, is hypogeal. And http://www.answers.com/topic/cotyledon Cotyledons may be either epigeal, expanding on the germination of the seed, throwing off the seed shell and become photosynthetic above the ground; or hypogeal, not expanding, remaining below ground and not becoming photosynthetic. The latter is typically the case where the cotyledons act as a storage organ, as in many nuts and acorns.
So as the seed of oil seed crops does not act as a storage organ, they are typically epigeal in nature.
Here's some more: http://www.answers.com/topic/germination
It helps the seeds breathe in and out through the stomata.
There are three types of germination 1.Hypogeal germination and epigeal germination and Cleistogeal germination. Hypogeal Germination: In this kind of Germination, the seed leaves or the cotyledons remain under the surface of soil. example: pea seeds - Epigeal Germination: In this type of Germination, the seed leaves grow above the ground on the new shoot. example: ash tree -Cleistogeal Germination: A special leaf that has a central umbrella like stalk forms above the ground which protects the shoot from any damage. So the development of the shoot can not be seen.
the cotyledons come up above the soil surface
Generally seed require a few things in order to germinate:Water/ moistureSoil (or a growing medium)Heat/ warmthDarkness or in the case of some seed lightGeneral guide is that the seed should be covered to double the diameter of the seed itself. In the case of many small or fine seed varieties it is best to leave them uncovered with soil.Keep the soil moist during germination, but not too wet as this can cause fungal problems.It is always best to research the seed variety you are germinating if you are not sure of the specifics - as different seeds have different germination periods.
Surface Geologic Processes also reffered to as, Exogeneous Geologic Processes, are the processes that operates on the Earth's surface and helps to reconstruct the Earth externally. They include, Erosion, Weathering, Mass Wasting, Orogeny. Their agents are called the Epigeal Geological Agents, and include, Wind, Water, Glacier, Waves etc.
in epigeal germination cotyledons and plumule comes out from soil in hypogeal germinatin only plumule comes out from soil
examples of hypogeal germination is mango and epigeal is bean
Epigeal germination is when the cotyledons emerge above the soil surface during seed germination. Hypogeal germination is when the cotyledons remain below the soil surface during seed germination.
Do sunflower undertake epigeal germination
no it is epigeal type of germination because the cotyledons are under the soil
hypogeal
Epigeal germination is the process in which the seed leaves or the cotyledons are brought on to the surface along with the shoot during germination. Hypogeal germination is the process in which the seed leaves or the cotyledons remain below the soil surface during germination.
It helps the seeds breathe in and out through the stomata.
There are three types of germination 1.Hypogeal germination and epigeal germination and Cleistogeal germination. Hypogeal Germination: In this kind of Germination, the seed leaves or the cotyledons remain under the surface of soil. example: pea seeds - Epigeal Germination: In this type of Germination, the seed leaves grow above the ground on the new shoot. example: ash tree -Cleistogeal Germination: A special leaf that has a central umbrella like stalk forms above the ground which protects the shoot from any damage. So the development of the shoot can not be seen.
I'm no expert, but I believe yes: From: http://www.answers.com/topic/epigeal In botany, a seed is described as epigeal when the cotyledons of the germinating seed expand, throw off the seed shell and become photosynthetic above the ground. The converse, where the cotyledons remain non-photosynthetic, inside the seed shell, and below ground, is hypogeal. And http://www.answers.com/topic/cotyledon Cotyledons may be either epigeal, expanding on the germination of the seed, throwing off the seed shell and become photosynthetic above the ground; or hypogeal, not expanding, remaining below ground and not becoming photosynthetic. The latter is typically the case where the cotyledons act as a storage organ, as in many nuts and acorns. And http://www.answers.com/topic/germination
name few seeds that undergo epigeal growth
Eggplant type of germination is epigeal since it's cotyledon turn green and undergo phtosynthesis.