Germination occurs when all the proper variables are in place for that particular variety (oxygen, temperature, light or darkness) and the seed coat absorbs water, causing it to swell and rupture.
The first sign of life comes from the radicle, a little white tail that eventually becomes the primary root of the plant.
The role of the radicle is to anchor the plant in the ground and start absorbing water.
Once it absorbs water, a rudimentary stem emerges and the cotyledons start to unfurl, often taking the seed coat with them as they rise above the soil.
Sometimes they’re called seed leaves, because they’re part of the seed or embryo of the plant. Their function is to absorb all the endosperm and become the temporary stores of the plant’s initial supply of nutrients.