A plant embryo must have some strength before it pushes out of the soil.
It will first feed from the nutrients the seed has. Then it will start to grow up its roots downward in order to have the way to absorve energy from the soil. Once it is acquiring this energy from the soil, it will start growing the stem upward, opening up the space to push out of the soil.
After it has pushed out of the soil, the opening of the leaves and production of its own energy in the photosynthesis will take place.
