The germination process begins when water is absorbed (imbibed) by the seed. This initiates several biochemical events necessary for seedling development. For example, enzymes secreted from the aleurone layer, break down starch in the endosperm converting it to simple sugars which nourish the embryo. All structural components of the grass seedling arise from the embryo. The endosperm provides a quick source of energy for the developmental process, whereas the cotyledon (rich in fats and oils) provides energy for later stages of development.