The structure in the maize grain that stores food is called the endosperm. It is a tissue that surrounds and nourishes the embryo of the seed. The endosperm is rich in starch, which serves as a source of energy for the growing embryo. During germination, the enzymes released by the embryo break down the starch in the endosperm to release the stored energy, which is then used by the developing plant to grow and establish itself. In other words, the endosperm is the part of the maize grain that provides the nourishment for the growing plant until it is capable of producing its own food through photosynthesis.