Maize seed. Light micrograph of a section through the seed of a maize plant (Zea mays), showing the embryo. The embryonic area includes a radicle (bottom right) and plumule (not seen). These are the structures by which the seed will germinate and develop a root and leaf system respectively, developing into a new plant. Maize is a crop that is cultivated for its grains, which are a rich source of starch.