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Why do bean and sunflower cotyledons emerge above the ground?

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Cluster of bright red seeds emerging from the cone-shaped fruit of a magnolia grandiflora, surrounded by large, glossy green leaves. — Seed Fruit and seeds of the southern magnolia (*Magnolia grandiflora*). The fruit is an aggregate of follicles, and each follicle bears a single red seed.

Bean and sunflower plants exhibit a pattern of development known as epigeal germination. In this process, the hypocotyl—the embryonic stem located between the radicle and the cotyledons—elongates and grows several inches above the soil surface.123

This elongation of the hypocotyl is what physically pushes the cotyledons, the epicotyl, and the remains of the seed coat out of the ground and into the light. Once exposed, the cotyledons may expand and become green, functioning photosynthetically as leaves, or they may simply transfer their stored nutritional reserves to the developing seedling before degenerating. This strategy contrasts with hypogeal germination, where the hypocotyl remains short and the cotyledons stay underground.123