hypocotyl

/ˈhaɪpəˌkɑtəl/
noun
  1. The part of a plant embryo or seedling that is between the seed leaves (cotyledons) and the root. It is the stem-like region that pushes the cotyledons above the soil.
    • In the lab, we measured the length of the hypocotyl to see how the seedlings responded to light.
    • The gardener noticed that the hypocotyl of the young sunflower was thick and sturdy.
    • When a bean seed sprouts, the hypocotyl arches upward to pull the cotyledons out of the ground.