The part labelled I in A represents the "hypocotyl". The hypocotyl is the part of the embryonic stem of a plant that is located between the cotyledons (seed leaves) and the radicle (embryonic root). It is responsible for the elongation of the stem during germination and emergence of the seedling from the soil. The hypocotyl also helps to support the cotyledons and protects the developing shoot apical meristem.
