Shoot apex organization during the embryogenesis and early seedling phases of development. (A) Median longitudinal section of the shoot apex in a zygotic embryo 80 d after pollination (DAP). Inset: a complete longitudinal section of the corresponding zygotic embryo. (B) Median longitudinal section of the shoot apex in a zygotic embryo 120 DAP. Inset: a complete longitudinal section of the corresponding zygotic embryo. (C) Median longitudinal section of a 1-week-old seedling. Note the well-differentiated shoot and root apices. (D) Higher magnification view of (C) in the shoot meristematic dome. The type of organ originating from each primordia is indicated in parentheses in (A), (B) and (D). Abbreviations: *, meristematic dome; arm, axillary root meristem; cs, cotyledonary slit; hau: haustorium (i.e. cotyledon); l1–l2, leaf; P1–P2–P3, primordia; pcs, procambium strand; prm, primary root meristem; sl1–sl2, scale leaf. Scale bars: (C, inset in A, inset in B) = 250 µm; (A, B, D) = 100 µm.