Figure 2.

Positional references provided by the early embryo pattern.

Arrows indicate presumed pattern transmission mechanisms, which are discussed in sections 4 and 5.

(A) Triangular-stage embryo with central vascular cylinder (narrow cells in the center). Black arrows indicate signaling from the vascular cylinder to induce radial patterning in the overlying ground tissue (Section 5.3.); blue arrows indicate the likely dependence of hypophyseal cell fate acquisition on apical signals (Section 4.2.2.). Signals from hypophyseal derivatives (red arrows) confer stem cell identity in the root meristem (a.d. and b.d. = the apical and basal domains respectively. Section 4).

(B) Signals from the shoot meristem promote adaxial-abaxial polarity in leaves, while conversely, adaxial cell fate in leaf primordia promotes shoot meristem development, yellow arrows (Section 4.3.1).

(C) Positioning of lateral shoot organs. Primordia are restricted to the peripheral zone of the meristem. Initiated with an arbitrarily positioned cotyledon primordium (C1), graded lateral inhibition (indicated by green gradients) could restrict C2 to a position opposite C1 (Section 4.3.2). As subsequent leaf primordia (L1–L5) are produced, less synchronous differential inhibition would lead to a gradual transition of phyllotactic angles from 180° to 137°.