Fig. 1. Effects of phan and hb mutations on embryonic development. (A) Wild-type and phan mutant embryos form functional shoot apical meristems and dorsoventrally asymmetric cotyledons whereas phan hb double mutant seedlings produce ventralised cotyledons and either lack a functional SAM (left) or produce a SAM that terminates in formation of an ectopic leaf (right). (B) Scanning laser confocal micrographs of SAMs of wild-type seedlings (left) with a layered structure and recognisable central zone (CZ) which is lacking in phan hb double mutant seedlings (right).