Mutations in AS1 affect the medial sepal-receptacle boundary. Scanning electron micrographs of wild-type and mutant sepal primordia. Boundary regions between the medial sepal (md se) primordia and underlying flower pedicels (pd) are indicated by arrowheads. A: In wild-type flowers (stage 8), a crease marks the site of the future sepal-receptacle (distal pedicel) boundary. B: This incipient boundary is shifted in as1 medial sepal primordia (stage 8). C: As wild-type flowers (stage 9) develop, the surface of the sepal is uniformly rounded. D: The central, proximal region of as1 sepal primordia (stage 9) protrudes from the surface. E: A well-defined boundary between the sepals and receptacle is present in wild-type flowers (stage 12). Trichomes are not observed in the proximal regions of sepals. F: The boundary between the medial sepals and pedicel is altered in as1 flowers (stage 12). Trichomes (see arrow, also in (C)) are frequently observed in the central, proximal regions of as1 medial sepals. Scale bars, 100 μm.