Fig. 1

Differential interference contrast (DIC) images of Arabidopsis thaliana ovules cleared by the standard procedure with prolonged incubation time in pure methyl salicylate up to 4 weeks. a Mature embryo sac with a central cell before polar nuclei fusion. b–f Subsequent stages of embryogenesis. b Globular-shaped embryo. c Late globular-shaped embryo. The bilateral symmetry of the proper embryo begins to form. d Late heart-shaped embryo. e Walking-stick-shaped embryo. f Mature embryo. ap, antipodal cells; co, cotyledon; ec, egg cell; gm, ground meristem; hc, hypocotyl; hy, hypophysis; pc, procambium; pd, protoderm; pn, polar nucleus in the central cell; r, radicle; su, suspensor; v, vacuole. Scale bars: 10 µm (a–c), 20 µm (d), 50 µm (e, f)