Figure 1. The isolated tobacco zygote and asymmetric two-celled proembryo in vivo and symmetric two-celled proembryo in vitro.

(A) An isolated zygote from ovule at 84 h after pollination; (B) An isolated asymmetric two-celled proembryo from ovule at 108 h after pollination; (C) A symmetric two-celled proembryo from in vitro culture for 1–1.5 d. Bar = 10 µm.